Dissertations / Theses on the topic 'Crops irrigation'

Thesis (MScAgric)--University of Stellenbosch, 2003.
ENGLISH ABSTRACT: Poor water management and poor water use efficiency (WUE) have been identified as one of the major problems experienced by vegetable growers in most of the developing countries, including South Africa. This poor management and poor utilization of water have led to a drastic decline in the quality and quantity of available water. In South Africa agriculture uses about 50% of available water. Increasing water demand for domestic, industrial and mining uses, may decrease agriculture's share to less than the current 50%, henceforth, better utilization of this resource is imperative. Selection of a good irrigation system can limit water loss considerably. Some irrigation systems have a potential to save more water than others do. Since irrigation systems affect the WUE of crops, care should be taken when selecting an irrigation system under conditions of limited water quantity. Ebb-and- Flood watering systems have been introduced for effective sub-irrigation and nutrient delivery within closed systems. Such a system was adapted in South Africa, to develop a vegetable production unit for use by families in rural communities, while saving substantial amounts of water. A need to further improve the WUE of this system was subsequently identified. Two studies were conducted at the experimental farm of the University of Stellenbosch (Department of Agronomy). The first trial was conducted under controlled conditions in a glasshouse, and the second under open field conditions. In the first trial, Beta vulgaris (Swiss chard) and Amaranthus spp. ('Imbuya') were grown in two root media; gravel and pumice. In addition, an 'Ebb-and-Flood' and a 'Constant level' system were used with nutrient solutions at two electrical (EC) conductivity levels 1.80 and 3.60 mS cm-I. The results of this (2x2x2x2) factorial experiment indicated that a combination of the 'Ebb-and-Flood' system with gravel as a root medium produced the best results at a low EC, when 'imbuya' was used. A high total WUE was found with 'imbuya', (7.35 g L-I) at EC 1.80 mS cmicompared to a relatively low WUE of 5. 90 g L-I when the 3.60 mS cm-I nutrient solution was used. In the second trial, 'Imbuya's' foliage dry mass, leaf area and WUE was evaluated under field conditions at the Stellenbosch University experimental farm, during the summer of2002. The experimental farm (33°55'S, 18°52'E) is situated in the cooler coastal wine grape-producing region of South Africa with a relatively high annual winter rainfall. This trial was conducted on an alluvial soil, with clay content of 25% and a pH of 5.9 (KC!). A closed 'Ebb-and-Flood' system was compared with two open field irrigation systems ('Drip' and 'Flood') using nutrient solutions at two electrical conductivity levels (1.80 and 3.60 mS cm-i) in all three cases. Foliage dry mass, leaf area as well as WUE was best with 'Drip' irrigation, when a nutrient solution with an electrical conductivity of 3.60 mS cm-i was used. In spite of the fact that additional ground water was available for the soil grown 'Drip' and 'Flood' treatments, the 'Ebb-and-Flood' system outperformed the 'Flood' treatment, especially when the nutrient solution with an EC of 3.6 mS cm-i was used. Insufficient root aeration in the flooded soil could have been a contributing factor. The fact that the 'Ebb-and-Flood' and 'Drip' systems gave the best results when the high EC solution was used to fertigate the plants, may indicate that the plants could have hardened due to the mild EC stress, better preparing them to adapt to the extreme heat that was experienced in the field.
AFRIKAANSE OPSOMMING: Swak: bestuur van water en 'n swak: water-gebruik-doeltreffendheid (WOD) is as een van die belangrikste probleme geïdentifiseer wat deur groente produsente in die meeste ontwikkelende lande, insluitend Suid-Afrika, ervaar word. Hierdie swak bestuur en benutting van water het daartoe bygedra dat 'n drastiese afname in die kwaliteit asook in die kwantiteit van beskikbare water ervaar word. In Suid-Afrika gebruik die landbou-sektor ongeveer 50% van die beskikbare water. Toenemende water behoeftes vir huisgebruik, industrieë en die mynbou mag hierdie 50% aandeel van die landbou sektor laat krimp. Beter benutting van hierdie skaars hulpbron is dus noodsaaklik. Die keuse van goeie besproeiingsisteme mag waterverliese merkbaar beperk aangesien sekere sisteme se water-besparingspotensiaal beter as ander is. Aangesien besproeiingstelsels die WOD van gewasse beïnvloed, is spesiale sorg nodig waar 'n besproeiingstelsel onder hierdie toestande van beperkte waterbronne gekies moet word. 'Ebb-en-Vloed' sisteme kan aangewend word om water en voedingselemente van onder in 'n wortelmedium te laat opstoot en in 'n geslote sisteem te laat terugdreineer. So 'n sisteem is in Suid-Afrika ontwikkel waarmee groente vir families in landelike gebiede geproduseer kan word terwyl water bespaar word. 'n Behoefte om die WOD van hierdie produksiesisteem verder te verbeter is egter geïdentifiseer. Twee ondersoeke is by die Universiteit van Stellenbosch se proefplaas (Departement Agronomie) gedoen. Die eerste proef is onder beheerde omgewingstoestande in 'n glashuis uitgevoer en die tweede onder veld toestande. In die eerste proef is Beta vulgaris (Snybeet) en Amaranthus spp. ('Imbuya') in twee tipes wortelmedia; gruis en puimsteen verbou. 'n 'Ebb-en-Vloed' asoook 'n 'Konstante vlak' besproeiingsisteem is gebruik terwyl voedingsoplossings ook by twee peile van elektriese geleiding (EC) teen 1.80 en 3.60 mS cm-I toegedien is. Die resultate van hierdie (2x2x2x2) fakroriaal eksperiment het aangetoon dat 'n kombinasie van die 'Ebb-en-Vloed' sisteem met gruis as 'n wortelmedium die beste resultate teen 'n lae EC lewer waar 'imbuya' gebruik is. Die WOD met 'imbuya' was hoog (7.35 g L-1) by 'n EC van 1.80 mS cm-I, vergeleke met 'n relatief lae WOD van 5. 90 g L-1 waar die 3.60 mS cm-I voedingsoplossing gebruik is. In die tweede proef is 'Imbuya' se droë blaarmassa, blaar oppervlakte en WOD onder veldtoestande op die Universiteit van Stellenbsoch se proefplaas in die somer van 2002 ge-evalueer. Die proefplaas (33°55'S, 18°52'E) is in die koeler kusstreke van die wyndruif produksiegebied in die winterreëngebied van Suid-Afrika geleë. Hierdie proef is op alluviale grond met 25% klei en 'n pH van 5.9 (KCi) uitgevoer. 'n Geslote 'Ebb-en-Vloed' sisteem is met twee veld-besproeiingsisteme vergelyk ('Drup' en 'Vloed') terwyl voedingsoplossings teen twee peile van elektriese geleiding (1.80 en 3.60 mS cm-I) in al drie gevalle gebruik is. Blaar droëmassa, blaaroppervlakte asook die WGD was die beste met 'Drup' besproeiing waar die EC van die voedingsoplossing 3.60 mS cm-I was. Ten spyte van die feit dat ekstra grondwater vir die 'Drup' and 'Vloed' behandelings beskikbaar was, het die 'Ebben- Vloed' stelsel beter as die 'Vloed' behandeling gedoen veral waar die voedingsoplossing se EC 3.6 mS cm-I was. Swak wortelbelugting was waarskynlik die rede waarom vloedbesproeiing swak produksie gelewer het. Die feit dat die 'Drup' en die 'Ebb-en-Vloed' behandelings in die veldproef die beste gedoen het waar die EC hoog was, mag moontlik met die gehardheid van die plante verband hou wat aan ekstreem warm en dor toestande blootgestel was.

Effect of Alkalinity in Irrigation Water on Selected Greenhouse Crops. (August 2004) Luis Alonso Valdez Aguilar, B.S., Universidad Aut??noma de Nuevo Le??n, Mexico; M.S., Universidad Aut??noma Chapingo, Mexico Chair of Advisory Committee: Dr. David Wm. Reed Bicarbonate (HCO3-) and carbonate (CO32-) are the most important ions that determine alkalinity. When the carbonates accumulate in a growing medium, the growing medium solution pH reaches levels that cause plant growth inhibition, which is caused primarily by the transformation of soluble forms of Fe into insoluble forms. The general objective of this research was to provide information about the limits of tolerance to alkalinity in ornamental plants, and to study the interaction of ions such as ammonium (NH4+) and nitrate (NO3-) on the response of plants to alkalinity, as well as the effect of the counter-ions potassium (K+), sodium (Na+), cesium (Cs+), ammonium (NH4+) and rubidium (Rb+). The maximum SPAD index was estimated to occur at 0 mM of NaHCO3 in chrysanthemum, mini-rose, and hibiscus ??Bimini Breeze?? and ??Mango Breeze??. For vinca it was set at 2.64 mM. A 15% decrease from the maximum SPAD index was considered the threshold to declare the toxic concentration of NaHCO3, which was calculated based on the maximum SPAD index predicted by the models. The toxic concentration of NaHCO3 was set at 4.1, 1.1, 6.7, 3.1, and 6.3 mM of NaHCO3 in chrysanthemum, mini-rose, vinca, and hibiscus ??Mango Breeze?? and ??Bimini Breeze??, respectively. Hibiscus ??Bimini Breeze?? was considered tolerant to alkalinity, due to increased Fe-reduction capacity and acidification of the growing medium. In the hydroponic experiment, results showed that the NH4+:NO3- ratio altered the response of sunflower plants to alkalinity. Sunflower plants grew better in solutions containing 5 mM NaHCO3 prepared with a 0.25:0.75 NH4+:NO3- ratio. This was possible due to the reaction of NH4+ with the HCO3-, which reduced its buffering capacity. The response to HCO3--induced alkalinity was modified by the counter-cation of HCO3-. In bean plants, at low-to-intermediate levels of Na+ and HCO3- induced approximately same growth decrease. At high concentration, Na+ induced a decrease on shoot growth that exceeded the toxic effects of HCO3-. Thus, the toxic effect of Na+ is higher than that of HCO3- when its concentration is high. Rubidium was extremely toxic at concentrations of 7.5 mM.

As global water resources decline, reuse of domestic greywater for the irrigation of home gardens is quickly becoming widespread in many parts of the world. However, the sanitary implications of reusing greywater to water edible crops remain uncertain. This study examined the benefits and risks associated with domestic greywater reuse for the purposes of vegetable garden irrigation. Untreated (settled only) and treated (settling and slow sand filtration) greywater collected from a family home was analyzed for basic water quality parameters, over a period of eight weeks. During that time, both greywaters were used to irrigate individually potted plots of lettuce, carrots and peppers in a greenhouse. Tap water was used as control. Upon maturity, plants were harvested and the edible portions tested for fecal coliforms and fecal streptococci, common indicators for the presence of pathogenic microorganisms. Heavy metals were not detected in the greywater, but both fecal coliforms and fecal streptococci were present in high levels, averaging 4 x 105/100mL and 2 x 103/100mL of greywater, respectively. Despite these high counts, no significant difference in contamination levels was observed between crops irrigated with tap water, untreated and treated greywaters. Fecal coliform levels were highest in carrots and fecal streptococcus levels highest on lettuce leaves. However, contamination levels for all crops were low and do not represent a significant health risk. Plant growth and productivity were unaffected by the water quality, owing to the low N, P and K levels of the greywater. These results reinforce the potential of domestic greywater as an alternative irrigation source
Dans le contexte d'un déclin et d'une perte de fiabilité des ressources hydriques du globe, la réutilisation des eaux grises (eaux le lavage) domestiques pour les fins d'irrigation devient une option populaire pour les ménages un peu partout dans le monde. Pourtant, les implications sanitaires d'une telle pratique pour l'irrigation des plantes comestibles ne sont pas encore bien comprises. Cette étude vise à examiner les bénéfices et risques associés à la réutilisation des eaux grises pour arroser les jardins potagers domestiques. Il met son focus sur la possibilité de contamination des légumes par des organismes pathogéniques et les métaux lourdes qui peuvent être présents dans les refuts domestiques. Les eaux grises d'une famille montréalaise ont été collectionnés et analysés pour des paramètres de base, y inclut les pathogènes et les métaux lourds, sur une période de 8 semaines. Pendant ce temps, ces eaux grises ont été utilisés à irriguer des plantations individuels de laitues, carottes, et poivrons rouges dans une serre de recherche. L'eau du robinet a servi comme contrôle. À la maturité, les plantes ont étés cueillis et les portions comestibles testés pour la présence des coliformes et des streptocoques fécaux, deux bactéries normalement utilisés pour indiquer la présence d'organismes pathogéniques. Puisque les métaux lourds n'étaient pas présents dans les eaux grises, ils n'ont pas étés testés dans les légumes. Les résultats ont indiqué un niveau élevé de bactéries indicateurs dans les eaux grises, mais la différence de contamination entre les légumes irrigués avec les eaux de robinet et ceux irrigués ave

Research on greywater irrigation has mainly focused attention on the reuse of greywater in relation to its quality and crop biomass but not on quality of edible vegetable crops. Thus a field experiment was established at the Umtata Dam Research Station where combinations of cabbages and onions; spinaches and beetroots; and carrots and lettuce were planted in to coincide with four different planting seasons (from October 2009 to December 2010). Crops were irrigated with greywater generated from bathing and dishwashing. Greywater was collected from a number of households in the vicinity of the Umtata Dam, in the Eastern Cape Province of South Africa. In the field experiment, vegetables were planted in three plots of the same composition of soil properties and then drip irrigated separately either with greywater, potable water, or with diluted greywater at a ratio of 1:1. The greywater quality, yield, aesthetical appeal, plant chemical analysis and soil chemical analysis were measured. Irrigation from diluted greywater showed a significant increase in yield, in the head mass and in appeal of cabbages. Onion yields were significantly higher when irrigated with greywater. Spinach also obtained significantly higher yields when irrigated with greywater, however many leaves from this treatment were infested with leaf-spot disease. Beetroot yield and quality was not affected with greywater irrigation, instead yield was reduced by 47% (4.686 tons/ha). Carrots did not show any significant difference in yield and root girth, but carrots irrigated with potable water were more appealing and longer in length. Lettuce irrigated with dilute greywater was significantly more appealing than other treatments. Sodium (Na) ions were elevated in cabbage, onions and were significantly higher in the case of lettuce and carrots when irrigated with greywater. Crude protein (CP) was observed to be significantly elevated on cabbages and lettuce when irrigated with diluted greywater whereas CP of onions and carrots were significantly lower due greywater irrigation. Significant increases in iron (Fe) were observed on cabbages and spinach when irrigated with diluted greywater, whereas lettuce Fe content was significantly elevated by greywater irrigation. There was no significant difference in cadmium (Cd) caused by irrigating spinach and lettuce with greywater, also those heavy metals that were significantly higher, were within the accepted threshold leaving the conclusion that lower levels of heavy metals posed no health risks to humans. In conclusion, greywater used in this study does not appear to cause an accumulation of salts and heavy metals in plants and soil, which suggests in this instance, that greywater does not pose a threat to plants and soils.

Albeit much effort having been put to review the performance trend of smallholder irrigation farmers in South Africa. However, there seems to be a paucity of information regarding the level of entrepreneurship on these farmers. Most research works on smallholder irrigation farmers have mainly focused on livelihoods trajectory providing a review on how the welfare of the rural poor has been transformed after the introduction of irrigation schemes. With most research evidence indicating a high degree of underperformance on most smallholder irrigation schemes, this research attempted to investigate the level of entrepreneurship among the small holder irrigation farmers. In order to achieve the main research objective, a sample of 110 farmers drawn from Qamata irrigation scheme was interviewed and each farmer’s performance on the nine components of entrepreneurship was assessed. The aspects assessed to determine the farmer’s entrepreneurial behaviour were: planning ability, risk taking, achievement motivation, leadership ability, Cosmo politeness, decision making, and innovativeness and farming knowledge. Basing on previous studies which indicated entrepreneurial behaviour to be influenced by several factors the study also analysed the determinants of entrepreneurship among the irrigation farmers and a binary logistic regression model was used to establish the connection between various independent variables and the farmers’ entrepreneurial performance given as a total score of the nine components. Though the findings of the study revealed a prevalently low level of entrepreneurship among the smallholder irrigation farmers on Qamata irrigation scheme, a high proportion of the respondent farmers (65.5% and 60.5%) showed to have a high degree of achievement motivation and decision making ability, respectively. The observed trend thus reflected that smallholder farmers have a potential to become entrepreneurs and are willing to succeed. The binary model results revealed that the prevailing land tenure system will be a strong determinant of the farmer’s level of entrepreneurship. Equally, levels of training in farming, motive for farming and information seeking tendency also proved to have a significant influence on the degree of farmer entrepreneurship. Based on the results of this study recommendations have thus been drawn on the need for policies and practices aimed at promoting entrepreneurship and not dependency among farmers. Key focus areas identified include: the need to revise the current land ii tenure system on irrigation schemes, intensify on entrepreneurship training for both farmers and extension officers and regular on-farm training on new technologies.

Water use is an important topic in the global agriculture community and is a critical input in nursery crop production. Several plants in the genus Cornus are important nursery crops. Not only are they economically relevant, they are found in grafted and seedling forms and parents and their hybrid are readily available in the trade, facilitating an assessment of water requirements. Anecdotal information suggests that Cornus taxa have differing stress tolerance and water use requirements. Research was conducted to characterize and model water use among Cornus taxa. Scanning electron microscopy and anatomy‐based micromorphological studies as well as transpiration chamber‐based studies revealed differences in the cuticle, epidermal thickness, stomatal density, total stomatal complex area, and gas exchange. A novel photosynthesis‐based irrigation model was developed and evaluated, first on a model crop, Hibiscus rosa‐sinensis, then with a range of Cornus taxa, including grafted specimens. The model allowed the identification of a setpoint or point at which irrigation is triggered. Producing plants under this model allowed a 27% reduction in water use while maintain growth when compared with controls.

The study examined the impact of small scale irrigation technology in crop production under Ncora areas of Cofimvaba. To achieve the objective of the study, data were collected from 212 farmers engaged in various crop enterprises under the Ncora. The farmers were randomly selected. Descriptive Statistics, DEA model, linear regression model and gross margin analysis were used to analyse the results obtained from the survey. The descriptive results showed that Ncora farmers are small-scale farmers cultivating small hectare of land and using simple farm tools, mainly using furrow irrigation. Furthermore, they produce more than one crop enterprises. The gross margin Analysis shows that Ncora cultivation is profitable. The most profitable crop was found to be maize than potatoes. Farm production function revealed that land, labour and purchased inputs had a positive relationship with the output of the enterprises. SPSS was used to run data for linear regression model (OLS). It was suggested that extension services and private organizations assist farmers especially the emerging ones via provision of training, processing and storage facilities. Furthermore, continuous monitoring of soil and water quality as well as ground water table was recommended, in order to ensure sustainability of Ncora irrigation in the area.

Increased water- and fertilizer-use-efficiency in containerized crop production, via reduced water loss, enhances crop-available nutrients while reducing non-point source agrichemical contributions in accordance with regulatory standards. Previous studies detailed nutrient leaching patterns throughout crop production seasons, leaving little known about water and dissolved nutrient (solute) movement through soilless substrates during irrigation. The following experiments evaluated fundamental water and solute transport principles through pine-bark based substrates. 1) Ilex crenata Thunb. 'Bennett's Compactum' were grown in 2.7 L containers. Tensiometers detected wetting front (WF) movement throughout the substrate during irrigation. 2) Tracer solution (containing NO3-, PO43- and K+) and deionized water (DI) were applied to substrate-filled columns to characterize tracer breakthrough under saturated and unsaturated conditions. 3) Controlled-release fertilizer (CRF) was topdressed (surface-applied), incorporated (throughout substrate), dibbled (center of substrate) or not applied to fallow substrate, irrigated with DI and leachate analyzed to determine nutrient concentrations throughout irrigation. Tensiometers revealed that seasonal root growth affected substrate pre-irrigation moisture distribution. Wetting fronts channeled through the substrate before becoming thoroughly wetted. Tracer breakthrough occurred with less effluent volume under unsaturated conditions. Breakthrough of NO3- and PO43- was relatively conservative, though 37% of K+ was retained by the substrate. Leachate concentrations for topdressed and incorporated CRF peaked early (first 50mL effluent) before diminishing with continued leaching. Leachate concentrations for dibbled CRF initially increased (first 150mL leachate), plateaued and then diminished. These results show the relative rapidity which water and solutes move through pine-bark during irrigation and demonstrate methods for future research on within-irrigation solute transport.
Master of Science

Les terres cultivées représentent un cinquième de la surface émergée de la Terre. Elles fournissent des nutriments à l'homme, modifient le cycle biogéochimique et l'équilibre énergétique de la terre. L’évolution des terres cultivées dans le contexte du changement climatique et avec une intensification des actions anthropiques constitue un enjeu important pour la sécurité alimentaire et les exigences environnementales du développement durable. Le manuscrit de thèse s’inscrit dans cette thématique en exploitant les données de différentes sources et la modélisation numérique. Les données utilisées sont : les statistiques de rendements, les observations agro-météorologiques à long terme, les résultats des sites d’expérimentation avec du réchauffement, les jeux de données globales issus des processus de fusion ou d’assimilation, les données climatiques historiques et de projection future. La modélisation fait appel aux modèles statistiques et aux modèles de processus. Le manuscrit est composé d’une série de travaux de détection et d'attribution. Ils explorent la phénologie, le rendement et leurs réponses aux changements climatiques et aux pratiques de gestion. Ils sont soit sur l'échelle régionale soit sur l’échelle globale, en fonction de la disponibilité des données et de leur pertinence. Le chapitre 2 décrit la construction et l’utilisation d'un modèle statistique avec des données provinciales de rendement au Nord-est de Chine et des données climatiques historiques. Les résultats montrent un effet asymétrique de la température diurne sur le rendement du maïs. Le rendement du maïs augmente de 10.0±7.7% en réponse à une augmentation moyenne de 1oC pendant la saison de croissance quand il s’agit de la température minimale de nuit (Tmin), mais le rendement diminue de 13,4±7,1% quand il s’agit de la température maximale de jour (Tmax). Il y a une grande disparité spatiale pour la réponse à Tmax, ce qui peut s'expliquer partiellement par le fort gradient spatial de la température pendant la saison de croissance (R = -0,67, P <0,01). La réponse du rendement aux précipitations dépend aussi des conditions d'humidité. Malgré la détection d'impacts significatifs du changement climatique sur le rendement, une part importante de ses variations n’est pas expliquée par les variables climatiques, ce qui souligne le besoin urgent de pouvoir attribuer proprement les variations de rendement au changement climatique et aux pratiques de gestion. Le chapitre 3 présente le développement d’un algorithme d'optimisation basé sur la théorie de Bayes pour optimiser les paramètres importants contrôlant la phénologie dans le modèle ORCHIDEE-crop. L’utilisation du modèle optimisé permet de distinguer les effets de la gestion de ceux du changement climatique sur la période de croissance du riz (LGP). Les résultats du modèle optimisé ORCHIDEE-crop suggèrent que le changement climatique affecte la LGP différemment en fonction des types du riz. Le facteur climatique a fait raccourcir la LGP du riz précoce (-2,0±5,0 jour / décennie), allonger la LGP du riz tardif (1,1±5,4 jour / décennie). Il a peu d'effet sur la LGP du riz unique (-0,4±5,4 jour / décennie). Les résultats du modèle ORCHIDEE-crop montrent aussi que les changements intervenus dans la date de transplantation ont provoqué un changement généralisé de la LGP, mais seulement pour les sites de riz précoce. Ceci compense à la hauteur de 65% le raccourcissement de la LGP provoquée par le changement climatique. Le facteur dominant du changement LGP varie suivant les trois types de riz. La gestion est le principal facteur pour les riz précoce et unique. Ce chapitre démontre aussi qu'un modèle optimisé peut avoir une excellente capacité à représenter des variations régionales complexes de LGP
Croplands accounts for one-fifth of global land surface, providing calories for human beings and altering the global biogeochemical cycle and land surface energy balance. The response of croplands to climate change and intensifying human managements is of critical importance to food security and sustainability of the environment. The present manuscript of thesis utilizes various types of data sources (yield statistics, long-term agrometeorological observations, field warming experiments, data-driven global datasets, gridded historical climate dataset and projected climate change) and also modelling approaches (statistical model vs. process model). It presents a series of detection and attribution studies exploring how crop phenology and crop yield respond to climate change and some management practices at regional and global scales, according to data availability. In Chapter 2, a statistical model is constructed with prefecture-level yield statistics and historical climate observations over Northeast China. There are asymmetrical impacts of daytime and nighttime temperatures on maize yield. Maize yield increased by 10.0±7.7% in response to a 1 oC increase of daily minimum temperature (Tmin) averaged in the growing season, but decreased by 13.4±7.1% in response to a 1 oC warming of daily maximum temperature (Tmax). There is a large spatial variation in the yield response to Tmax, which can be partly explained by the spatial gradient of growing season mean temperature (R=-0.67, P<0.01). The response of yield to precipitation is also dependent on moisture conditions. In spite of detection of significant impacts of climate change on yield variations, a large portion of the variations is not explained by climatic variables, highlighting the urgent research need to clearly attribute crop yield variations to change in climate and management practices. Chapter 3 presents the development of a Bayes-based optimization algorithm that is used to optimize key parameters controlling phenological development in ORCHIDEE-crop model for discriminating effects of managements from those of climate change on rice growth duration (LGP). The results from the optimized ORCHIDEE-crop model suggest that climate change has an effect on LGP trends, but with dependency on rice types. Climate trends have shortened LGP of early rice (-2.0±5.0 day/decade), lengthened LGP of late rice (1.1±5.4 day/decade) and have little impacts on LGP of single rice (-0.4±5.4 day/decade). ORCHIDEE-crop simulations further show that change in transplanting date caused widespread LGP change only for early rice sites, offsetting 65% of climate-change-induced LGP shortening. The primary drivers of LGP change are thus different among the three types of rice. Management is predominant driver of LGP change for early and single rice. This chapter demonstrated the capability of the optimized crop model to represent complex regional variations of LGP. Future studies should better document observational errors and management practices in order to reduce large uncertainties that exist in attribution of LGP change and to facilitate further data-model integration. In Chapter 4, a harmonized data set of field warming experiments at 48 sites across the globe for the four most-widely-grown crops (wheat, maize, rice and soybean) is combined with an ensemble of gridded global crop models to produce emergent constrained estimates of the responses of crop yield to changes in temperature (ST). The new constraining framework integrates evidences from field warming experiments and global crop modeling shows with >95% probability that warmer temperatures would reduce yields for maize (-7.1±2.8% K-1), rice (-5.6±2.0% K-1) and soybean (-10.6±5.8% K-1). For wheat, ST was less negative and only 89% likely to be negative (-2.9±2.3% K-1). The field-observation based constraints from the results of the warming experiments reduced uncertainties associated with modeled ST by 12-54% for the four crops

As the shortage of fresh water becomes more and more critical, alternative sources are being sought. The reuse of wastewater has become a viable option, particularly for agriculture and landscaping. However, the possible presence of the enteric pathogens, especially viruses, in wastewater has created concern about potential health risks associated with this practice. If wastewater is used for irrigation it may contaminate vegetable crops which are commonly eaten raw. Also, it may contaminate grass used for golf courses, school yards, and playgrounds where more people may be exposed. Rotaviruses may be of particular concern since they are a cause of infantile diarrhea and gastroenteritis in adults and have been a cause of waterborne disease outbreaks. No information, however, is available about the dissemination and survival of rotaviruses on uncooked food and landscaped areas. This information is necessary in developing criteria for determining safe uses of wastewater for crop irrigation. A method was developed for recovery of rotavirus from the surface of vegetables. The simian rotavirus SA-11, adsorbed onto the vegetable surfaces and effects of various eluents, pH, and exposure time, was evaluated to optimize recovery. The maximum recovery of rotavirus occurred with a solution of 3% beef extract at pH 8.0 after 5 minutes of exposure. Survival of rotavirus SA-11 on lettuce, radishes, and carrots stored at 4°C and room temperature was evaluated. Rotavirus SA-11 was able to survive up to 30 days at refrigeration temperatures and up to 25 days at room temperatures. Rotavirus survived longest on lettuce. The survival of coliphage and enteric viruses on grass was studied during winter and summer outdoors. Coliphage, poliovirus, and rotavirus SA-11 survived on two types of grass during winter and summer from 8 to 40 hours. Human rotavirus survived longer than the other enteric viruses, however, coliphage was more sensitive to inactivation. The occurrence of rotaviruses and enteroviruses in the secondarily treated sewage (activated sludge) was evaluated over a one year period. Total coliforms, pH, and turbidity were also determined. Rotavirus concentrations peaked during Spring and Winter while concentrations of enteroviruses peaked during May, September, and December. No correlation was found between the concentrations of total coliforms, rotaviruses and enteroviruses.

Crop coefficients (K(c)) are a useful means of predicting how much water is needed for irrigating a crop. The crop water stress index (CWSI), on the other hand, is a means of knowing when to irrigate. Two field experiments were conducted during the summers of 1990 and 1991 at Maricopa Agricultural Center and Marana Agricultural Center, respectively, to evaluate water use (evapotranspiration, ET) of different cotton varieties, to develop crop coefficients for cotton grown in the state of Arizona, and to evaluate empirical and theoretical crop water stress indices under field conditions. For the 1990 experiment, ET from the cotton variety DPL 77 was obtained using soil water balance (SWB) and steady state heat balance (SSHB) techniques. For the 1991 experiment, ET from two cotton varieties (DPL 20 and Pima S-6) was estimated using the Bowen ratio energy balance (BREB) method and the steady state heat balance method. Reference evapotranspiration (ETᵣ) was obtained from weather stations located close to the experimental plots. Average daily ET from the SSHB measurements ranged from 8.24 to 15.13 mm and from 10.34 to 12.12 mm for the 1990 and 1991 experiments, respectively. Total ET from the SWB was approximately 19% less than the total ET estimated by the SSHB. Total ET from individual plants was well correlated with average stem area over the evaluation periods. Daily ET from the two cotton varieties (DPL20 and Pima S-6) was approximately similar when irrigation conditions were the same, but differed later by as much as 48.4% as irrigation continued for the variety Pima S-6 only. Daily ET from the BREB measurements and ETᵣ were used to develop a crop coefficient curve for cotton grown at Marana, Arizona, which had a maximum smoothed value of 1.21. A critical value of CWSI equal to 0.3 was obtained by observing the pattern of the CWSI values over well-watered and drier conditions, and from previous research. Using the developed crop coefficient curve and the CWSI should provide a useful means of scheduling irrigation for cotton grown under climatic conditions similar to those at Marana, Arizona.

Application of anaerobic swine (Sus scrofa domesticus) lagoon liquid onto cropland by irrigation is a common method of waste disposal and treatment. Currently, the application rate of swine lagoon liquid is based on the N concentration of the lagoon liqu id and the N required by the receiver crop to obtain a realistic yield. In North Carolina, only 50% of the total N in the swine lagoon liquid applied by irrigation is considered available for plant use during the first year after application. Uncertaint y exists as to whether this coefficient accurately predicts the amount of plant-available N. Therefore, research was conducted in the Coastal Plain of North Carolina to determine the efficiency of N uptake by corn (Zea mays L.) and soybean (Glycine max M errill) receiving swine lagoon liquid through irrigation. The line-source sprinkler irrigation method was used to provide a continuous variable N rate, ranging from 0 to 290 kg N/ha, across the field during 1999 and 2000. Ammonia volatilization losses r anged from 6 to 22% during irrigation. Crop yield and grain N recovered were affected more by the amount of liquid than N applied in 1999. Nitrogen recovered in grain in 1999 was <15% for both corn and soybean at 168 kg N/ha of either swine lagoon liqui d or ammonium nitrate. In 2000 at the 168 kg N/ha rate, grain N removal by corn, nonnodulating soybean, and nodulating soybean was 28, 25, and 39% from swine lagoon liquid and 45, 31, and 56% from ammonium nitrate. Based on yields and grain N removed by corn and nonnodulating soybean in 2000, N from applied swine lagoon liquid, accounting for N losses during irrigation, was about 70% as effective as ammonium nitrate. Symbiotic N2 fixation by the soybean was reduced by 60% when applied N reached 175 kg N/ha for both ammonium nitrate and swine lagoon liquid. While nodulating soybean removed more grain N than did either corn or nonnodulating soybean in 2000, soil inorganic N concentrations at the end of the growing season were higher for the nodulating s oybean. Therefore, it is not conclusive if soybean would be a better receiver crop than corn for swine lagoon liquid. Based on the results of this study, using the 50% available N coefficient of the lagoon liquid comes close to predicting plant-availabl e N when N losses during irrigation are around 25%. Nitrogen losses during irrigation can significantly affect plant-available N when applied N is based on the N concentrations of the lagoon liquid.

Irrigation water of poor quality can have deleterious effects on soils. However, the effect of drip irrigation on seasonal and long term (e.g. over 50 years) changes in soil chemical properties is poorly understood, complicated by the two-dimensional water flow patterns beneath drippers. Field and laboratory experiments were conducted, along with computer modelling, to evaluate morphological and physio-chemical changes in a typical Barossa Valley Red Brown Earth (Palexeralf, Chromosol or Lixisol) when drip irrigated under various changing management practices. This work focused on the following two management changes : (i) switching from long-term irrigation with a saline source to less saline water and (ii) gypsum (CaSO₄) application. A literature review (Chapter 1) focuses on the distribution, features, properties and management of Red Brown Earths in the premium viticultural regions of the Barossa Valley and McLaren Vale, South Australia. The effects of irrigation method and water quality on the rate and extent of soil deterioration are emphasised. The review also discusses the irrigation of grapes (Vitis vinifera) and summarises previous research into the effect of sodicity and salinity on grape and wine characteristics. This chapter shows the importance of Red Brown Earths to Australian viticulture, but highlights their susceptibility to chemical and physical degradation. Degradation may be prevented or remediated by increasing organic matter levels, applying gypsum, modifying cropping and through tillage practices such as deep ripping. Chapter 2 provides general information on the two study sites investigated, one in the Barossa Valley and the other at McLaren Vale. Local climate, geology, geomorphology and soils are described. Chapter 3 details laboratory, field and sampling methods used to elucidate changes in soil chemical and physical properties following irrigation. The genesis of the non-irrigated Red Brown Earth in the Barossa Valley is described in Chapter 4, and is inferred from geochemical, soil chemical, layer silicate and carbonate mineralogical data. Elemental gain and loss calculations showed 42% of original parent material mass was lost during the formation of A and A2 horizons, while the Bt1 and Bt2 horizons gained 50% of original parent material mass. This is consistent with substrate weathering and illuviation of clay from surface to lower horizons. The depth distributions of all major elements were similar ; the A horizon contained lower amounts of major elements than the remainder of the profile, indicating this region was intensely weathered. This chapter also compares the non-irrigated site to the adjacent irrigated site (separated by 10 m) to determine if the sites are pedogenically identical and geochemical changes from irrigation. Many of the differences between the non-irrigated and irrigated sites appear to be correlated with variations in quartz, clay, Fe oxide and carbonate contents, with little geological variation between the sample sites. In Chapter 5 morphological, chemical and physical properties of a non-irrigated and irrigated Red Brown Earth in the Barossa Valley are compared. Alternating applications of saline irrigation water (in summer) and non-saline rain water (in winter) have caused an increase in electrical conductivity (EC [subscript se]), sodium adsorption ratio (SAR), bulk density (ρ b) and pH. This has resulted in enhanced clay dispersion and migration. Impacts on SAR and ρ b are more pronounced at points away from the dripper due to the presence of an argillic horizon, which has greatly influenced the variations in these soil properties with depth and distance from the dripper. Dispersion and migration of clay were promoted by alternating levels of EC, while SAR remained relatively constant, resulting in the formation of a less permeable layer in the Bt1 horizon. Clay dispersion (breakdown of micro-aggregate structure) was inferred from reduced numbers of pores and voids, alterations in colouring (an indication that iron has changed oxidation state) and increased bulk density (up to 30 %). Eleven years of irrigation changed the soil from a Calcic Palexeralf (non-irrigated) to an Aquic Natrixeralf (irrigated) (Soil Survey Staff, 1999). These results, combined with data from Chapter 4, were used to develop a mechanistic model of soil changes with irrigation. Chapters 6, 7 and 8 describe field experiments conducted in the Barossa Valley and McLaren Vale regions. This data shows seasonal and spatial variations in soil saturation extract properties ( EC [subscript se], SAR [subscript se], Na [subscipt se] and Ca [subscript se] ). At the Barossa Valley site (Chapter 6) non-irrigated soils had low EC [subscript se], SAR [subscript se], Na [subscript se] and Ca [subscript se] values throughout the sampling period. The irrigated treatments included eleven years of drip irrigation with saline water (2.5 dS / m) and also gypsum application at 0, 4 or 8 tonnes/hectare in 2001 and 2002. Salts in the profile increased with gypsum application rate, with high levels occurring midwinter 2002 prior to rainfall leaching salts. SAR has declined with gypsum application, particularly in the A horizon and at 100 cm from the dripper in the Bt1 horizon ; this has the potential to reflocculate clay particles and improve soil hydraulic conductivity. Chapter 7 presents further results from the Barossa Valley site, this treatment had been irrigated for 9 years with saline water (2.5 dS / m) prior to switching to a less saline water source (0.5 dS / m). The soil also received gypsum at 0, 4 or 8 tonnes / hectare in 2001 and 2002. It was found that the first few years are critical when switching to a less saline water source. EC declines rapidly, but SAR requires a number of years, depending on conditions, to decline, resulting in a period during which the Bt1 horizon may become dispersed. Gypsum application increased the EC [subscipt se] but not to the EC [subscript se] levels of soil irrigated with saline water. Chapter 8 examines soil chemical properties of a McLaren Vale vineyard, irrigated with moderately saline water (1.2 dS / m) since 1987 and treated with gypsum every second year since establishment. This practice prevented the SAR (< 8) rising and a large zone of the soil profile (20 to 100 cm from dripper) has a high calcium level (> 5 mmol / L). However, irrigation caused the leaching of calcium beneath the dripper in both the A and B horizons (0 to 20 cm from dripper) (< 4 mmol / L). Chapters 9 and 10 interpret and discuss results from continuous monitoring of redox potential (Eh) and soil solution composition in the Barossa Valley vineyard, irrigated with saline or non-saline water, and gypsum-treated at 0 and 4 tonnes / hectare. Soil pore water solution (Chapter 9) collected by suction cups is compared to results obtained in chapters 6 and 7. The soil has extended zones and times of high SAR and low EC. This was particularly evident in the upper B horizon, where the SAR of the soil remained stable throughout the year while the EC was more seasonally variable with EC declining during the winter months. The A horizon does not appear to be as susceptible to clay dispersion (compared to the B horizon) because during periods of low EC the SAR also declines, which may be due to the low CEC (low clay and organic matter content) of this horizon. Chapter 10 presents redox potentials (Eh) measured using platinum redox electrodes installed in the A, A2 and Bt1 horizons to examine whether Eh of the profile varies with irrigation water quality and gypsum application. Saline irrigation water caused the B horizon to become waterlogged in winter months, while less saline irrigation water caused a perched watertable to develop, due to a dispersed Bt1 horizon. Application of gypsum reduced the soil Eh particularly in the A2 horizon (+ 500 to + 50 mV) during winter. Thus redox potential can be influenced by irrigation water quality and gypsum applications. Chapter 11 incorporated site data from the Barossa Valley non-irrigated site into a predictive mathematical model, TRANSMIT, a 2D version of LEACHM. This model was used to predict zones of gypsum accumulation during long-term irrigation (67 years). When applied over the entire soil surface, gypsum accumulated at 60 to 90 cm from the dripper in the B horizon; higher application rates caused increased accumulation. When applied immediately beneath the irrigation dripper, gypsum accumulated in a 'column' under the dripper (at 0 to 35 cm radius from the dripper), with very little movement away from the dripper. Also, the zone of accumulation of salts from high and low salinity irrigation water was investigated. These regions were found to be similar, although concentrations were significantly lower with low salinity water. In low rainfall years salts accumulated throughout the B horizon (35 - 150 cm), while in periods of high rainfall (and leaching) the A, A2 and Bt1 horizons (0 - 60 cm) were leached, although at greater depths (80 - 150 cm) salt concentrations remained high. Chapter 12 summarises results and provides an understanding of soil processes in drip irrigated soils to underpin improved management options for viticulture. This study combines results from redox and soil solution monitoring, mineralogy, elemental gains and losses, and seasonal soil sampling to develop a mechanistic model of soil processes, which was combined with computer modelling to predict future properties of the soil. Major conclusions and recommendations of this study include : - Application of saline irrigation water to soil then ameliorated with gypsum - The first application of gypsum was leached by the subsequent irrigation from extended regions of the soil. As Na continues to enter the system via irrigation water, gypsum needs to be regularly applied. Otherwise calcium will be leached through the soil and SAR increases. - Application of non-saline irrigation water to soil then ameliorated with gypsum - The soil was found to only require one application at 8 tons / ha as this reduced SAR sufficiently. As less salt is entering the soil, subsequent gypsum applications can be at a lower rate or less frequently than required for saline irrigation water. - Gypsum applied directly beneath the dripper systems distributes calcium to a narrow region of the soil, while large regions of the soil require amelioration (high SAR) and are not receiving calcium. Therefore, gypsum application through the drip system or only beneath the dripper should be combined with broad acre application. - A range of methods to sample vineyards is recommended for duplex soils, including the use of saturation extracts, sampling time, sampling location (distance from dripper) and depth of sampling. This work is critical for vineyard management and may be applicable to other Australian viticulture regions with Red Brown Earths.
Thesis (Ph.D.) -- University of Adelaide, School of Earth and Environmental Sciences, 2004.

Most land is still state owned and is granted to users through traditional authorities. Even though the government has undertaken some programmes to reduce rural poverty and has initiated land reform programmes, improved service delivery and formed new water rights legislation in rural areas, the problem of low crop production still persists among South African farmers. The study was undertaken to identify different farmers’ aspirations and goals for expanding their crop production from homestead gardening to irrigation plots in Mhlontlo Local Municipality, in the Eastern Cape of South Africa. The central problem is that smallholder farmers are not expanding their scale of crop production even though they have access to natural capital which includes land and water. The broad objective of the study was to determine the aspirations and goals of farmers to expand irrigation crop production from homestead gardens to irrigation plots. The specific objectives of the study were to assess factors that addressed smallholder farmers’ aspirations and goals to expand crop production, to identify challenges that smallholder farmers encountered in expanding from homestead gardens to irrigation plots and to determine the current state of homestead gardens and irrigation plots. A list of 20 goals were identified from the field survey with 54 homestead food gardeners and 50 smallholder irrigation farmers in the different villages of the Mhlontlo Local Municipality. Random sampling was used to select the farmers who were asked to score the identified farm enterprise goals in terms of their relative importance. The goals were categorised into five factors using Gasson goal ranking methods which ranked goals on the basis of intrinsic, expressive, instrumental, and social criteria. The next step was to determine the standard deviations and means of the ranked goals. Descriptive statistics was then used to profile the farmers according to such factors as age, gender, years of farm experience, types of plot, the availability of water and land for crop production, the income farmers generate from the sale of crops produced and these are cross-tabulated with their goal rankings. The Logit model was used to estimate the probability that farmers would belong to a particular goal ranking and performance category. The logit model was also used to identify the factors that influence the expansion of the cropped area. The results revealed that maize production and land size where significant at 1%. Age and type of irrigation used were also positively significant at 1%. The results also revealed that the adoption of agricultural technology by smallholder irrigation farmers and homestead food gardens contributed to better quality produce.

Differential adaptations of barley (Hordeum vulgare L.) and wheat (Triticum spp.) genotypes suggest that they be evaluated under multi-environmental conditions. The objectives of this study were to determine if small grain genotypes, bred for various moisture conditions, respond differently in terms of yield, water use, and rooting pattern to contrasting moisture conditions. Eight small grain genotypes were compared under a gradient of water from 89 to 404 mm (plus 254 mm of stored water) in a field study at Marana, AZ. A barley bred for low input conditions had greater root density in the subsoil and used moisture earlier in the season when compared to a high input barley (WestBred Gustoe). The cultivars bred for high input conditions required more water for optimum yield compared to those bred for low input conditions.

Thesis (MTech (Agriculture))--Cape Peninsula University of Technology.
During the past years government regulations concerning winery effluent became stricter to protect the environment. Wineries are continually improving wastewater management and finding appropriate ways to reduce cellar effluent. Due to water scarcity in South Africa, it could be a huge advantage if winery effluent could be used as irrigation water for vineyards. If the industry can re-use the untreated wastewater, it will not only save a huge amount of irrigation water, but it will also be able to get rid of the vast amount of cellar effluent. Grape production plays a major role in agriculture worldwide. The world production of grapes worldwide in 2013 was 751 MgL. South Africa is the 9th biggest wine producer in the world with 10 X 10HL of wine. In the earlier years of wine production in South Africa, the small volumes of winery wastewater did not have a negative impact on the environment but with the increased volumes over the last years, the possibility of contamination of the soil and the environment has increased. Government decided to regulate the irrigation of cellar effluent with the National Water Act of 1998 as approved by the Department of Water Affairs (DWAF). There are different ways to get rid of cellar effluent. One successful way is by constructed wetlands where plants are used to break down minerals which could be detrimental to the environment. This is a successful way to get rid of cellar effluent but could take up to six weeks before the mineral contents can be broken down by the plants. Another way is to use bio-reactors to break down the contents of the cellar effluent, but this is expensive. Wastewater consists of important nutrients needed for plant growth such as macro-nutrients like N, P, K and micro-nutrients like Fe, Zn, Mn and Cu and a substantial amount of organic matter. If cellar water, just like domestic wastewater is used for irrigation the farmer can save water when he uses less fertiliser, because of the high nutrient content in the cellar effluent. If cover crops such as oats (Avena sativa L. cv. Pallinup) in winter and pearl millet (Pennisetum glaucum (L.) R. Br.) in summer can be used to remove excess cations, as well as unwanted chemicals such as toxic metals from the soil, it may result in effluent water with a higher chemical oxygen demand (COD) level than the current legal limitations that can be used to irrigate the vineyard. The aim of this project was, therefore, to determine the ability of oat and pearl millet cover crop to remove excess minerals from the soil irrigated with augmented water at different COD levels, without a negative effect on growth and yield of the vineyard or wine quality. Field trials were carried out in a Cabernet Sauvignon/99 Richter vineyard established on a sandy soil at the Goudini Cellar near Rawsonville.

Intensive tillage and monoculture cropping practices reduce soil C accumulation hence increasing soil vulnerability to chemical, physical and biological degradation. This study focussed on enhancing biomass production of wheat and oat winter cover crops as a means of increasing C sequestration in the low organic C soils of the central part of Eastern Cape Province. The specific objectives were (i) to evaluate the short-term effects of no till and cereal-fallow based crop rotations on; soil organic matter related parameters, pH and electrical conductivity, (ii) soil bulk density, water retention and aggregate stability, (iii) soil microbial biomass C and N, mineralizable N, soil respiration, and dehydrogenase enzyme activity, (iv) grain yield, soil nutrient concentration (N, P and K) and their uptake by maize, and (v) to identify soil parameters with high sensitivity to tillage under maize-fallow-maize, maize-wheat-maize and maize-oat-maize rotational cover cropping practices. The experiment was laid out as a split-plot arrangement in a randomized complete block design with 4 replicates. Tillage treatments (CT and NT) were applied on the main plots which measured 8 × 18 m while crop rotation treatments were applied in the subplots which measured 8 × 6 m. The rotation treatments were maize-fallow-maize (MFM), maize-wheat-maize (MWM) and maize-oat-maize (MOM). Weed control in NT plots involved preplant application of glyphosate to control mainly the grass weeds while post emergence weed management was done using Atrazine (485 atrazine and 15 g l-1 triazines). Initial weed control in CT plots was achieved through ploughing to a depth of 20 cm followed by disking while post emergence weed iii management was done by hand hoeing. Soil parameters measured were; (i) particulate organic matter (POM), soil organic carbon (SOC), total nitrogen (TN), pH and electrical conductivity (EC), (ii) soil bulk density (b), moisture at field capacity (FC), aggregate mean weight diameter (MWD) determined by fast wetting (FW), slow wetting (SW), mechanical breakdown by shaking (MB) and the stability index (SI), (iii) soil microbial biomass C (MBC) and N (MBN), mineralizable N (MN), soil respiration (SR), and dehydrogenase enzyme activity (DHEA). No-till increased POM and TN compared to CT in Lenye and Burnshill, respectively. The MWM and the MOM rotations increased TN relative to the MFM rotation in Lenye. The MWM and MOM rotations enhanced SOC relative to MFM in all sampled soil depths at Burnshill and similar observations were made under MOM rotation in the 5-20 cm depth in Lenye. The MWM and MOM rotations tended to depress soil pH relative to the MFM rotation in both sampled soil depths in Lenye while NT reduced soil pH relative to CT on the surface soil layer in Burnshill. Soil EC and pH varied with depth across tillage practices but both parameters remained within the ideal range for successful crop production over the study period. Soil stability index (SI) and aggregate MWD determined by FW, SW and MB were higher in Lenye compared to Burnshill. The MOM rotation enhanced the SI relative to MFM and MWM rotations at both sites. Scanning electron microscope (SEM) showed that more organic C was incorporated into the soil under NT and MOM rotation compared to CT and MFM rotation which had few organic coatings on the soil particles. Microbial properties varied with plant biomass input as influenced by tillage and type of rotational cover crop at both sites. Like in other past studies, NT showed higher levels of MBC, MBN, NM and SR at the soil surface layer compared to CT in Burnshill. No till increased MN iv relative to CT in both sampled soil depths in Lenye and resulted in higher DHEA compared to CT in Burnshill. The MOM rotation increased MBC, MBN, MN relative to MFM rotation especially within surface soil layer. Similar observations were made with respect to MN and SR in both sampled soil layers at Lenye. By contrast, the DHEA was higher under the MFM relative to the MWM and MOM rotations in Lenye but similar under the MFM and MOM rotations in Burnshill. Maize grain yield was not affected by both tillage and crop rotations but varied with cropping season. Comparable grain yields observed under the two tillage practices with similar fertilizer application rates indicated the advantage of NT over CT in saving on labour costs in maize production without compromising yields. High plant biomass retention under NT relative to CT contributed to high soil N and P levels under the former compared to the latter tillage practice especially on soil surface layer at both study sites. Principal component analysis (PCA) revealed that soil chemical and biological parameters closely linked to organic matter, namely SOC, MN, MBC and MBN showed the highest sensitivity to tillage and crop rotation treatments. Soil aggregate MWD determined by SW and b were the physical parameters which were highly altered by agronomic management practice. The MWM and MOM rotations were clustered together and clearly separated from the MFM rotation and this observed trend only applied to the 0-5 and 5-20 cm depths in Lenye site only. No till, MWM and MOM rotations enhanced POM, SOC and TN relative to CT and MFM rotation suggesting these practices have greater potential to improve soil chemical properties compared to intensive tillage and maize monoculture based production practices. Reduced soil b under MOM rotation and improved SI under NT compared to MFM and CT, respectively v indicate that these practices have the potential to improve degraded soils. Although not significantly different, NT values for MBC, MBN, MN, SR and DHEA were higher compared to CT indicating the potential of the practice to improve soil biotic activity relative to conventional tillage practices. No till enhanced surface soil nitrate N and extractable P compared to CT at both sites revealing the long-term potential of NT in improving the supply of these essential plant nutrients compared to CT. Principal component analysis showed that SOC, MN, K, P, MBC, MBN, soil aggregate MWD determined by SW and b were the most sensitive parameters to tillage and crop rotations. Therefore, these parameters could constitute the minimum data set for assessments of the impact of selected CA practices on soil quality attributes.

El estudio se centra detectar los cambios temporales sufridos en la composición florística de las comunidades de malas hierbas de los cultivos de regadío y en descifrar los factores intrínsecos y extrínsecos subyacentes al éxito de las especies exóticas en estos cultivos y a su capacidad de colonizar los hábitats naturales adyacentes. Se ha utilizado una aproximación funcional. Los resultados muestran que a largo plazo, ha habido cambios en la diversidad, la composición y la estructura funcional de las comunidades de malas hierbas y un incremento del protagonismo de las malas hierbas exóticas. En los cultivos frutales, entre los atributos funcionales más beneficiados destacan la vía fotosintética C4, las formas graminoides y perennes y la capacidad de reproducción vegetativa, así como la hidrocoria y las semillas adaptadas a más de un modo de dispersión. Estos atributos se encuentran representados principalmente en las especies exóticas y su selección está determinada fundamentalmente por el sistema de riego por inundación. Por otro lado, el manejo de los cultivos regados por goteo configura una comunidad de malas hierbas caracterizada por una menor prominencia de especies exóticas y una estructura funcional que la hace menos competitiva hacia los árboles frutales. Los atributos favorecidos en los cultivos frutales regados por inundación se relacionan con la capacidad de las malas hierbas exóticas para colonizar los ambientes riparios adyacentes a los cultivos.
L'estudi es centra a detectar els canvis temporals de la composició florística de les comunitats de males herbes dels cultius de regadiu i a desxifrar els factors intrínsecs i extrínsecs subjacents a l’èxit de les espècies exòtiques en aquests cultius i a la seva potencial capacitat de colonitzar els hàbitats naturals dels voltants. S’ha utilitzat una aproximació funcional. Els resultats mostren que a llarg termini, ha hagut canvis en la diversitat, la composició i l’estructura funcional de les comunitats de males herbes a més d’un increment del protagonisme de les males herbes exòtiques. Als fruiters, entre els atributs funcionals més beneficiats destaquen la via fotosintètica C4, les formes graminoides i perennes i la capacitat de reproducció vegetativa, així com la hidrocòria i les llavors adaptades a més d’un mode de dispersió. Aquests atributs es troben representats principalment a les espècies exòtiques i la seva selecció està dirigida fonamentalment pel sistema de regadiu per inundació. Per altra banda, el maneig dels cultius regats per degoteig configura una comunitat de males herbes caracteritzada per una menor prominència d’espècies exòtiques i una estructura funcional que la fa menys competitiva envers els arbres fruiters. Els atributs que es veuen afavorits en els fruiterars irrigats per inundació també es troba relacionat amb la capacitat que tenen les males herbes exòtiques per colonitzar els ambients riparis adjacents als cultius.
This study aims at identifying temporal changes in weed community composition as well as unravelling the intrinsic and extrinsic factors that lay behind the success of alien weeds in irrigated crops and their potential capability to spread and colonize surrounding natural habitats. These main goals were addressed using a trait-based approach. Results showed that at long-term temporal scale, there were changes in diversity, composition and functional structure of weed communities, accompanied by a higher prominence of alien plants within these weed assemblages. In orchards, C4 photosynthesis, graminoid and perennial forms, clonal reproduction, hydrochory and seed dispersed by multiple methods were among the most benefited plant traits, which were mainly found in successful alien weeds. This trait selection was mainly driven by flood irrigation. On the other hand, management in drip-irrigated orchards configures a weed community characterized by a lower prominence of alien species and a functional structure that make it less competitive to the trees.Furthermore, the trait syndrome favoured in flood-irrigated orchards was also linked to the capacity of alien species to overcome ecosystems filtering and colonize surrounding natural riparian habitats.

Although several studies have investigated on commercial farmers’ risk preferences, there is still lack of information on the risk attitudes and risk preferences of smallholder farmers in South Africa. Risks associated with the adoption of new agricultural technology need to be explored in order to address the transition from homestead food gardening to smallholder irrigated farming. This study seeks to understand risk perception of smallholder irrigation farmers by linking constraints to commercialisation, adoption of new agricultural technologies and risk preferences of smallholder farmers in the former Ciskei Homelands of the Eastern Cape. A total of 101 respondents were surveyed, consisting of 38 smallholder farmers and 63 homestead food gardeners in the Eastern Cape. Questionnaires were used to record household activities, socio-economic and institutional data as well as household demographics through personal interviews. The probit results indicated that older farmers are less risk averse thus more willing to take risk. The risk analysis indicates that farmers who are employed elsewhere are more willing to take risk as income is playing a major role in risk preferences. The results also prove that factors such as tenure system and years in farming have a major influence on farmers’ decision to take risk and adopt new agricultural technology. According to the multi-logit model the major factors influencing technology adoption and risk taking are household size, water rate and type of irrigation system used by the farmers. This study provides useful practical insights for policy makers, farm advisers and researchers in the design of effective and efficient policies, programmes and projects which can affect the adoption of technology, increase smallholder farmers capacity to manage risk and drive growth in the food market.

A inovação tecnológica é o caminho mais viável para desenvolver uma agricultura sustentada no Brasil. Portanto, o país deve investir nos setores que possam produzir tecnologias inovadoras, adequadas as suas condições peculiares e de custo mais acessível, em substituição à dependência por produtos importados. Dentro desse contexto, este trabalho tem os objetivos de desenvolver anteparos de microaspersor com boa uniformidade de distribuição para trabalhar com sobreposição e adaptar a técnica desenvolvida por Almeida, Botrel e Smith (2008) para os microaspersores convencionais. O trabalho foi conduzido no Laboratório de Hidráulica e na área experimental do Departamento de Engenharia Rural da ESALQ/USP, onde foram desenvolvidos e avaliados os protótipos de microaspersores, e avaliado o desempenho da adaptação do microtubo aos microaspersores comerciais. Para o desenvolvimento dos protótipos de microaspersores foram testados diversos materiais e processos. Os materiais utilizados foram argila, gesso, biscuit, massa de modelar, pedra talco e os tarugos de PVC, technyl, teflon e polipropileno. Já os processos foram o torneamento mecânico, modelagem e a prototipagem rápida. O desempenho da adaptação dos microtubos aos microaspersores comerciais foi avaliado através de testes em laboratório e no campo. A relação comprimento de microtubo versus pressão de operação versus vazão foi determinada, em seguida, avaliou-se a uniformidade de distribuição de água na linha lateral. Utilizou-se os coeficientes de uniformidade de Christiansen, o da uniformidade de distribuição e o da uniformidade estatística na avaliação do desempenho dos emissores. O PVC e o tecnyl foram os materiais que apresentaram mais facilidade na construção das bailarinas, porém, o PVC foi o escolhido devido ao melhor acabamento. As melhores sobreposições ocorreram com o protótipo de 6 canaletas com 350 e duas canaletas diferenciadas. Os ajustes realizados nos protótipos iniciais que não funcionaram contribuíram significativamente para que o protótipo desenvolvido alcançasse resultados positivos. A geometria das bailarinas, ângulo e número de canaletas afetaram o desempenho do modelo, sendo que, os de maiores ângulos apresentaram uniformidade de distribuição de água mais satisfatórias. A utilização da técnica de microtubos se adapta a microaspersores convencionais, uniformizando a vazão ao longo da linha lateral.
The technology innovation is the way most feasible to develop a sustainable agriculture in Brazil. In this way, the country will have to invest in sectors which can produce innovation technologies, adequate to specific conditions and with cost more accessible, to replace the dependency from imported products. In this context, this work had to objective to develop microsprinkler spinner deflector with good distribution uniformity to work with overlap and adapt the microtubes techniques developed by Almeida, Botrel e Smith (2008) to commercial microsprinkler. Experiments in laboratory and field were carried out at Escola Superior de Agricultura Luiz de Queiroz, University of Sao Paulo, Brazil, where were developed and evaluated the microsprinkler prototypes and evaluated discharge uniformity along of lateral line with commercial micro-sprinklers and microtubes as emitter. In the development of the microsprinkler prototypes were tested a lot of materials and processes. The materials utilized were clay, biscuit, plaster, modeling mass, talc stone, PVC, technyl, teflon and polypropylene. The processes were mechanic tournament, modeling and the rapid prototyping. The performance of micro-sprinkler irrigation system with microtube emitters was evaluated both laboratory and field tests. Microtube pressure-length-discharge relationship was determinate and discharge distribution uniformity along of lateral line was evaluated. Uniformity Coefficient from Christiansen (CUC), Distribution Uniformity (DU) and Uniformity Statistic (Us) were used as indicators for evaluation of performance of emitters. Among the tested materials, the PVC and the technyl showed more facility in the deflector build, however, the PVC was choose due the better finish small channels. The rapid prototyping process provided the better finish in the deflector. In the proposed overlap, the better overlap arrangement occurred with the prototype of 6 channels with 350 and two channels differentiated. The developed prototypes which not worked and the adjustments did in them, contributed significantly to reach positive results in prototypes. The deflector geometric, angle and number of channels affected directly the performance of microsprinklers, nevertheless, the biggest angle showed water distribution uniformity more satisfactory. The utilization of microtubes techniques adapted well in conventional microsprinklers, and provided good uniformity in the discharge in lateral line.

Achieving high biomass yields of cover crops has been a challenge to the success of Conservation Agriculture (CA) practices in the Eastern Cape (EC). A study was conducted to evaluate strategies for optimizing cover crop biomass production. Trials were carried out to screen summer and winter cover crops, as well as evaluate intercropping patterns and planting dates for biomass, weed suppression and subsequent maize yield under irrigation. Four summer legume cover crop species were evaluated under a Randomised Complete Block Design (RCBD) design. The cover crops were fertilized with 13.34 kg ha-1 of N, 20 kg ha-1 P and 26.66 kg ha-1 K. In the 2008/09 summer season a maize crop was superimposed on the 2007/08 screening trial under no-till. The crop was fertilized with 60 kg ha-1 of N. An intercropping trial was conducted over two seasons as a way of investigating the best way of incorporating cover crops into farmers cropping systems. This was done bearing in mind the limitation of resources such as land. The trial evaluated 3 factors laid as a 2 x 2 x 3 factorial arranged in a split-plot design. The main factor was cover crop planting date (planting at maize planting or 2 weeks after maize planting). The sub plot factor was intercropping pattern (strip intercropping and between row intercropping). A trial was also conducted to evaluate the effect of planting date (End of April and mid May) and four winter legume cover crop species on cover crop biomass, weed suppression and maize grain yield. The experiment was laid out as a Randomised Complete Block Design (RCBD) replicated 3 times. In the subsequent summer season a maize crop was superimposed on the winter trial to test the residual effects of the cover crop species. Another study was conducted to evaluate winter cereal cover crop species for biomass accumulation, weed suppression and subsequent maize grain yield. The cover crops as well as a weedy fallow control plot treatments were laid out as a Randomised Complete Block Design replicated 3 times. In the subsequent summer season a maize crop was superimposed on the site under no-till to evaluate the residual effect of the cover crops on maize. The results showed sunhemp, cowpea and lablab as the best cover crops with high biomass and weed suppression whilst mucuna was the least. Sunhemp consistently yielded higher cover biomass averaging 11200 kg ha-1 over the two seasons whilst mucuna had a consistently lowest average biomass yield of 4050 kg ha-1. These cover crops were above the critical 6 t ha-1 for effective weed suppression. There was a significant (p<0.01) relationship of cover crop dry weight and weed dry weight in both seasons. Subsequent maize grain yield was significantly higher in the sunhemp plots (64.2 %) than the weedy fallow plot. Mucuna, lablab and cowpea had maize grain yield increases of 16.6%, 33% and 43.2% respectively. Intercropping cover crops at maize planting yielded higher cover crop dry weights than a delay in intercropping cover crops. A delay in intercropping resulted in significantly higher average maize grain yield of 4700 kg ha-1 compared to intercropping at maize planting (3800 kg ha-1) and sole maize (4300 kg ha-1) over the two seasons. Strip intercropping also yielded higher (5000 kg ha- 1) average maize grain yield compared to row intercropping (3600 kg ha-1) and sole maize (4300 kg ha-1). There was a significant (p<0.05) relationship between cover crop dry weight in the 2007/08 season and maize grain yield in the 2008/09 season. Early planting grazing vetch gave the highest biomass yield of 8100 kg ha-1 whilst early planted red clover had the lowest biomass of 635 kg ha-1. Low weed dry weights were also obtained from the early planted grazing vetch as opposed to the other treatments. There was a significant (p<0.001) relationship of cover crop dry weight and weed dry weight. In the subsequent 2008/09 summer season early planted grazing vetch had the highest maize yield of 7500 kg ha-1 which was 56.3 % more than the weedy fallow plot had 4800 kg ha-1. The weedy fallow plot also had high weed infestation than the cover crop plots. There were significant (p<0.01) relationships between cover crop dry weight and maize grain yield, winter weed dry weight and maize grain yield and summer weed dry weight and maize grain yield. The results also showed triticale (13900 kg ha-1) as the best winter cover crop for biomass production. Italian ryegrass (6500 kg ha-1) produced the least amount of biomass. In The subsequent maize crop white oats gave highest maize grain yield (6369 kg ha-1) which was 33 % more than the weedy fallow plot (4784 kg ha- 1). There were also significant (p< 0.01) relationships of maize grain yield and winter weed dry weight, maize grain yield and summer growing weeds. The various studies demonstrated that there is opportunity for high biomass production under small scale farmers irrigated conditions using cover crops both in winter and summer. Best bet cover crops were sunhemp, cowpea and lablab for summer and triticale, white oats, barley, Italian ryegrass and grazing vetch for winter. Cover crops can also be incorporated into farmers cropping systems as sole crops or intercrops within the maize based cropping systems. Strip intercropping can be used by farmers as a way of introducing cover crops. Critical to achievement of high biomass is the time of planting cover crops with high biomass when planting is done early. A 2 week delay in strip intercropping cover crop into maize can be used as a way of incorporating cover crops into farmers cropping systems with minimal maize yield reduction.

L'utilisation des eaux usées dans l’agriculture à des fins d'irrigation et de fertilisation n'est pas une pratique récente. Cependant, au cours de ces deux dernières décennies, cette pratique a suscité un intérêt croissant au regard des risques potentiels qu’elle représente pour la santé humaine. Outre les nutriments utiles et la matière organique que ces eaux introduisent dans les terres agricoles, des produits pharmaceutiques (PhACs) et d’autres micropolluants organiques sont également co-introduits, conduisant à la présence de composés chimiques indésirables dans les agroécosystèmes, plus remarquablement dans les cultures destinées à la consommation humaine. Des efforts incroyables ont été faits au cours des deux dernières décennies pour analyser ces contaminants dans des échantillons environnementaux, mais il y a encore un manque de méthodes analytiques robustes pour l'extraction et la quantification des multiples micropolluants organiques présents dans des matrices complexes comme les sols et les végétaux, et un manque de connaissances concernant leur devenir dans les agroécosystèmes. Dans ce contexte, le premier objectif de cette thèse est de développer des méthodologies analytiques robustes pour analyser de nombreux micropolluants organiques présents dans les eaux usées, particulièrement les PhACs et leurs métabolites dans le sol et les racines/feuilles de laitue et poireau. Ces méthodes sont basées sur QuEChERS suivies d'une détection par LC-HRMS-QTOF. Des bons taux de récupérations ont été obtenus pour les 48 composés étudiés dans toutes les matrices (en général entre 80 et 120% pour la plupart des composés). La comparaison des deux modes d'acquisition récemment développés, high-resolution multiple reaction monitoring et Sequential Window Acquisition of All Theoretical Fragment-Ion Spectra ont donné des résultats similaires, bien que la MRMHR ait donné des résultats plus cohérents pour la plupart des composés. Enfin, des limites de détection et de quantification satisfaisantes ont été obtenues pour les 3 matrices (par exemple, 0,01 à 0,12 ng/g et 0,04 à 0,38 ng/g poids sec ont été obtenus par les feuilles de laitue, respectivement)L'objectif suivant consiste à appliquer ces méthodologies analytiques pour suivre le comportement et devenir de certains micropolluants sur un champ agricole irrigué avec des eaux usées domestiques traitées. Le deuxième objectif nous a donc permis de comprendre leur distribution dans le sol et les cultures en calculant des facteurs de bioconcentration, en discriminant leur dégradation dans le sol à celle dans les plantes, ceci afin d'évaluer le risque potentiel pour la consommation humaine de végétaux irrigués avec des eaux usées traitées. Deux années successives de culture de laitue et poireau sous serre ont été mises en œuvre, et irrigués goutte à goutte avec différents types d'eau, principalement les eaux usées domestiques traitées. Une faible accumulation dans le sol et les végétaux a été constatée, ce qui s'explique par leur dégradation intensive dans le sol et la plante. Quelques métabolites ont été détectés dans les feuilles de laitue, en particulier la carbamazépine-époxyde issue du métabolisme de la carbamazépine par la plante. Enfin, cette étude a révélé un risque minimum pour la santé humaine lié à la consommation de légumes crus irrigués avec des eaux usées traitées. Le dernier objectif est d'étudier le devenir de certains contaminants introduits dans le sol par l'irrigation des eaux usées, lorsqu'ils sont exposés aux champignons filamenteux du genre Trichoderma omniprésents dans le sol. Des expériences mises en œuvre en milieu liquide ont révélé pour la première fois une capacité importante des espèces de Trichoderma (T. harzanium et T. asperellum) à dégrader deux antibiotiques (ciprofloxacine et ofloxacine) et un fongicide (climazole). Tout aussi important, de nouveaux métabolites de l'ofloxacine et du climbazole ont été identifiés pour la première fois
The use of wastewater in agricultural sector for irrigation and fertilization purposes is not a recent practice. However, until the past couple decades this practice has been of increasing interest regarding the global safety, particularly human health. Besides to the useful nutrients and organic matter that wastewater introduces to the agricultural lands, pharmaceutical active compounds (PhACs) and other organic micropollutants are also co-introduced leading to the presence of undesired chemicals in agroecosystems, most remarkably in crops intended for human consumption. Incredible effort has been made in last couple decades to analyze such contaminants in environmental samples, yet there is still a lack of robust analytical methods for the extraction and quantification of a large number of PhACs and other wastewater pollutants, and a lack of knowledge regarding their fate and behavior in the entire agroecosystem including soil and crops.In this context, the first objective of this thesis was to develop robust and sensitive analytical methodologies specific to soil and crops matrices (e.g., root and leave) to analyze a large number of wastewater organic contaminants mainly PhACs and their metabolites. QuEChERS-based methods followed by detection and quantification on high-resolution mass spectrometry were successfully developed for soil, lettuce/leek root and lettuce/leek leaves. Good recoveries were obtained for the 48 studied compounds in all matrices (in general between 80 and 120 % for most of the compounds). Detection and quantification of compounds was performed on a high-resolution mass spectrometry on quadrupole-time of flight (Q-TOF) coupled to liquid chromatography provided from SCIEX technology. Comparing the two recently developed acquisition modes high-resolution multiple reaction monitoring (MRMHR) and Sequential Window Acquisition of All Theoretical Fragment-Ion Spectra (SWATH) gave similar results, though MRMHR gave more consistent results for most of the compounds. Finally, satisfying detection and quantification limits were obtained for all 3 matrices, for instance lettuce leaves matrix in MRMHR acquisition gave detection limits ranging from 0.01 to 0.12 ng/g and quantification limits ranging from 0.04 to 0.38 ng/g dry weight (d.w).Later, the following objective was to apply these methodologies on real agricultural field irrigated with local treated domestic wastewater. The second objective allowed us to understand the distribution of selected contaminants in soil and crops and calculate their bioconcentration factors, to discriminate their degradation in soil and crops, and finally to assess the potential risk for human consumption of wastewater irrigated crops. Two years of successive growth cycles of lettuce and leek under greenhouse field conditions were successfully implemented. Different kinds of water were used for irrigation mainly domestic treated wastewater, following real drip irrigation conditions. Little accumulation in soil and crops was found, which was explained by the intensive degradation of contaminants in soil and metabolism in crops. A few metabolites were detected in lettuce leaves, particularly carbamazepine-epoxide which was produced by the lettuce metabolism. Finally, this study revealed a de minimis human health risk related to the consumption of raw vegetable irrigated with treated wastewater.The last objective was to study the fate of selected contaminants introduced in soil by wastewater irrigation, when they are exposed to the ubiquitous filamentous soil fungi Trichoderma. Implemented experiments in liquid medium revealed for the first time an important ability of Trichoderma species, namely T. harzanium and T. asperellum to degrade two fluoroquinolones antibiotics (ciprofloxacin and ofloxacin), and one fungicide (climbazole). Equally important, new metabolites of ofloxacin and climbazole were tentatively identified in this study for the first time

Cette étude présente un modèle biophysique de fonctionnement de culture capable de traduire la dynamique de l'évolution de tout couvert végétal, sous différentes conditions abiotiques du milieu (température, eau et rayonnement) mais aussi de sols et de climats. L'approche développée pour le suivi de la cinétique de croissance et de développement des couverts reste très proche de la réalité physiologique de leurs fonctionnements mais aussi de celle liée aux interventions humaines qui se trouve alors compatible avec l'échelle de notre modélisation. Alors que l'utilisation d'une simple loi linéaire d'action de la température par les modèles de fonctionnements des cultures permet de prendre en partie l'effet de l'action de la température sur une gamme assez limitée de température active des espèces végétales, l'approche, assez originale, adoptée dans ce modèle permet l'utilisation d'une vraie loi d'action de la température sur les différents processus biologiques liés au développement et à la croissance, valable sur toute la gamme des températures biologiquement actives. Aussi, cette approche très générique permet de suivre la cinétique des vitesses d'évolution de toutes entités d'une plante, quelque que soit l'espèce ou la variété, et de travailler à n'importe quelle échelle de temps (jour, heure). L'adaptation du modèle logistique (largement utilisé pour décrire les processus biologiques) au contexte physiologique des plantes a permis une description assez originale de la dynamique de la croissance en fonction du développement, prenant en compte à tout moment l'effet d'une contrainte du milieu et sa rétroaction sur la dynamique d'évolution du couvert. La régulation de la croissance a été possible dans ce modèle de développement-croissance à travers la modulation de sa vitesse de croissance (processus le plus sensible au stress) en fonction de deux stress les plus importants chez les végétaux, soit l'eau et le rayonnement. A partir d'un petit nombre de paramètres facilement abordable en bibliographie, il est possible de caractériser la dynamique d'évolution de tout type de couvert végétal évaluant en conditions de sol et de climat variés. Couplé au modèle de bilan hydrique Bilhyna, ce dernier est capable de fonctionner sous différentes situations du milieu, conditions pluviales limitantes notamment, et de gérer ainsi le manque d'eau avec des apports possibles par irrigation de complément où limitées aux besoins tout au long de la croissance intègre alors la rétroaction d'une contrainte du milieu sur la dynamique de l'évolution du couvert. Pour étudier notre modèle, nous avons confronté dans un premier temps les sorties du modèle de loi d'action de la température sur les vitesses de développement aux résultats expérimentaux concernant les cultures du Lin, du maïs et du blé, issus de plusieurs travaux d'auteurs assez connus et tirés de la bibliographie. La confrontation des résultats modèle-mesures a donné des résultats très satisfaisants. Nous avons dans une seconde partie confronté les sorties de l'ensemble du modèle biophysique couplé à bilhyna aux mesures expérimentales que nous avons réalisé au champ sur une période de cinq années, et portant sur deux cultures : le sorgho et du blé. Nous avons ainsi suivi l'évolution de la dynamique de ces couverts à travers leurs trois composantes (LAI, la hauteur du couvert et la profondeur de ses racines) de même que celle des stocks d'eau du sol durant toute la période de la croissance des cultures. Les résultats de la confrontation des sorties du modèle avec les mesures expérimentales ont été assez satisfaisants. [Suite et fin du résumé dans la thèse].

L'optimisation de la gestion de l'eau en agriculture est essentielle dans les zones semi-arides afin de préserver les ressources en eau qui sont déjà faibles et erratiques dues à des actions humaines et au changement climatique. Cette thèse vise à utiliser la synergie des observations de télédétection multispectrales (données radar, optiques et thermiques) pour un suivi à haute résolution spatio-temporelle des besoins en eau des cultures. Dans ce contexte, différentes approches utilisant divers capteurs (Landsat-7/8, Sentinel-1 et MODIS) ont été developpées pour apporter une information sur l'humidité du sol (SM) et le stress hydrique des cultures à une échelle spatio-temporelle pertinente pour la gestion de l'irrigation. Ce travail va parfaitement dans le sens des objectifs du projet REC "Root zone soil moisture Estimates at the daily and agricultural parcel scales for Crop irrigation management and water use impact: a multi-sensor remote sensing approach" (http://rec.isardsat.com/) qui visent à estimer l'humidité du sol dans la zone racinaire (RZSM) afin d'optimiser la gestion de l'eau d'irrigation. Des approches innovantes et prometteuses sont mises en place pour estimer l'évapotranspiration (ET), RZSM, la température de surface du sol (LST) et le stress hydrique de la végétation à travers des indices de SM dérivés des observations multispectrales à haute résolution spatio-temporelle. Les méthodologies proposées reposent sur des méthodes basées sur l'imagerie, la modélisation du transfert radiatif et la modélisation du bilan hydrique et d'énergie et sont appliquées dans une région à climat semi-aride (centre du Maroc). Dans le cadre de ma thèse, trois axes ont été explorés. Dans le premier axe, un indice de RZSM dérivé de LST-Landsat est utilisé pour estimer l'ET sur des parcelles de blé et des sols nus. L'estimation par modélisation de ET a été explorée en utilisant l'équation de Penman-monteith modifiée obtenue en introduisant une relation empirique simple entre la résistance de surface (rc) et l'indice de RZSM. Ce dernier est estimé à partir de la température de surface (LST) dérivée de Landsat, combinée avec les températures extrêmes (en conditions humides et sèches) simulée par un modèle de bilan d'énergie de surface piloté par le forçage météorologique et la fraction de couverture végétale dérivée de Landsat. La méthode utilisée est calibrée et validée sur deux parcelles de blé situées dans la même zone près de Marrakech au Maroc. Dans l'axe suivant, une méthode permettant de récupérer la SM de la surface (0-5 cm) à une résolution spatiale et temporelle élevée est développée à partir d'une synergie entre données radar (Sentinel-1) et thermique (Landsat) et en utilisant un modèle de bilan d'énergie du sol. L'approche développée a été validée sur des parcelles agricoles en sol nu et elle donne une estimation précise de la SM avec une différence quadratique moyenne en comparant à la SM in situ, égale à 0,03 m3 m-3. Dans le dernier axe, une nouvelle méthode est développée pour désagréger la MODIS LST de 1 km à 100 m de résolution en intégrant le SM proche de la surface dérivée des données radar Sentinel-1 et l'indice de végétation optique dérivé des observations Landsat. Le nouvel algorithme, qui inclut la rétrodiffusion S-1 en tant qu'entrée dans la désagrégation, produit des résultats plus stables et robustes au cours de l'année sélectionnée. Dont, 3,35 °C était le RMSE le plus bas et 0,75 le coefficient de corrélation le plus élevé évalués en utilisant le nouvel algorithme
Optimizing water management in agriculture is essential over semi-arid areas in order to preserve water resources which are already low and erratic due to human actions and climate change. This thesis aims to use the synergy of multispectral remote sensing observations (radar, optical and thermal data) for high spatio-temporal resolution monitoring of crops water needs. In this context, different approaches using various sensors (Landsat-7/8, Sentinel-1 and MODIS) have been developed to provide information on the crop Soil Moisture (SM) and water stress at a spatio-temporal scale relevant to irrigation management. This work fits well the REC "Root zone soil moisture Estimates at the daily and agricultural parcel scales for Crop irrigation management and water use impact: a multi-sensor remote sensing approach" (http://rec.isardsat.com/) project objectives, which aim to estimate the Root Zone Soil Moisture (RZSM) for optimizing the management of irrigation water. Innovative and promising approaches are set up to estimate evapotranspiration (ET), RZSM, land surface temperature (LST) and vegetation water stress through SM indices derived from multispectral observations with high spatio-temporal resolution. The proposed methodologies rely on image-based methods, radiative transfer modelling and water and energy balance modelling and are applied in a semi-arid climate region (central Morocco). In the frame of my PhD thesis, three axes have been investigated. In the first axis, a Landsat LST-derived RZSM index is used to estimate the ET over wheat parcels and bare soil. The ET modelling estimation is explored using a modified Penman-Monteith equation obtained by introducing a simple empirical relationship between surface resistance (rc) and a RZSM index. The later is estimated from Landsat-derived land surface temperature (LST) combined with the LST endmembers (in wet and dry conditions) simulated by a surface energy balance model driven by meteorological forcing and Landsat-derived fractional vegetation cover. The investigated method is calibrated and validated over two wheat parcels located in the same area near Marrakech City in Morocco. In the next axis, a method to retrieve near surface (0-5 cm) SM at high spatial and temporal resolution is developed from a synergy between radar (Sentinel-1) and thermal (Landsat) data and by using a soil energy balance model. The developed approach is validated over bare soil agricultural fields and gives an accurate estimates of near surface SM with a root mean square difference compared to in situ SM equal to 0.03 m3 m-3. In the final axis a new method is developed to disaggregate the 1 km resolution MODIS LST at 100 m resolution by integrating the near surface SM derived from Sentinel-1 radar data and the optical-vegetation index derived from Landsat observations. The new algorithm including the S-1 backscatter as input to the disaggregation, produces more stable and robust results during the selected year. Where, 3.35 °C and 0.75 were the lowest RMSE and the highest correlation coefficient assessed using the new algorithm

The current interest in conservation agriculture (CA) technologies is a result of the need to reduce excessive land degradation in most crop producing areas as well as to enhance sustainable food production. Cover crops that are usually grown under CA to provide soil cover, may offer secondary benefits, depending on the farming system. The concept of growing cover crops is a relatively new phenomenon to smallholder farmers. Production of large biomass yields and weed suppression from cover crops were major challenges affecting success and uptake of CA technologies by smallholder irrigation farmers. Coupled with this, low soil fertility limit maize productivity and reduce water use efficiency on smallholder irrigation schemes in what is largely a water strained agro-ecology in South Africa. While cover cropping can increase maize productivity, benefits of different types of mulch are not well understood, leading to challenges in selecting the most appropriate cover crop species to grow in the Eastern Cape Province (EC) of South Africa (SA) which has a warm temperate climate. With respect to any new technology, smallholder farmers are more interested in the economic benefits. Cover crops have been defined as leguminous or non-leguminous plants used for ground cover in various temporal and special configurations used in crop or animal production systems. The purpose of these cover crops is to improve on or more of the following: soil erosion, availability and cycling of N, P, K, Ca and other nutrients, soil moisture and water infiltration, and weed or pest control (Eilitta et al., 2004).. Improvement of animal or human diet may be additional goals. This definition accommodates diverse systems which may include intercrop and sole-cropping systems. In the Eastern Cape Province of South Africa, a government initiative has promoted the growing of winter cover crops in smallholder irrigation schemes (Allwood, 2006). In other parts of Africa, legume food crops have been simultaneously grown with cereal staples to improve both soil cover and human diet (Eilitta et al., 2004). Winter experiments were undertaken in 2007 and 2008 to evaluate biomass accumulation, C and N uptake, weed suppression and response to fertilization. Winter cover crops planted included; oats (Avena sativa), grazing vetch (Vicia dasycarpa), faba bean (Vicia faba), forage peas (Pisum sativum) and lupin (Lupinus angustifolius). After cover crops were terminated, the effects of residues on weeds, fertility, moisture conservation and maize productivity were undertaken in the 2007/08 and 2008/09 summer seasons. Field studies were also done in the 2007/08 and 2008/09 summer seasons to investigate effects of strip intercropping patterns (3:2; 4:2; and 6:2 patterns) of maize (cv. PAN 6479) with mucuna (Mucuna pruriens) or sunnhemp (Crotalaria juncea) on maize productivity and summer cover crop biomass production. In a separate experiment effects of relay intercropping sunnhemp, mucuna and sorghum (Sorghum bicolor) on biomass accumulation and maize productivity were investigated. Decomposition, N and P release from both winter cover crops and summer cover crops were also assessed in laboratory incubation experiments. Oats, grazing vetch and forage peas cover crops produced mean dry mass of 13873 kg/ha, 8945.5 kg/ha and 11073 kg/ha, respectively, while lupin had the lowest dry mass of 1226 kg/ha over the two seasons. Oats responded to fertilization while, there was little or no response from the other winter cover crops. Oats and grazing vetch also reduced weed density by 90 % and 80 % respectively while lupin only reduced weed density by 23 % in relation to the control plots. Nitrogen uptake was 254 kg N/ha for oats while it was 346 kg N /ha for grazing vetch. In the subsequent summer season, grazing vetch and forage pea residues significantly (P < 0.01) improved soil inorganic N. Oat and grazing vetch residues significantly (P < 0.05) reduced weed dry masss and weed species diversity compared to plots with lupin residues and the control. Lack of maize fertilization tended to reduce maize yields but not for maize grown on grazing vetch residues. From an economic perspective, grazing vetch resulted in the highest returns. Decomposition of winter cover crops was much faster for grazing vetch followed by forage peas and lastly oats. Oats had 40 % ash free dry mass remaining after 124 days while grazing vetch and forage peas had 7 % and 16 % respectively. Maximum net mineralized N and P were greater for grazing vetch (84.8 mg N/kg; 3.6 mg P/kg) compared to forage peas (66.3 mg N/kg; 2.7 mg P/ha) and oats (13.7 mg N/kg; 2.8 mg P/kg). In the strip intercropping trials, sunnhemp achieved the highest biomass yield of 4576 kg/ha in the 3:2 pattern while mucuna achieved 1897 kg/ha for the same strip pattern. The 3:2 strip intercropping pattern slightly depressed yields, however, yield reduction was more pronounced in the first season where water stress was experienced. Growing maize on previous cover crop strips failed to increase maize productivity probably due to weed growth during the fallow reducing mineral N in these strips. Decomposition was faster in sunnhemp leaves and mucuna compared to sunnhemp stems. Sunnhemp stems had about 65 % of ash free dry mass remaining after the end of the experiment at 132 days while just over 10 % of mucuna and sunnhemp leaves still remained. Mucuna mineralized 60 mg N/kg and 3.2 mg P/kg and sunnhemp mineralized 45 mg N/kg and 3.5 mg P/kg. Relay intercropping did not significantly (P > 0.05) affect maize biomass and grain yield. Sorghum experienced the largest drop in biomass when relay-intercropped with maize. Mucuna resulted in the highest N uptake (271 kg N/ha) in sole cropping while sorghum had the lowest (88 kg N/ha). Grazing vetch results in high biomass yields with minimal fertilizer application in a warm-temperate climate. Grazing vetch mulch is also the most cost effective mulch for better early weed control, improving soil mineral N status, water conservation and ultimately enhanced maize productivity in smallholder irrigation maize-based systems. The 3:2 pattern maximizes summer cover crop biomass yields compared to the 6:2 and 4:2 patterns. However, the 3:2 pattern may slightly depress yields in a water stressed environment. Relay intercropping mucuna, sunnhemp and sorghum into a maize crop at 42 days after maize sowing has no effect on maize productivity while cover crop biomass yields are low. Having a long winter fallow period after maize harvesting, a common practice in the study area, reduces the positive impact of legume cover crops on soil mineral N. Results suggest that winter cover crops may result in weed control, soil fertility and maize yield improvement benefits while a long fallow period may cancel-out these benefits for summer cover crops. Grazing vetch is a cost effective cover crop that produces high maize yields with minimal fertilizer input. Maize growing on oat mulch requires more fertilizer application than crops growing on grazing vetch mulch. Conservation agriculture systems in which summer cover crops are grown alongside the maize crop with a long winter fallow period do not produce the intended CA benefits.

Drip irrigation lines placed 15 cm (deep) and 5 cm (shallow) below soil surface were compared to furrow irrigation with zucchini squash as a summer crop and cabbage as a winter crop. Both crops were grown on the same drip lines in each treatment. Urea phosphate was injected in drip lines during growing season while the furrow-irrigated plots received preplant application of phosphorus. In squash, deep lines produced higher yields than did shallow. Deep-drip yields were comparable to those with furrow but used half the water and half the fertilizer. In cabbage, deep-drip yielded slightly higher than shallow-drip and furrow. In these studies, deep-drip was superior in applying water and fertilizer.

Irrigation termination trials were continued in 1988 to evaluate a newer, popular upland variety and pima S-6. Irrigation in the first week of September increased the yield of a May planting of DP 77, but not of two trials in 1988 with early April planting dates. A March planting of pima S-6 failed to respond to a 10 September irrigation on Coolidge sandy loam.

A single field study was conducted in 1997 at the Maricopa Agricultural Center (1,175ft. elevation) to evaluate the effects of three dates of irrigation termination on the yield of a common Upland cotton variety (DP NuCOTN 33b). Planting date was 9 April (668 HU /Jan 1 86/55° F thresholds. Three dates of irrigation termination (IT1, IT2, and IT3) were imposed based upon crop development into cut -out. The earliest irrigation termination date, IT1 (7 August) was made as early as possible in an attempt to provide sufficient soil - water such that bolls set at the end of the first fruiting cycle would not be water stressed and could be fully matured. The second termination (IT2) date was 20 August, and provided one additional irrigation over IT1. The final (IT3) date was 17 September, which was staged so that soil moisture would be sufficient for development of bolls set up through the last week of September and provide full top-crop potential. Lint yield results revealed no differences among any of the IT treatments. Mirconaire values increased slightly with later IT dates.

Irrigation scheduling, by keeping track of irrigation applications, soil storage and crop water use, has been computerized by a number of different individuals. A key component of the computerized methods is the estimation of a reference crop evapotranspiration rate. Complaints about one such method, AZSCHED, led the authors to compare the reference crop evapotranspiration values calculated by AZSCHED with those calculated by a second procedure available used by AZMET. Results of the comparison indicated that no significant difference existed between methods, for either a traditionally "long season", or a contemporary "short season" growing period. AZSCHED did estimate crop water use to be about 5% - 8% more than AZMET, an amount that is not of importance considering the irrigation inefficiencies created by field non-uniformities. Experience by the authors indicates that inappropriate selection of irrigation efficiencies and/or soil water holding capacity may be the main cause of user complaints.

Field experiments were initiated at sites in Marana, Coolidge and Goodyear, Arizona, in the Fall of 2001, in a cotton-based, conservation tillage project. In the 2002 cotton season, following cover and grain crops, soil and water management assessments were made to evaluate the impact of conservation tillage on surface irrigation performance. An additional site was added in the winter of 2002 at Maricopa, Arizona. Analyses included soil texture, infiltration rate and water advancement. At Coolidge, the Conservation plots had higher infiltration rates and longer advance times than the Conventional plots in 2002, 2003 and 2004. At Marana, infiltration rates were initially higher for the Conservation plots but the rates converged at the end of four hours in 2002. In 2003, the Conventional plots infiltrated about one inch more and the opposite occurred in 2004, where the Conservation plots infiltrated about 1 inch more than the Conventional. The advance times for Marana showed the water in the Conventional wheel rows to be the fastest. At Goodyear, the Conservation plots infiltrated more than the Conventional plots in 2002. This also resulted in a slower advance time for the Conservation plots. In 2003, due to tillage by the grower, treatment effects could not be compared and the site was abandoned in 2004. At Maricopa, the Conservation plots infiltrated almost 2.2 inches more water than the Conventional plots and the water reached the end of the field three hours ahead of the fastest Conservation plot in 2003. In 2004, the Conservation plot infiltrated just over 1½ inches more water than the Conventional plots with the Conventional plots having faster advance times. Seasonal irrigation water applications to each treatment were relatively equal for all the sites with the exception of Coolidge. Here, the long field combined with sandy soil made it difficult to adequately irrigate the Conservation plots. In 2002, an additional 21 inches of water was applied to the Conservation plots. In 2003, that amount was reduced to 12.5 inches. The 2004 irrigation data are not yet available. The yield data show a significant difference between years and different sites. In 2002, only the yields measured at Coolidge were significantly different with the Conservation yielding higher than the Conventional. This may have been due to the increase water application. In 2003, the opposite occurred and the Conventional plots yielded more than the Conservation plots. This may have been due to herbicide damage. At Maricopa the Conventional plot also yielded more than the Conservation plot in 2003 but there was no measured difference in 2004. The Marana site had equal yields for both treatments except for the final year, 2004, when the Conventional yielded higher than the Conservation treatment. Indications are that conservation tillage does impact irrigation performance and it may not be suitable for all locations depending on soil type and field layout.

Field experiments were conducted in 2004 and 2005 at the University of Arizona Maricopa Agricultural Center (1,175ft. elevation) to evaluate the effects of five irrigation termination (IT1, IT2, IT3, IT4, and IT5) dates on yield and fiber micronaire of eleven Upland cotton varieties and one Pima variety. In addition, the economic relationships of IT treatments were also evaluated. The experimental design was a split plot in a randomized complete block design with three replications. The main treatments included the five IT dates and the subunits consisted of 11 Upland varieties and a Pima variety. The first two IT treatments (IT1 and IT2) were imposed with the intention of terminating irrigations very early and pre-maturely at peak bloom. Based upon current UA recommendations for IT to complete a single cycle fruit set, the more optimal date of IT would have included one or two additional irrigations (beyond IT1 and IT2). In this experiment, IT2 was structured to provide an additional (one) irrigation just past peak bloom. For the IT3 plots, the intention was to attempt to time termination in advance of cutout. The 2004 and 2005 IT4 and IT5 were imposed to attempt to complete the primary fruiting cycle development and produce a second cycle fruit set that require irrigations until late August and late September, respectively. In general, lint yield and micronaire results revealed significant differences among the IT treatments and varieties. In a similar fashion to a previous set of IT experiments (2000-2002), lint yield and micronaire values consistently increased with later IT dates. The best combined lint yield and micronaire results were achieved with IT4 date, which received 12 and 18 in. less irrigation water than IT5 in 2004 and 2005, respectively. In 2004 and 2005, the 12 and 18 in. water saved equate to approximately 20% and 30% less water used under the conventional practice, respectively. The average marginal value of water for all eleven Upland varieties in going from IT1 to IT2, IT2 to IT3, IT3 to IT4, and IT4 to IT5 for November 2004 prices and low carrying costs is calculated at $320.07, $150.15, $100.54, and -$28.16 per acre-foot of water. If steeper mike discounts (November 1999), a lower base lint price (45¢/lb.), and higher costs (i.e., more costly insecticide and chemical costs) are imputed to extend the crop, the marginal value of an acre-foot of water for all Upland varieties and replications in going from IT1 to IT2, IT2 to IT3, IT3 to IT4, and IT4 to IT5 is estimated at $164.04, $48.15, $12.97, and -$94.79. Profitability and the value of water for extending the season varies quite markedly between different varieties and termination dates.

[Abstract]: Sugarcane farmers in Bundaberg have had limited access to irrigation water over the last ten years. The district has the potential of growing 3.8 million tonnes of sugarcane. However, a series of dry seasons saw this reduce to 2.1 million tonnes in 2002. Compounding the effects of both dry seasons and limited water supplies has been a 30% reduction in the sugar price over this period. The irrigation requirement of sugarcane in the Bundaberg area is 8 ML/ha. The original allocated volume for sugarcane production in this area was 4.5 ML/ha (based on 1970 production areas). However, as the area under production has increased and announced allocations in each year has reduced, this allocation is now equivalent to an application volume of about 2 ML/ha A change from the traditional practice of full irrigation is required as water supplies become depleted. As there were no clear guidelines on how growers could respond to diminishing water supplies, this research investigated opportunities to fine tune irrigation practices and the performance of irrigation systems (ie. low cost solutions) that would assist growers to maximise sugarcane yield. A grower survey was initially conducted to identify current practice and opportunities for change. Field investigations focused on the performance of water winch and furrow irrigation systems, which make up 91% of the irrigated area in the district. As most of these application systems have insufficient capacity to meet crop demands opportunities to schedule irrigations were limited to start up after rain. Improvements in irrigation system performance were found to provide the greatest potential to increase sugarcane yield under conditions of limited water. Investigations identified that irrigation performance could be significantly improved through relatively minor adjustment. Field trials found that wind speed and direction significantly influenced the performance of travelling gun irrigators. Although growers were generally aware of the effects of wind, meteorological data suggested that the opportunity to operate water winches in low wind conditions is limited. Changing to a taper nozzle under moderate to high wind conditions will reduce the effect of wind on performance. This practice was found to improve the uniformity (measured by Christiansen’s Uniformity Coefficient, CU) by 16%. The grower survey indicated that there was no preference towards the use of taper nozzles in windy conditions. Additional trial work developed a relationship between the variation in water applied to the field through non uniformity and sugarcane yield. An 8% reduction in yield was determined for a 10% reduction in CU. This indicated that changing to a taper nozzle could potentially increase sugarcane yield by 15% in high wind conditions. Other settings, which also influenced uniformity, included lane spacing and gun arc angle Simple changes to the operation of furrow irrigation systems were also found to dramatically improve irrigation performance. Field measurements in combination with simulation modelling of irrigation events using SIRMOD II identified that current irrigation performance ranged in application efficiency from 45 to 99% (mean of 79%) and a distribution uniformity from 71 to 93% (mean of 82%). Both application efficiency and distribution uniformity were increased to greater than 90% and 84% respectively, except on a cracking clay soil. Improvements in application efficiency and distribution uniformity were achieved by adjusting furrow flow rate (cup size), turning the irrigation off at the right time (ie. just as it reached the end of the field) and banking the end of the field. Growers had a good understanding of the correct cut off time and were attentive to reducing run off through either banking ends or tail water return. However, growers had a poor understanding of the significance of furrow flow rate. Other opportunities to improve irrigation performance on high infiltration soils included alternate furrow irrigation and shallow cultivation practices which maintained compaction in the interspace and reduced infiltration. Soil moisture and crop growth measurements indicated that sugarcane yield could be maximised by starting the irrigation rotation earlier after rainfall (ie. at a deficit equal to the irrigation amount). These observations were modelled using the crop simulation model APSIM sugar to assess the strategy over a longer time interval and the influence of seasonal variation. Simulation modelling showed that final sugarcane yields were not sensitive to irrigation start-up strategies. Yields for the start-up strategies modelled varied by less than 5 tc/ha. This minor difference occurred as the crop yield was driven by the total amount of water available to the plant. The limited amount of irrigation water available to the plant (2 to 3 ML/ha) had only a minor effect on the water balance and no significant change to effective rainfall between strategies. The greatest difference in yield occurred between irrigation treatments when water was left over at the end of the season (9.2 tc/ha). Starting irrigation earlier after rainfall events (on a 14 day rotation) provided the greatest opportunity to use all of the available irrigation supply. By comparison, delaying the application of the first irrigation after rainfall resulted in some of the irrigation water not being applied in 30% of years.

Optimum design and management of irrigated wheat production is limited by the scarcity of information available on yield variability. The purpose of this study was to evaluate the spatial variability in soil-water parameters and the effects compared to grain yield response under level-basin irrigation. Three levels of seasonal irrigation water and two border lengths were used. Grain yields were found to increase significantly with the amount of water applied and soil water depletion (estimate of crop evapotranspiration), although yield variability was greater with reduced or deficit irrigations. Variations in soil water content were responsible for about 22% of the variability in grain yield, indicating that other soil and crop- related factors had a significant influence on production. Spatial dependence was exhibited over a greater distance at the wetter compared with the drier irrigation regimes.