Dissertations / Theses on the topic 'Agronomy'

<p> There are an insufficient number of university students, specifically women, graduating with an education in agronomy to fill work force demands. This need, driven partially by population growth, is increasing due to growing rates of industrialization and consequential environmental issues. Agronomy pays special attention to the supply and demand of resources from the environment. Though there is an apparent regression in students choosing an education in agronomy, there is a need for their skill set. This study hypothesized that urban and rural women have different perceptions that influence them towards agronomy careers. To quantify these perceptions, a survey was issued to women at the 2014 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America Joint Annual Meetings in Long Beach, CA, USA. Rural and urban women had significantly different (p &lt; 0.05) perceptions about their birthplace environment's influence on career choice, proving the hypothesis. Rural women were more influenced by this setting than their urban counterparts, which could prove to be a major issue if urban encroachment progresses. This study defines the rural urban birthplace population break at 25,000 for women in agronomy careers. This population break knowledge should be helpful for revisions of marketing, recruitment, and retainment programs. Other trends presented are helpful because together they disclose potential future investigations into agronomy women's perceptions, their decision-making processes, and what influences their career choice.</p>

Extensive coastal sabkhas in the northern Gulf of California in North America are colonized by Distichlis palmeri, an endemic perennial grass that produces a grain that was harvested as a staple food by native Cocopah people. Previous short-term trials have shown good vegetative growth but low grain yields. During outdoor trials under anaerobic saline soil conditions of paddy-style irrigation, D. palmeri exhibited high salt tolerance, grain and biomass production. Reproductive maturity was reached four years after initial establishment of plants from seed and a 1:3 mixture of male and female plants produced 231-310 g m⁻² of grain, with nutritional content similar to domesticated grains, confirming the feasibility of developing D. palmeri as a perennial grain and biomass crop for salinized soils and water supplies. Salicornia bigelovii Torr., a cosmopolitan annual coastal marsh succulent, produces seed with high oil content and has been suggested as a potential cash crop for fuel production from saline irrigation but its domestication and development into a cost effective commodity has been slow. A breeding and selection program for agronomic traits that will provide multiple landscape and ecosystem services that could enhance cost benefits of the agronomy of S. bigelovii was initiated during a two year period while producing seed for a pilot system at the Masdar Institute in Abu Dhabi, U.A.E. A concept for a saline landscape designed to consume and concentrate saline waste streams was developed and demonstrates the feasibility and potential to support agronomy of halophytes within a built landscape ecology akin to coastal marsh systems. Exploration and development of potential services halophytes could provide and field testing of selected halophytes for their potential to produce food, fuel, fiber and habitat under designed and managed domestication in our salinized soils with saline waste irrigation needs our continued investigation.

L'augmentation de la complexité des systèmes agricoles nécessite des outils d'aide à la prise de décision sophistiqués capables de gérer plusieurs critères et d'accommoder des tâches complexes d'analyse des compromis. Cette thèse développe des visualisations qui facilitent les processus de prise de décision en agronomie, avec trois contributions principales : (i) comprendre comment la provenance peut soutenir l'analyse des compromis, (ii) articuler des besoins de conception et de visualisation pour soutenir la comparaison de groupes dans des scénarios de compromis, et enfin (iii) comprendre comment différentes visualisations peuvent affecter les comparaisons et la prise de décision dans l'analyse des compromis. Après un chapitre d'introduction et un chapitre sur les travaux connexes, la thèse détaille ces trois contributions.Le 3ème chapitre examine comment les mécanismes de provenance analytique peuvent aider les experts à se souvenir et à suivre des analyses de compromis complexes. Nous avons développé VisProm, un outil web intégrant des vues de provenance dans les visualisations pour aider les experts à suivre les compromis et leurs objectifs lors de l'exploration de résultats de simulation complexes. Des sessions d'observation avec des experts ont révélé huit tâches clés soutenues par nos conceptions, mettant en lumière de nouvelles opportunités pour l'analyse des compromis guidée par la provenance, telles que le suivi de la couverture de l'espace de compromis et l'exploration de scénarios alternatifs. Un résultat clé a été la nécessité de considérer les objectifs conflictuels et de comparer comment différentes solutions ou espaces de compromis se comportent face à ces objectifs.Le 4ème chapitre explore les besoins et les défis auxquels sont confrontés les experts lorsqu'ils comparent des espaces de compromis (souvent exprimés sous forme de groupes de points de données, par exemple, des groupes de résultats de simulation) qui optimisent différents objectifs. À travers des ateliers avec des experts du domaine et des concepteurs de visualisations, nous avons identifié des besoins de conception et de visualisation pour soutenir la comparaison de groupes dans des scénarios de compromis. Ce chapitre met les bases pour développer des techniques de visualisation capables de comparer des groupes représentant différents compromis en fonction des objectifs qu'ils optimisent. Cela a mené à la mise en œuvre d'un prototype de visualisation qui encode visuellement diverses métriques de compromis, en communiquant les priorités des experts, la notion de solutions idéales, et la distance des groupes de solutions par rapport à ces idéaux.Le 5ème chapitre se concentre sur l'évaluation des techniques de visualisation pour comparer des groupes de points (solutions) lorsqu'ils représentent différents compromis. S'inspirant des besoins identifiés dans le chapitre précédent, nous avons sélectionné trois techniques prometteuses de visualisation pour les étudier. Ces techniques encodent visuellement les priorités des compromis et les solutions idéales de différentes manières, soit en couplant, soit en découplant les métriques de compromis. Nous avons mené une étude utilisateur pour comprendre comment ces visualisations influencent les décisions de comparaison et la qualité des explications de ces décisions. Les résultats montrent que les techniques qui séparent visuellement l'encodage des priorités et des solutions idéales entraînent une charge cognitive plus élevée et une confiance auto-évaluée plus faible, mais soutiennent des stratégies de décision plus variées par rapport aux visualisations intégrées. Elles étaient cependant toujours préférées par rapport à la visualisation de référence.La thèse conclut avec des discussions et des perspectives sur les directions futures issues de ce travail<br>The increasing complexity of agricultural systems necessitates sophisticated decision-making tools that can handle multiple criteria and accommodate complex trade-off analysis tasks. This thesis develops visualizations that facilitate decision-making processes in agronomy. This work has three main contributions: (i) understanding how provenance can support trade-off analysis, (ii) articulating high-level design and visualization needs to support group comparison in trade-off scenarios, and (iii) understanding how different visualizations can affect comparisons and decision-making in trade-off analysis. After an introductory chapter and a chapter on related work, the thesis details these three main contributions.The 3rd chapter of the thesis investigates how analytic provenance mechanisms can assist experts in recalling and tracking complex trade-off analyses. We developed VisProm, a web-based system integrating in-visualization provenance views to help experts track trade-offs and their objectives when exploring complex simulation results. Observation sessions with groups of experts revealed eight key tasks supported by our designs, highlighting new opportunities for provenance-driven trade-off analysis, such as monitoring trade-off space coverage and tracking alternative scenarios. One key outcome was the need to consider conflicting objectives and compare how different solutions or trade-off spaces fare under these objectives.Building on this, the 4th chapter explores the needs and challenges experts face when comparing trade-off spaces (that are often expressed as groups of data points, e.g., groups of simulation results) that optimize different objectives. Through workshops with domain experts and visualization designers, we identified high-level design and visualization needs to support group comparison in trade-off scenarios. This chapter lays the groundwork for developing effective visualization techniques for comparing groups that represent different trade-offs in terms of what objectives they optimize. They led to the implementation of a visualization prototype that visually encodes a variety of trade-off metrics. These encode and visually communicate experts' priorities in terms of objectives, the notion of ideal solutions, and how far current groups of solutions are from those ideals.The 5th chapter focuses on the evaluation of visualization techniques for comparing groups of points (solutions) when they represent different trade-offs. Motivated by the visualization needs and design requirements of the previous chapter, we selected three promising tabular-based visualization techniques to study. These techniques encode trade-off priorities and ideal solutions in different ways: coupling or decoupling the trade-off metrics and presenting them visually. We conducted a user study to understand how visualizations affected comparison decisions and quality of decision explanations. The findings from this study highlight that techniques that visually separate the encoding of priorities and ideal solutions lead to higher mental load and lower self-reported trust but may support more varied decision strategies than integrated visualizations. But they were always preferred over a baseline visualization.We conclude the thesis with a list of discussions and perspectives for future directions stemming from the results of this work

Field peas have been under evaluation in the northern cropping region of Australia for the past five years and have been shown to offer growers advantages in terms of soil fertility, weed control and a disease break for following winter cereal crops. The advanced lines identified with attributes suitable for reliable production of the crop in the region have all been semileafless types, and of either semi dwarf or tall plant height. Before the crop can be successfully delivered to the regional growers, information on planting time, planting rate and the effect of the crop on soil moisture availability for subsequent crops is needed. In this way, growers can evaluate if peas will fit into their farming system. The work reported in this thesis addresses the issues of row spacing and plant density as they determine planting rate as well as the effect of growing peas on soil moisture content during the growing season. This was done using six field pea genotypes varying for leaf type and plant height grown for three years in a three replicate randomised complete block design experiment, split for row spacing and plant density. Choice of row spacings were 13, 25 and 50 cm, while plant density treatments were 15, 30, 60 and 120 plants/m2

Master of Science<br>Department of Agronomy<br>Dorivar Ruiz Diaz<br>Two studies were conducted to evaluate phosphorus response. The first study focused on genetic improvements in corn (Zea mays) for water limited scenarios on phosphorus uptake. The object of the first study was to evaluate plant response to fertilizer and soil phosphorus for contrasting corn hybrids, including a drought tolerant (DT) and conventional hybrid. This study was established at seven locations for two years (2011 and 2012). Four locations were rain fed and three locations were under irrigation. Fertilizer treatments included phosphorus fertilizer at various rates and placements for the two different hybrids. The experimental design randomized complete block with factorial arrangement in four replications. Early growth biomass, early season whole plant tissue concentration (V6), ear leaf tissue concentration, and grain yield was measured throughout the season. Results showed differences in all measurements between hybrids. Differences in most measurements were also significant with fertilizer application. The DT hybrid had less early growth and P uptake but had higher ear leaf P concentration as well as higher yields. The second study focused on P placement, P stratification may be a concern for producers using reduced tillage systems. The objective of this study was to evaluate different placements and rates of P fertilizers in two crops, corn and soybean (Glycine max). This study is currently ongoing; however, here we are presenting data from three locations and four years (2009-2012). Two of the locations were rain fed and one was irrigated. There were four different fertilizer rates with three different placements as well as various combinations of those placements. The experimental design was randomized complete block with four replications at two locations and three replications at one location. Corn early growth biomass, whole plant tissue concentration, ear leaf tissue concentration, soybean uppermost fully open trifoliate P concentration, and yield for both crops were evaluated throughout the season. Results showed response to the phosphorus treatments in all the measured parameters. Results also showed differences in all measured parameters except yield, were significantly affected by placement.

The Triticeae tribe DUMORTER in the grass family (Poaceae) includes the most important cereal crops such as wheat, barley, and rye. They are also economically important forage grasses. Elymus is the largest and most complex genus with approximately 150 species occurring worldwide. Asia is an important centre for the origin and diversity of perennial species in the Triticeae tribe, and more than half of the Elymus are known to occur in the Asia. Cytologically, Elymus species have a genomic formula of StH, StP, StY, StStY, StHY, StPY, and StWY. About 40% of Elymus species are still unknown for the genomic constitution and some have questionable genomic combination. However, the origin of the Y genome is unknown. In order to identify the origin of the Y genome, 212 accessions of Elymus, Pseudoroegneria, and Hordeum species were tested using a Y genome specific Sequence Tagged Site (STS) marker. We obtained evidence supporting the hypothesis that the Y genome in some Elymus species shared a progenitor genome with the St genome. Our study suggested that Pseudoroegneria spicata (PI 232134), P. ferganensis (T 219), and P. libanotica (PI401326) are the donors of the Y genome in the Elymus species. The DNA sequences of the Y-genome marker in these three Pseudoroegneria species are more similar to those obtained from Elymus species having the Y genome than those from Hordeum marinum and H. murinum, making the Xa and Xu genomes less likely the donors of Y genome.

France ginseng est une jeune entreprise qui cultive un ginseng "Made in France" de façon pérenne et rentable en France. Cette entreprise a développé un concept innovant de production de plante médicinale. En vue d'accélérer son développement et d'optimiser ses connaissances et ses techniques, un ambitieux programme de recherche et développement est lancé. Les objectifs du projet proposé porteront sur l'identification de facteurs agronomiques favorisant l'accumulation des ginsénosides et la qualité du produit obtenu. Plus précisément, il s'agira de définir et justifier via la physiologie de la feuille et de la racine, les conditions permettant d'obtenir ces meilleures teneurs et compositions en ginsénosides. A cette fin, des essais en conditions de cultures sous ombrières sur 2 sites de production ou en conditions contrôlées seront mis en place et conduits sur des plants de 1 à 4 ans. Divers traitements post-récolte seront associés à ces essais de production<br>France ginseng is a young company that cultivates ginseng "Made in France" in a sustainable and profitable way in France. This company has developed an innovative concept of medicinal plant production. In order to accelerate its development and to optimize its knowledge and techniques, an ambitious program of research and development is launched. The objectives of the proposed project will focus on the identification of agronomic factors improving the accumulation of ginsenosides and the quality of the product obtained. More precisely, the aim is to define and justify via the physiology of the leaf and the root, the conditions allowing to obtain the best contents and compositions in ginsenosides. For this purpose, tests under shade-culture conditions on 2 production sites in field or in controlled conditions in a greenhouse will be set up and conducted on plants of 1 to 4 years. Various post-harvest treatments will be associated with these production trials

Dislodgeable foliar residues (DFR) can be a primary route for human exposure following pesticide application to turfgrass areas. Consequently, a significant portion of applied pesticide may be available for human exposure via dislodgeable residues. In this study, DFR were determined over a 15-day-period following application of the broadleaf weed herbicide carfentrazone (Ethyl alpha, 2-Dichloro-3-{2-chloro-4-fluoro-5-{4-(difluoromethyl)-4, 5-dihydro-3-methyl-5-oxo-1H-1, 2, 4-triazol-1-yl}-4-fluorobenzenepropanoate ), the pre-emergent herbicide prodiamine (5-dipropylamino-α,α,α-trifluoro-4,6-dinitro-o-toluidine or 2,6-dinitro-N1,N1-dipropyl-4-trifluoromethyl-m-phenylenediamine ) and the insecticide bifenthrin (2-methylbiphenyl-3-ylmethyl (1RS,3RS)-3-[(Z)-2-chloro-3,3,3-trifluoroprop-1-enyl]-2,2-di-methylcyclopropanecarboxylate) to a mature stand of ?Confederate? Tall Fescue (Festuca arundinacea Schreb). Dislodgeable foliar residues were determined by wiping treated turfgrass with a distilled-water-dampened cheesecloth and analyzing samples using gas chromatography/ mass spectrometry (GC/MS). Less than 20% of the total applied carfentrazone was dislodged with 14% of DFR occurring immediately after application and a total of 6% for the remainder of the 15-day study. Prodiamine DFR averaged 80% over the 11-day study with dislodgeable residue levels ranging from a maximum of 17% of the total applied chemical 8 hours after treatment to a low of 4% 11 days after treatment. Approximately 35% of the total applied bifenthrin was available to be dislodged over 15-day study with 34% DFR loss occurring immediately after application and a total of 1% for the remainder of the sampling periods. If pesticides are allowed to dry on the leaf surface, shortly after application carfentrazone, prodiamine and bifenthrin pose minimal risk to human health via dermal exposure when applied at the labeled rate.

<p> The Mississippi River Valley Alluvial Aquifer (MRVAA) aquifer is the principal water source for Mid-South irrigators, but the current rate of withdrawal from the aquifer is not sustainable. Means to increase the sustainability of the MRVAA is to improve corn&rsquo;s water use efficiency (WUE) while, concurrently, maintaining or improving profitability. The objectives of this experiment were to determine the effects of sensor-based irrigation threshold, planting date, and hybrid on corn grain yield, WUE, and net returns above seed and irrigation cost. Season long irrigation thresholds of -50 kPa full irrigation (FI) and -125 kPa limited irrigation (LI) were used, utilizing furrow irrigation. In conclusion, utilizing a delayed irrigation trigger of -125 kPa decreases grain yield and, ultimately, net returns in years with less naturally occurring rainfall, but increases WUE. Shifting the planting date earlier and using full-season (FS) hybrids, increases grain yield, WUE, and net returns.</p><p>

<p> Weeds are one of the biggest challenges for organic growers because of the alternative weed control methods. Air-propelled abrasive grit management has been reported to control weed seedlings in corn and soybeans while maintaining yield. This research examined the weed control, corn and soybean yields, nitrogen mineralization, and nitrogen yield responses from grits. The grits used in this research included: Phytaboost Plant Food 7-1-2 (soybean meal), Sustane 8-2-4 and 4-6-4 (turkey litters), and two non-fertilizer grits: Agra Grit (walnut shells) and corn cob meal. Field studies were conducted from 2015 to 2017 in Aurora, SD, Beresford, SD and Morris, MN. Nitrogen mineralization and total nitrogen release from selected grits in two different soils were evaluated in 100 d incubations. The response of corn, wheat, red russian kale and velvetleaf to Sustane 8-2-4, Agra Grit and corn cob meal amended soil was investigated. Agra Grit consistently reduced in-row broadleaf weed biomass in all four site years, whereas when grass weeds were dominant, in-row weed biomass was not reduced with two grit applications. When grit treatments reduced in-row weed density, corn yield increased with fertilizer grits higher than the weed-free check. In-row weed biomass in soybeans was similar among treatments, but when total weed biomass was reduced, the soybean yields were 31 to 55% greater in the grit treatments than weedy checks. Organic fertilizer grits increased soil available nitrogen with 50 to 70% of nitrogen mineralized. Non-fertilizer grits immobilized soil available nitrogen. Plant height and dry weight of wheat, red russian kale, and velvetleaf were greater when the soil was amended with Sustane 8-2-4 compared with Agra Grit, corn cob meal, and no-grit control, although fresh weights and relative greenness were similar among treatments. The use of organic fertilizer grits provide a source for nitrogen for all plants in the targeted area, whereas non-fertilizer grits may immobilize nitrogen. Corn and soybean yields can be increased when two applications of air-propelled grits reduce weed density, regardless the type. Grits may provide nitrogen for the crop but weed control is critical as additional nitrogen also may stimulate weed growth.</p><p>

<p> Row patterns affected irrigated corn productivity when grown in the Mid-South region of the United States. Narrow (76 cm) row spacing increased grain yield 8% when compared to traditional wide (96-102 cm) row spacing. Twin rows (20-25 cm spacing) in a wide (96-102 cm) row pattern, produced similar grain yield as a traditional wide single row. At a normal plant density of 79,040 ha^-1, traditional wide rows yielded 10.51 Mg ha^-1, twin wide rows yielded 10.34 Mg ha^-1, and the narrow rows yielded 11.33 Mg ha^-1. Growing corn at various plant densities did not affect corn grain yield response to various row patterns. As a comparison the traditional wide rows and twin rows were similar in their yield, and the narrow rows performed better. Corn grain yields for the traditional 96-102 cm wide single rows were 11.20 Mg ha^-1, wide 96-102 cm twin rows yielded 11.22 Mg ha^-1, and narrow 76 cm rows produced 12.07 Mg ha^-1. Row pattern had no effect on corn plant height, photosynthetically active radiation (PAR), leaf area index (LAI), SPAD, stalk diameter, and plant lodging in either study.</p><p>

Thesis (MScAgric)--Stellenbosch University, 2011.<br>ENGLISH ABSTRACT: Glyphosate remains an important herbicide in weed control. This is due to several positive attributes it has including sytemicity, wide spectrum of weed control and environmental friendliness. Its efficacy and lack of residual activity are therefore important to ensure adequate weed control without imposing hazards to the environment. Despite these favourable attributes for weed control glyphosate has its shortcomings. Evolution of resistance to glyphosate has been a major concern from 1996. However, there are other factors that reduce the maximum potential of glyphosate. Any factors that reduce glyphosate efficacy may result in the target plant being subjected to non-lethal concentrations of glyphosate. This in turn may predispose the plants to developing herbicide resistance. Some factors that may influence efficacy of glyphosate, and therefore be possibly selecting for resistance were investigated in this study. Although glyphosate is a postemergence herbicide, its efficacy is not exempt from the effect of soil and nutrients in which the weeds occur. The possibility of this occurring was investigated in a greenhouse study on ryegrass (Lolium spp.) In this study ryegrass was grown in three soils: pure sand (SS), soil from pasture paddock (PS) and soil from crop field (CS). The soils varied in nutrient composition and, although all were classified as sand, they had varying proportions of sand, loam and clay. This investigation consisted of four experiments. The first experiment was investigating the effect of growing a susceptible commercial ryegrass cultivar on PS, CS and SS soils on the efficacy of glyphosate (360 g a.i. L-1 formulation) applied at five glyphosate application rates (GAR). The GARs were 0 (0x), 67.5 (1/8x), 135 (1/4x), 270 (1/2x) and 540 (1x) g a.i. ha-1. The second experiment investigated the effect of growing a susceptible commercial ryegrass cultivar and a glyphosate resistant ryegrass biotype on PS and CS soils on the efficacy of glyphosate. The application rates were 0 (0x), 270 (1/2x), 540 (1x), 1080 (2x) and 2160 (4x) g a.i. ha-1. The third and the fourth experiments were similar to the first experiment except: The latter investigated the role of nutrient content of irrigation water (pure water or balanced nutrient solution) and; the former investigated the effect of soil activity (by covering the soil surface with cotton at the time of spraying) of glyphosate with regard to the role it plays on efficacy of glyphosate. Our findings showed that: i) soil affects the efficacy of glyphosate with more control (19% survivors) found in the PS soil compared to 50% and 62% survivors in CS and SS soils respectively, this effect may be dependent upon the species resistance as; ii) the effect in the resistant ryegrass biotype was reversed with about 95% of survivors in the PS soil compared to about 78% in CS soil; iii) efficacy of glyphosate is influenced by the soil nutrient status and the nutrient content of the irrigation water. This was shown by decrease in the control of ryegrass (100% survivors) grown in SS soil when fed with pure water compared to 45% when nutrient fed. In PS soil there was no significant effect. This was probably due to inherently higher nutrient content of the PS soil; and iv) glyphosate efficacy is influenced by the amount of glyphosate reaching the soil (absorbed through the roots). This was shown in PS soil where 1/8x GAR resulted in 93.3% survivors in covered soil compared to 60% in uncovered soil. A similar trend was also observed at 1/4x GAR. An opposite effect was shown in SS soil with 0% and 40% survival at 1/4x GAR in the covered and uncovered soil respectively. Glyphosate has been hailed as an environmentally friendly herbicide as it rapidly degrades in soil and it sorbs on metals embedded in soil matrix. However, reports in the literature have showed reduction in crop yield due to soil glyphosate residues. In these studies, glyphosate phytotoxicity was found to be dependent on certain soil characteristics and nutrient content. Following this, a greenhouse study was conducted to assess the phytotoxic activity of glyphosate on a susceptible commercial ryegrass cultivar grown in PS, CS and SS soils. Glyphosate was applied at 0 (G1), 540 (G2) and 3240 (G3) g a.i. ha-1. Ryegrass seedlings of comparable size were transplanted into the soil at intervals of two hours, three weeks and four weeks after glyphosate application referred to as TAS1, TAS2 and TAS3 respectively. Evidence of soil glyphosate activity was shown by the decrease in percentage survival with the application of glyphosate. This was significant in the SS soil where about 60% and 48% survival in G1 and G2 GAR respectively was observed compared to about 100% in the untreated control when transplanted three weeks after glyphosate application. The decrease in percentage survival was time mediated with significant effect of G2 GAR shown at TAS 1 whereas at G3 GAR the effect was significant at TAS1 and TAS 2. At TAS 3 there was no effect at all GARs. Similar trends were observed with dry mass and shoot length. Trace metals required for normal plant growth have been implicated in the reduction of glyphosate efficacy. This follows glyphosate’s original development as a metal chelator. Glyphosate-trace metal antagonism has recently sparked interest following co-application in glyphosate resistant soybeans. Molybdenum (Mo), an anion, may play a role at the physiological level on the antagonism of glyphosate. A greenhouse assay was carried out where seedlings grown from seeds (of susceptible commercial ryegrass cultivar (S biotype) and glyphosate resistant biotype (R biotype)) were grown with nutrient solutions containing 0x, 1x and 2x molybdenum (Mo) concentrations where 1x is 0.05 mg L-1 Mo. Glyphosate was applied at 0 (0x), 135 (1/4x), 270 (1/2x), 540 (1x) and 1040 (2x) g a.i. ha-1 rates. In the R biotype applying 2x Mo resulted in 0% survival in the R biotype at 1x GAR compared to 50% and 90% survival at the same GAR with 0x and 1x Mo. In terms of dry mass and shoot length the results did not show any conclusive trends.<br>AFRIKAANSE OPSOMMING: Glifosaat is ‘n baie belangrike onkruiddoder wat in verskeie onkruidbeheerstelsels gebruik word. Dit is as gevolg van verskeie positiewe eienskappe waaroor dit besit onder andere sistemiese werking, wye spektrum van onkruidbeheer en omgewingsvriendelike werking. Die onkruiddoder se effektiwiteit en gebrek aan residuele aktiwiteit is dus belangrik om bevredigende onkruidbeheer te bewerkstellig sonder om skade aan die omgewing te veroorsaak. Ten spyte van hierdie voordelige eienskappe het glifosaat ook tekortkominge. Vanaf 1996 is ontwikkeling van weerstand teen glifosaat in onkruide ‘n groot bron van kommer. Daar is egter ook ander faktore wat die maksimum potensiaal van glifosaat strem. Enige faktore wat die effektiwiteit van glifosaat strem mag veroorsaak dat die teikenplant aan subletale dosisse van glifosaat blootgestel word. Dit mag weer daartoe lei dat sulke plante blootgestel word aan die ontwikkeling van weerstand. Sommige faktore wat die effektiwiteit van glifosaat mag strem en dus moontlik kan lei tot seleksie vir weerstand is in hierdie studie ondersoek. Alhoewel glifosaat ‘n na-opkoms middel is kan die effektiwiteit moontlik beïnvloed word deur grondfaktore en nutriënte. Hierdie moontlikheid is ondersoek in ‘n glashuisstudie waarin raaigras (Lolium spp.) gebruik is. In hierdie studie is raaigras geplant in drie verskillende grondsoorte nl. suiwer sand (SS), grond vanaf ‘n weidingskamp (PS) en grond vanaf ‘n gewasland (CS). Die gronde het gevarieer in terme van nutriëntinhoud en alhoewel al drie gronde as sand geklassifiseer is, was daar tog verskille in fisiese eienskappe. Hierdie afdeling het uit vier eksperimente bestaan. In die eerste eksperiment is die invloed van verskillende gronde (PS, CS en SS) waarin die kommersiële raaigras kultivar geplant was op die effektiwiteit van glifosaat (360 g a.b. L-1 formulasie) teen vyf verskillende dosisse (GAR) ondersoek. Die dosisse was 0 (0x), 67.5 (1/8x), 135 (1/4x), 270 (1/2x) and 540 (1x) g a.b. ha-1. Die tweede eksperiment het die invloed van twee grondsoorte (PS en CS) waarin ‘n vatbare kommersiële raaigras kultivar en ‘n glifosaat weerstandbiedende raaigras biotipe geplant is, se invloed op die effektiwiteit van glifosaat ondersoek. Die dosisse was 0 (0x), 270 (1/2x), 540 (1x), 1080 (2x) and 2160 (4x) g a.b. ha-1. Die derde en vierde eksperimente was soortgelyk aan die eerste eksperiment behalwe dat die derde eksperiment die invloed van voeding (suiwer gedistileerde water teenoor ‘n gebalanseerde voedingsoplossing) saam met besproeiing ondersoek het. In die vierde eksperiment is die grondwerking van glifosaat wat as blaarbespuiting toegedien is ondersoek deurdat sommige potte wat gespuit is se oppervlakte met ‘n laag watte bedek is tydens die spuitproses en dadelik na spuit verwyder is teenoor die ander behandeling waar die grondoppervlakte nie bedek is nie. Die resultate het getoon dat i) grondtipe die effektiwiteit van glifosaat beïnvloed met beter beheer (19% oorlewing) in die PS grond vergeleke met 50% en 62% oorlewing in die CS en SS grondtipes respektiewelik. Hierdie effek kan moontlik beïnvloed word deur die weerstandsvlak van spesies omdat ii) die effek in die weerstandbiedende biotipe omgekeer is met ongeveer 95% oorlewing in the PS grondtipe vergeleke met 78% in die CS grondtipe; iii) effektiwiteit van glifosaat is beïnvloed deur die voedingstatus van die grond en die besproeiingswater. Dit word aangedui deur die afname in beheer van raaigras (100% oorlewing) wat in SS grond gegroei het en met suiwer gedistilleerde water besproei is vergeleke met 45% oorlewing in dieselfde grond wanneer met ‘n gebalanseerde voedingsoplossing besproei is. Plante wat in PS grond gegroei het het geen betekenisvolle verskille tussen die besproeiingsbehandelings getoon in hulle reaksie op glifosaattoediening nie, waarskynlik as gevolg van die inherente hoër nutriëntinhoud van die grond en iv) glifosaat effektiwiteit word beïnvloed deur die hoeveelheid glifosaat wat die grond bereik en deur die wortels opgeneem word. Dit is bewys in plante wat in PS grond gegroei het waar 93.3% plante oorleef het waar die grondoppervlakte bedek was teenoor 60% oorlewendes waar die grondoppervlakte nie bedek was nie indien glifosaat teen 1/8x toegedien is. ‘n Soortgelyke tendens is by die 1/4x dosis waargeneem. ‘n Teenoorgestelde effek is in SS grond waargeneem waar die oorlewingspersentasie in bedekte en onbedekte grond by 1/4x glifosaatdosis 0% en 40% onderskeidelik was. Glifosaat is aanvanklik aangeprys as ‘n omgewingsvriendelike onkruiddoder omdat dit vinnig in grond afgebreek word en omdat dit geadsorbeer word aan metale in die grondmatriks. In teenstelling hiermee is daar egter verslae in die literatuur wat dui daarop dat glifosaatresidue in die grond gewasopbrengste kan verlaag. In die gemelde studies is gevind dat fitotoksisiteit van glifosaat residue afhang van grondeienskappe en grondvrugbaarheid. Na aanleiding hiervan is ‘n glashuisstudie uitgevoer waarin die fitotoksisiteit van residuele glifosaat op ‘n kommersiële raaigraskultivar wat in PS, CS en SS gronde groei, ondersoek is. Glifosaat is op die grond in potte toegedien teen 0 (G1), 540 (G2) and 3240 (G3) g a.b. ha-1. Raaigras saailinge is daarna in die potte ingeplant twee ure, drie weke en vier weke nadat die glifosaat toegedien is. Bewys van grondaktiwiteit van glifosaat is gelewer deur die vermindering in persentasie oorlewing van die saailinge met toediening van glifosaat. Die vermindering in oorlewing was betekenisvol in die SS grond waar ongeveer 60% en 48% oorlewing van saailinge was by G2 en G3 dosisse onderskeidelik teenoor 100% oorlewing in die onbehandelde kontrole. Die afname in persentasie oorlewing is deur tyd beïnvloed deurdat die G2 dosis slegs by die twee ure behandeling betekenisvolle verlaging in oorlewing veroorsaak het terwyl die G3 dosis by die twee ure sowel as die drie weke behandeling betekenisvolle verlagings veroorsaak het. Vier weke na toediening was daar geen effek van glifosaat op die saailinge in enige van die gronde gewees nie. Soortgelyke tendense is waargeneem by die droëmassa en lengte data. Spoorelemente wat noodsaaklik is vir normale plantgroeiprosesse is al geïmpliseer in verlaging van glifosaat effektiwiteit. Dit is waarskynlik omdat glifosaat oorspronklik ontwikkel is as ‘n metaal cheleerder. Glifosaat-spoorelement antagonisme was onlangs in die nuus nadat glifosaat saam met sulke elemente toegedien is op glifosaat weerstandbiedende sojabone. Molibdeen (Mo), ’n anioon, mag ’n rol op fisiologiese vlak speel in doie effektiwiteit van glifosaat. ‘n Glashuisstudie is uitgevoer waarin saailinge van ‘n glifosaat vatbare kommersiële raaigras kultivar en ‘n glifosaat weerstandbiedende raaigras biotipe besproei is met voedingsmengsels wat 0x, 1x en 2x Mo bevat waar 1x 0.05 mg L-1 Mo is. Glifosaat is op die plante toegedien teen 0 (0x), 135 (1/4x), 270 (1/2x), 540 (1x) and 1040 (2x) g a.b. ha-1 dosisse. Die 2x Mo toediening het gelei tot 0% oorlewing in die R biotipe by 1x GAR vergeleke met 50% en 90% oorlewing by dieselfde GAR met 0x en 1x Mo. In terme van droëmateriaal en lengtegroei was daar geen konkrete tendense nie.

This study was undertaken to research the principles and practices behind increased pasture productivity on Longslip Station, Omarama. A range of landscape - soil - climate - plant systems were identified, then analysed and the legume responses measured. By isolating cause and effect and appreciating the driving variables of each system, lessons learnt could be reliably and objectively transferred to the rest of the farm. Extrapolation to the balance of the property (15,150 ha) permitted immediate large-scale development and engendered confidence to lending institutions, Lands Department, catchment authorities and ourselves. Soil (land) cannot be well managed and conserved unless it is mapped reliably and its characteristics measured and interpreted by skilled observers (Cutler, 1977). Soil resource surveys, and their interpretation, are an essential ingredient of rational resource evaluation and planning. This thesis is a figurative and comparative survey and study of the soil catenary bodies, resident vegetation, legume establishment and pasture production characteristics of a 400 hectare catchment, in relation to, and as influenced by soil landscape unit, slope component, altitude, aspect and time. The inherent diversity in landform, soil properties and vegetation communities in a single catchment in the high country has not previously been fully studied or appreciated. This has lead to blanket recommendations for fertilizer, seed and management regimes both within and between properties and even regions. This study reports on the diversity of, yet predictable change in soil properties with slope position (upper, middle and lower) aspect and altitude in terms of both soil physical properties e.g. soil depth and water holding capacity and soil chemical properties such as pH, BS%, %P, %S, %N and %C. The composition of the resident vegetation and its differential response to oversowing and topdressing and subsequent change through time is reported and discussed. Finally an epilogue gives an insight into the problems and frustrations of farming practices in the high country from a motivation and personal perspective and political point of view that it is essential to come to terms with.

This thesis describes the efforts of Russia's central government, local governments (zemstvos) and various social institutions to modernize peasant agriculture during the period 1906-17. The focus is on the micro-economic dynamics of the development program, on the interaction between various types of extension workers and peasant farmers. After a short discussion of Russia's economic backwardness at the beginning of the 20th century, the thesis examines the nature of rural society and the technological characteristics of peasant agriculture. The agricultural development program which evolved after 1906 is divided into three inter-related branches: land reform, social agronomy and cooperation. The land reform (consisting of resettlement, increased gentry land sales to the peasantry, privatization of peasant allotments and consolidation of strips into consolidated farmsteads) is examined in terms of quantitative results and social dynamics. We look at the strategies of the cadres pushing through the reform, the reaction of the peasantry and the effects of the reform on peasant farming. Social agronomy (mass agronomic education) was an innovative program administered jointly by the Ministry of Agriculture and the zemstvos; We examine in detail the work of local agronomists, their lifestyle and their effect on peasant society. Agricultural cooperation (agricultural societies, credit cooperatives, dairy cooperatives, etc.) experienced rapid growth during this time; we examine the role of cooperatives in providing farm credit, marketing services, farm supplies and agronomic advice to peasant farmers. Finally, the thesis describes the significant impact of the agricultural development program on agricultural technology and Russia's agricultural progress. The expansion of the farming sector in turn affected Russia's economy as a whole. In order to reinforce the hypothesis that the agricultural development program was directly responsible for a large part of Russia's agricultural expansion, we employ regression analysis on a database consisting of variables such as crop yields, land tenure, urbanization, etc. across 42 provinces of European Russia. The conclusion is that, in spite of its short life, the agricultural development program of 1906-17 succeeded in considerably improving the state of Russian agriculture.

Thesis (MScAgric)--University of Stellenbosch, 2001.<br>ENGLISH ABSTRACT: Potatoes is the fourth most important food source in the world. To provide in the ever increasing demand by the growing world population for this staple food, alternative ways will have to be found to produce a cheaper and a healthier end product. The tubers mainly consist of carbohydrates and starch, although 9% of the dry weight of the tubers consist of proteins. In its natural state the potato tuber is low in sodium and high in potassium and vitamin C. These proteins can provide in all the amino-acid requirements of humans and make it an outstanding balanced diet. The most important factor by which the production and quality of potatoes can be increased, is to provide better propagation material to producers. Minituber production is a relatively new method of producing better quality propagation material for producers. It is, however, very expensive because of the high capital investment needed. By producing more tubers per plant, or more tubers per square meter, the unit price per tuber may be lowered. The system commonly used for minituber production is where in vitro plants are planted in a greenhouse, usually in a vermiculite/peat mixture as medium. As in a hydroponic system, nutrients are added to the irrigation water. As possible strategy to increase the production of mini-tubers, the effect of nutrition was investigated. No significant differences were found in tuber production with small deviations in phosphorous and calcium nutrition. Researchers who reported significant differences in tuber production with nutrition, either corrected extreme shortages or induced it. By subjecting the root and tuber medium of potato plants to a pH-shock (nutrient solution with a pH of 3.5 for 10 hours), large amounts of tubers were initiated. A new production technique was developed where plants were grown in a hydroponic way without any root medium. In this way the right sized tubers could be removed without damaging the plant. Potato plants do not initiate tubers easily where stolons are not subjected to mechanical resistance. This problem was solved with the help of a pHshock, where significantly more tubers were formed per plant. The action of the pH-shock could be explained by a temporary inaccessibility of nutrients to the plant. Both calcium and magnesium absorpsion are hampered at a low pH, but calcium is also poorly translocated in the plant. Considering that a nutrient solution without calcium produced the same results as the pH-shock treatment in this study, one may make the assumption that an induced calcium shortage may be responsible for the low pH effect. The same effect may even be induced by giving the plants clean water for some time. Such a treatment was, however, not tested but should receive attention in further studies. The correct timing for a low pH-shock may need more research. A precise number of days after transplanting can not be prescribed since many factors such as light intensity, daylength and cultivar difference affect plant growth and tuber initiation. Environmental conditions, the physiological age and the biomass of the plant may affect the timing of the shock. A low pH-shock could not at any stage induce tubers in potato plants where unfavorable environmental conditions occurred. It seems as if the plants need to be ready for tuber initiation before the pH-shock can be successfully applied. By removing/harvesting the tubers at the required weight, the burden on the plant may be relieved enabling more tubers to form. It was experienced that the reproductive system of the potato plant is complex with a number of factors affecting it. The new production system has potential, but more developmental work is still needed.<br>AFRIKAANSE OPSOMMING: Aartappels is die vierde belangrikste voedelsoort in die wereld, Om te kan voorsien aan die ewigdurende verhoogde vraag na hierdie stapelvoedel deur die groeiende wereld-bevolking, sal daar maniere gevind moet word om die eindproduk goedkoper en in 'n gesonder toestand op die mark te plaas. Die knolle bestaan hoofsaaklik uit koolhidrate en stysel, alhoewel 9% van die droe gewig van knolle uit proteiene bestaan. Die aartappelknol is in sy natuurlike toestand laag in natrium en hoog in kalium en vitamien C. Hierdie protei'ene kan in al die aminosuur-behoeftes van mense voorsien wat dit dus 'n uitstekende gebalanseerde dieet maak. Die belangrikste faktor waarmee die produksie en kwaliteit van aartappels verhoog kan word is om beter voortplantingsmateriaal aan produsente te verskaf. Miniknolproduksie is 'n relatief nuwe manier om gesonde en groeikragtige voortplantingsmateriaal vinnig by die produsente te kry. Dit is egter 'n duur metode omdat die kapitaal-investering groot is. Deur meer knoUe per plant, of meer knolle per vierkante meter te produseer kan die eenheidsprys per moer verlaag word. Die sisteem wat algemeen vir miniknolproduksie gebruik word is om in vitro plantjies in 'n kweekhuis, gewoonlik in 'n vermikulietldennebas mengsel te plant. Voedingstowwe word dan soos in 'n hidrokultuurstelsel saam met die besproeiingswater toegedien. As moontlike strategie om die produksie van miniknolle by aartappels te verhoog, is die invloed van voeding daarop ondersoek. Daar is gevind dat daar nie groot verskille in knolproduksie met klein afwykings in fosfaat- en kalsium-voeding veroorsaak is nie. Navorsers wat wel betekenisvolle verskille III knolproduksie met voedingsbehandelings verkry het, het ekstreme tekorte reggestel of gemduseer. Deur die wortel- en knolmedium van aartappelplante aan 'n pH-skok (voedingsoplossing met 'n pH van 3.5 vir 10 ure) bloot te stel, is daar gevind dat 'n groot hoeveelheid knolle geinisieer word. Verder is 'n nuwe produksietegniek ontwikkel waar die plante met 'n suiwer waterkultuur metode geproduseer word, sodat knolle wat oesgereed is verwyder kan word. Aartappelplante inisieer nie maklik knolle onder hierdie omstandighede waar stolons geen meganiese weerstand ervaar nie. Met behulp van die pH-skok het daar betekenisvol meer knolle per plant gevorm. Die werking van die pH-skok kan moontlik aan 'n tydelike ontoeganklikheid van voedingstowwe toegeskryf word. Beide kalsium en magnesium word moeilik by 'n lae pH opgeneem maar kalsium word boonop moeilik deur die plant getranslokeer. Aangesien 'n voedingsoplossing sonder enige kalsium dieselfde resultate as die pHskok gelewer het, lyk dit asof 'n geinduseerde kalsium-gebrek vir die lae pH effek verantwoordelik mag wees. Die skok kan makliker en veiliger toegepas word deur vir 'n tydperk net skoon water aan die plante te gee. So 'n behandeling is egter nie beproef nie maar behoort in opvolgwerk aandag te ontvang. Die optimum tyd waarop so 'n skok toegedien moet word is nog onduidelik. Daar kan nie op 'n eksakte aantal dae na uitplant gewerk word nie, aangesien daar te veel faktore soos ligintensieteit, daglengte en kultivar is wat plante se groei en knolinisiasie kan beinvloed, Omgewingstoestande, die fisiologiese ouderdom van die plant en die hoeveelheid biomassa wat gevorm het mag bepaal wanneer die plante geskok moet word. Waar ongunstige omgewingstoestande geheers het, kon 'n lae-pHskok op geen stadium knolinisiasie induseer nie. Dit wil voorkom asof die plant vir 'n knolinisiasie fase gereed moet wees voordat 'n lae-pH-skok doeltreffend is. Dit verhoog dan bloot die aantal knolle wat per plant ontwikkel. Deur die knolle op die verlangde grootte te pluk kan die las op die plante verlig word sodat meer knolle mag vorm. Daar is ervaar dat die reproduktiewe stelsel van die aartappelplant kompleks is en dat daar baie faktore is wat dit mag beinvloed. Die nuwe produksiestelsel toon potensiaal, alhoewel verdere ontwikkelingswerk nog nodig is.

Master of Science<br>Department of Agronomy<br>Nathan O. Nelson<br>Increasing nitrogen use efficiency (NUE) and nitrogen response in winter wheat could help producers reduce input costs associated with nitrogen fertilizers and decrease the negative environmental impacts of N loss. The objectives of this research were to i) establish if there are genetic differences in NUE and other related parameters among wheat varieties commonly grown in the Great Plains, ii) determine if there are differences in N response among select varieties with a range of NUEs, and iii) determine if NUE influences N response. This information could be useful in future breeding efforts as researchers seek to develop more efficient varieties. This was approached by conducting two separate studies, a large NUE study with 25 winter wheat varieties, and a smaller N Rate study with 4 varieties that represented a range of NUEs based on the preliminary results of the NUE study. The NUE study was conducted over the course of several seasons and locations, with treatments of consisting of N Rate and variety. The experiment was laid out in a strip-plot design and replicated four times at each location. In the 2010-11 and 2011-12 seasons it was planted at the Kansas River Valley Experiment Field in Rossville, KS. In the 2012-13 season the experiment was planted at two locations, one at Silverlake and another at Ashland Bottoms, KS. The experiment was again planted at two locations in the fall of 2013, in Ashland Bottoms, KS, and Hutchinson, KS. The wheat varieties were grown with two N rates, 0 kg N ha⁻¹ and 90 kg N ha⁻¹. Nitrogen use efficiency was calculated as the grain yield per unit of available nitrogen (sum of soil N and fertilizer N) and ranged from 22-30 kg of grain per kg of N and was strongly influenced by variety with a p<0.001. Several other related parameters, such as grain yield, nitrogen utilization efficiency, harvest index, and fertilizer use efficiency were also significantly affected by variety with a p<0.05. These data suggest there are significant genetic differences in how varieties use and transport nitrogen within their tissues to produce grain. The N Rate experiment was planted in two locations during the 2012-13 season at Silverlake and Ashland Bottoms, KS, and planted again in the fall of 2013 at Ashland Bottoms and Hutchinson, KS. This experiment was laid out in a split-plot design with four varieties and four nitrogen rates. The varieties selected for this study were Duster, Everest, Jagger, and Larned and the four N rates were 0, 33.6, 89.7, and 145.7 kg N ha⁻¹. The results showed significant differences in yield response among the varieties at only one location, Ashland Bottoms (p=0041). Although N response at Silverlake was not significant, mean grain yields between varieties was significant (p<0.001). Two additional parameters, NUE and harvest index (HI), were also significantly different between varieties at Silverlake, KS with a p<0.05, while no additional parameters were significant at Ashland Bottoms. Those varieties that had higher response, Everest and Jagger, also tended to have higher NUEs compared to the other two varieties, Duster and Larned. However, because of the contrasting results between locations, additional research is needed to develop firm conclusions. These results provide significant evidence to support varietal differences in nitrogen use due to genetics, and provide the opportunity for breeders to begin developing varieties with higher NUE and improved N response. However, additional research will be required to determine the specific traits responsible for these varietal differences and to determine the suitability of high NUE crops for meeting the nutritional requirements of the future.

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<p> With the development of transgenic crops resistant to auxin herbicides will come an increase in the use of these herbicides for weed control. This new technology will greatly aid growers that have glyphosate-resistant weeds such as Palmer amaranth (<i>Amaranthus palmeri</i> S. Wats) in their fields. A challenge will be with farmers that choose not to use this new technology and have susceptible crops on their farm or adjoining farms. Auxin herbicides such as 2, 4-D and dicamba are well-documented as being very injurious to susceptible crops, even at low doses. It is for this reason that research is being conducted to compare the differences in the amount of particle drift with hooded boom sprayers compared to open boom sprayers. Along with this research, various droplet sizes will also be analyzed and compared between the two sprayers.</p><p>

Development of maize, Zea mays L., germplasm resistant to the European corn borer, Ostrinia nubilalis (Hubner) and Fusarium fungal pests has been in progress for more than three decades as a worldwide cooperative effort. Some of the host plant resistance to the European corn borer and Fusarium has been attributed to the phytochemical product 6-methoxybenzoxazolinone. However, it has been shown that seasonal weather impacts concurrently on maize development, corn borer and Fusarium phenology. It was hypothesized that some of the maize resistance to both pests depended directly on climatological conditions. In the United States, genotype selection for first generation borer resistance is achieved during June infestations using leaf feeding assessment. In Canada, first selection began at the silk stage of plant development in July. The second genotype selection is conducted at grain harvest in October by plant dissections. The larval population, number of tunnels and tunnel length in the first 30 cm of the stalk above the soil surface were used to differentiate genotype susceptibility to corn borers. Grain moisture was directly correlated with genotype resistance to corn borer. Fungi encountered comprised Fusarium moniliforme, F. graminearum, F. sporotrichioides, F. oxysporum, F. avenaceum, and F. equiseti. Two species, F. moniliforme and F. equiseti, were recovered throughout the season. These fungi were first recovered from pollen caught in the leaf collar sheath. As the leaf sheath of maize is relaxed with plant development, the Fusarium contaminated soil and the pollen run down past the ligule by wind, rain splash, and insect movement to settle within the sheath cavity. Undamage pith samples (by the borer) taken at grain harvest showed sporadic tissue contamination by Fusarium. Oppositely, as the corn borer larvae migrated downward on the plant, they drilled the collar sheath, the stalk rind and dug galleries in the stalk to feed on the pith tissue to complete their development. Consequently, the larvae and borer tunnels were repeatedly contaminated with Fusarium. It was shown that pith tissues were initially colonized by primary fungi such as F. equiseti which initiate pith breakdown; then these fungi were overgrown by more competitive species such as F. moniliforme or F. sporotrichioides. Correlation of the stalk rot incidence to genotype maturity and the stalk rot incidence to grain moisture were both negative and significant; indicating that physiological activity during October protected the stalk against fungi infection. It was hypothesized that genotype maturity based on the heat unit rating (given by companies) or grain moisture at harvest (indicator of genotype maturity) were the two common factors related to Fusarium stalk rot resistance. (Abstract shortened by UMI.)

Wheat growth appeared to be similar with the different N-fertilizers. However, a tendency for more growth was observed under nitrate and a mixed nutrition. The supply of ammonium, a mixture of ammonium and nitrate or urea resulted in an acidic pH in the rhizosphere. Nitrate uptake by plants resulted in a pH increase of the rhizosphere. The amounts and types of amino acids in the rhizosphere were significantly (P 0.05) different under the various N-fertilizers. In the wheat rhizosphere supplied with nitrate the total amino acids were less than those of plants supplied with the other N-fertilizers. The greatest total amount was observed under ammonium supply. In the case of nitrate-fed plants there were more basic amino acids in the rhizosphere whereas, plants supplied with other N-fertilizers exuded more acidic amino acids. The amount of amino acids decreased with time. The different forms of N-fertilizers also produced different effects on the amounts and types of both soluble and insoluble sugars in the rhizosphere. (Abstract shortened by UMI.)

The infection of soybean roots by the soil bacterium Bradyrhizobium japonicum results in the formation of specialized organs on the roots called nodules. Within the nodules, a differentiated form of the bacterium (the bacteroid) reduces atmospheric nitrogen to ammonia. Nodule development involves a complex interaction requiring the coordinated expression of nodule-specific bacterial (bacteroidin) and nodule-specific plant (nodulin) genes. A number of nodulin gene products from soybean have been characterized, but the functional roles of only a few have been determined. This thesis describes the isolation and characterization of four nodule-specific cDNA clones (and a leghemoglobin clone) from a cDNA library that was derived from soybean nodule poly (A)$\sp+$ enriched RNA. mRNA corresponding to these cDNA clones, could be detected in RNA isolated from the soybean nodule; but could not be detected in RNA isolated from the root. The pattern of expression of the genes corresponding to the cDNA clones was investigated at various times following infection of the soybean Glycine max (L.) Merrill by Bradyrhizobium japonicum. It appears that these nodulin mRNAs are expressed just prior to the onset of nitrogen fixation and accumulate to their maximum levels shortly thereafter. Sequence characterization of the four clones indicated that they represented members of a previously described nodulin multi-gene family: the "Nodulin A" family (Verma and Delauney, 1988). The "Nodulin-A" family represents a group of abundantly transcribed nodulins, whose function is unknown. Three of these clones, 9-11-B, 36-1-A, and 6-9-F, support the previously published sequences of nodulin-23 (Mauro et al., 1985; Sengupta-Gopalan et al., 1986), nodulin-22 (Sandal et al., 1987), and nodulin-44 (Sengupta-Gopalan et al., 1986) respectively. A fourth clone, 15-9-A, represents a new member of this multi-gene family. Northern blot hybridization with oligo-nucleotide probes specific to this cDNA clone, indicates that 15-9-A represents an abundantly transcribed 1 kb mRNA. Our analyses suggest that 15-9-A is a member of a subfamily of three closely related genes within the larger "Nodulin-A" family. 15-9-A is related to the nodulin-20 sequence of Sandal et al. (1987), which our analyses show is also a member of this subfamily. The 15-9-A cDNA is 100% identical to nodulin-20 in the region that is 5$\sp\prime$ to the position of the nodulin-20 intron, and 89% similar in the region that is 3$\sp\prime$ to the intron. Although the region of greatest divergence between the two sequences is in the 3$\sp\prime$ coding region, each sequence codes for a proline-rich carboxy terminus. In addition, we have determined that a 0.8 kb mRNA that cross-hybridizes to 15-9-A represents a third gene within this subfamily. We have also detected the presence of "Nodulin-A"-like sequences in the DNA of alfalfa, several actinorhizal plants, spinach, and corn. This raises the possibility that "Nodulin-A" like sequences have a functional role in plants other than soybean. We have isolated four alder genomic clones which cross hybridize to the cDNA clone 9-11-B, as an approach to characterizing a "Nodulin-A" sequence from another plant. Further characterization of these clones should determine their relatedness to the soybean sequences and may provide clues as to their possible functional significance.

Estimates of genetic diversity present in gene pools have important implications for breeders and germplasm curators. They constitute the raw material for plant improvement and can provide protection against genetic vulnerability to biotic and abiotic stresses. The purpose of this thesis was to derive Pedigree and Amplified Restricted Fragment Polymorphism (AFLP)-based Genetic Diversity Estimates (GDEPED and GDEAFLP, respectively) among all currently registered 13 Canadian durum wheat cultivars in order to test the hypothesis that the actual level of genetic variation at the DNA level is lower than what is measured from pedigree data. Two objectives were set in this thesis. The first objective was to estimate the genetic diversity level among cultivars using two independent methods namely AFLP and pedigree. The second objective of this thesis was to use cultivar-specific AFLP markers for identification of cultivars and transform these markers into sequence tagged site (STS) markers for routine identification of durum wheat cultivars. (Abstract shortened by UMI.)

The Senegal River Basin (SRB), located in the Sahel region of West Africa is undergoing fundamental environmental, hydrologic and socio-economic transitions simultaneously. The tri-nation (Senegal, Mauritania and Mali) river basin development authority, the Organisation pour la Mise en Valeur du Fleuve Senegal (OMVS) is attempting to execute a shift to irrigated rice production in the river basin for domestic consumption, to ease the severe foreign exchange shortfalls these riparian nations face. Compounding the severe effects of the drought on the river basin ecology is the negative impact of the state imposed agricultural policy of rice production. Rice production in the arid river valley has been a financial and social failure. This study postulates an alternative utilization of the scarce water resources in the basin. The water demand pattern for an alternative natural resources management focused agricultural development policy is based on the irrigation water requirements of well-researched village-scale irrigation projects in the SRB, and intensive irrigated agro-forestry projects. The agro-forestry production system analyzed has the joint objectives of using irrigation to re-establish a protective, diverse and productive bio-mass cover in the desertifying river valley, and to reverse the tide of drought induced migration from rural to urban areas. A comparative river system simulation study was conducted to analyze the effects of both the rice production development policy (policy RP) and the natural resources management policy (policy NRM), on the full agricultural development potential of the SRB. Alternative hydrologic scenarios were generated for the simulation study according to the Senegal River time series analysis, for the historical level, 1970s level drought and 1980s level drought. For all hydrologic scenarios the lower over-all demand pattern exerted by policy NRM allowed a higher full development potential than for policy RP. (Abstract shortened by UMI.)

By means of ANOVA, Duncan's test Student's t test and linear regressions, it was demonstrated that there was no significant correlation between the quantity of gramine and the morphological characters considered (geographic origin, spike row number, spike form, cultivation season, glume length, yield, water content of fresh leaves, seed mean mass, and seed colour). By "Duncan's multiple range test" it was shown that there was a significant (F = 26,81; P 0.0001) variation in gramine content between the different genotypes (minimum = 0 & maximum = 2674). However, canonical discriminant analyses and "cluster"ing by the MODECLUS procedure failed to provide justification for grouping of varieties susceptible to aphid attack, leading to the conclusion that gramine content cannot be sufficiently closely related to morphological characters to serve as a basis for taxonomy. Finally, additional experimentation revealed that the presence of gramine alone is often not sufficient to confer protection against aphid attack, and other factors must be considered, such as anatomy or the existence of other protective constituents. Such research could lead to the development of new resistant biotypes. (Abstract shortened by UMI.)

Of 40 identified phytoseiid mites which occur in Burundi, only Eseius fustis was regularly observed on cassava, whereas E. talinga and E. bwende were rarely present. Iphiseius degenerans was also observed but not as frequently as E. fustis. Predatory insects (Holobus fageli, H. pallidicornis, Stethorus aethiops, S. fujunus and some families like Chrysopidae, hemerobiidae and Anhocoridae) were recorded on cassava during CGM outbreaks. Of two predatory phytoseiids introduced (Typhlodromalus limonicus and Neoseiulus idaeus) and released twice during the study period on two varieties of cassava (Nakarasi and Mpambayabashengera), only one was recovered in the rainy season when the CGM population is normally low. This may indicate its potential use as a biological control agent. Mean mite densities, leaf damage, pubescence and leaf cyanide content of twenty cassava varieties were evaluated for resistance. Pubescence was negatively correlated with leaf damage (r = $-$0,46; p 0.05) whereas no relation was found between cyanide and leaf damage. (Abstract shortened by UMI.)

This study focuses on switchgrass, Panicum virgatum L., a North American tallgrass prairie species that has been used in agriculture for only 50 years. We hypothesized that wild variants of this species are more mycorrhizal dependent than the cultivars due to selection against mycorrhizae in agricultural conditions. Mycorrhizae, naturally occurring associations between roots and symbiotic fungi, are known to benefit plants in most environments. These associations have been proposed as a means for crop improvement in agriculture. However, current agricultural practices tend to diminish the potential for crops to benefit from mycorrhizae. Two greenhouse experiments with a factorial design were performed using switchgrass inoculated or not with Glomus intraradices Schenck and Smith. In the first experiment, four wild varieties (PH, ONP, Ojibway and Pterophylla) and six cultivars (Forestburg, Summer, Shelter, Caddo, NU and Trailblazer) were grown for 12 weeks. From those, 3 wild types (PH, ONP and Ojibway) and 3 cultivars (Forestburg, Caddo and NU) were chosen for the second experiment. Switchgrass plants were analyzed for various physiological, root and mineral parameters in order to assess their overall mycorrhizal dependency (MD). (Abstract shortened by UMI.)

This thesis describes the investigation of the bioactivity of triterpenoids, limonoids and spiro-triterpenoids, isolated from the order of the Rutales. The focus of this research has been towards the development of botanical insecticides with non-neurotoxic modes of action in insects. It follows the recent development of Neem (Azadirachta indica, Meliaceae) as a botanical insecticide containing a limonoid azadirachtin as its main active compound. Because so few Meliaceae members have been examined for insecticidal activity the project was initiated by the screening of over sixty ethanol extracts of various parts of twenty species (collected from Costa Rica and the Tropical Museum in Miami, Florida) for bioactivity against the European corn borer (Ostrinia nubilalis) and the Variegated cutworm (Peridroma saucia). The data suggest that a majority of the extracts studied inhibited growth significantly; some are more active than neem leaf extracts. Swietenia mahogani bark, Trichilia glabra bark, T. hirta leaves, T. americana bark, T. trifolia wood, T. pleana and Azadirachta indica wood showed potent activity against the cutworm. Ruptiliocarpon caracolito bark, Cedrela odorata leaves, Aphanamixis polystachys wood, T. glabra wood and T. pleana bark showed good activity against the corn borer larvae. Bioassay guided fractionation of the most active crude extract, the bark of Ruptiliocarpon caracolito, has resulted in the isolation of six very novel spiro-CD-triterpenoids, the spirocaracolitones. The spirocaracolitones, at 100 ppm, were screened for antifungal activity against Fusarium using a hyphal growth bioassay. After 48 h a high degree of inhibition of growth (59-79%) was observed. These novel triterpenoids exhibited no antimalarial activity when screened against Plasmodium falciparum. A study of the effects of these compounds, incorporated into artificial diet, on the neonate life cycle of the European corn borer was conducted. All the spirocaracolitones effected the growth and the development of the insects but spirocaracolitone B and spirocaracolitone C were substancially more active than the other spirocaracolitones. Two postulates dealing with the biosynthesis of these unique spiro-compounds are also presented. Both commence with a friedelin derivative because canophyllol was isolated in large quantities from the hexane extract. They envisage generation of a carbocation at C12 followed by migration of the C23 methyl group this results in the formation of a carbocation at C13. The spirosystem results from migration of the C8-C14 bond. An investigation of the structure/activity relationships of gedunin was conducted to determine the moieties responsible for its antimalarial and/or antifeedant properties. Ten derivatives of gedunin were prepared (1,2-dihydrogedunin, 1,2-epoxygedunin, 1,2-dihydro-3$\beta$-gedunol, 3$\beta$-acetoxy-1,2-dihydrogedunin, 7-deacetylgedunin, 7-ketogdunin, hexahydrogedunin, tetrahydrogedunin, 21-acetylgedunin, 23-acetylgedunin) along with five other limonoids (limonin, epilimonol, nomilin, obacunone, hirtin) closely related to gedunin were evaluated for antifeedant activity (Ostrinia nubilalis) and antimalarial activity (Plasmodium falciparum). Evaluation of these compounds for antimalarial activity presented no increase in activity however it was clearly determined that alterations to the enone in ring A and at C7 of gedunin resulted in large losses of activity. Evaluation of the effects of these limonoids on the neonate life cycle of the European corn borer at 5 and 50 ppm incorporation into the artificial diet did lot produced dramatic effects on the growth and development of the larvae. At these concentrations structure/activity relationships could not be proposed.$\sp*$ ftn$\sp*$Please refer to the dissertation for diagrams.

The purpose of this research is to describe and analyze the present and potential role of non-governmental organizations (NGO's) in the management of agricultural soil erosion and associated water quality decline (ASEWQ), in Ontario. A series of five tasks are associated with this research purpose. These tasks include: the cataloguing of all agricultural NGO's in Ontario; the assessment of this NGO population's vertical interaction; the assessment of the NGO population's horizontal spread; analysis of NGO mobilization potential in the area of ASEWQ management; and finally the characterization of degree of NGO favourability towards, and involvement in, ASEWQ management. Research has led to the discovery of a very large and complex population of agricultural organizations in Ontario. The horizontal distribution of this population closely reflects the geographic configuration of agricultural activity in the province. The vertical distribution reveals a high degree of organizational affiliation and networking which gives the grassroots indirect access to provincial policy influence. Despite the size, complexity and general favourability of this population towards soil conservation, few NGO's have suitable potential to mobilize on the ASEWQ issue. As a result, only a few strategically placed and organized NGO's have any involvement in controlling agricultural soil erosion. In conclusion, this research offers a series of recommendations to provincial government agricultural policy makers and future research avenues. (Abstract shortened by UMI.)