Dissertations / Theses on the topic 'Agronomic measurements'

A two year study was conducted to determine the optimum timing of the initial post-plant irrigation for cotton (Gossypium hirsutum L.). A short-season Upland variety, DPL 20, was planted on 19 April 1993 and 15 April 1994 at the Marana Agricultural Center. Daily midday leaf water potential measurements were taken using the pressure chamber technique. Treatments, designated T1, T2, and T3, received the initial post-plant irrigation when the midday LWP measured -1.5, -1.9, and -2.3 MPa, respectively. Soil-water data was collected at 25 cm depth increments using neutron attentuation. Yields were 1263, 1244, and 1110 kg lint/ha in 1993 and 1229, 1176, and 1095 kg lint/ha in 1994 for T1, T2, and T3, respectively. When treatments were initiated, approximately 84 (T1), 62 (T2), and 32% (T3) of the total plant-available water was present in the upper 150 cm of the soil profile.

A data acquisition system to collect soil moisture readings at 60 field locations was developed. The system predicted a resistance value from a measured counts per time. An error was associated with the measured counts and time, however, this error was minimized by increasing the time for resistance measurement. The effect of temperature was minimized by an automatic calibration of the system before collecting readings. The Watermark electrical resistance moisture sensor was used to sense water content. The system, including eight sensors, was tested in the field. The data collected was difficult to explain. An evaluation of the Watermark sensors indicated a large variation from sensor to sensor, and also indicated a marked influence of soil texture on sensor resistance.

A comparative study was performed to investigate the tolerance levels of beet armyworm to three insecticides, cyfluthrin, profenofos, and methomyl. The field strains were collected from Yuma and Marana, AZ whereas the susceptible laboratory strain was obtained from California. Dosage-mortality data were obtained by topical application on third instar larvae. Compared to the susceptible strain, both Yuma and Marana strains exhibited an increase in the LD50 to cyfluthrin by 15.65 and 5.45-fold, respectively. Both strains also exhibited an increase in the LD50 to profenofos and methomyl by 14.10, 17.77 and 2.95, 8.07-fold, respectively. The cyfluthrin-selected strain (Marana strain) tested for cross resistance to profenofos and methomyl and exhibited an increase in LD50 by 24.68 and 3.32-fold,respectively.

Doctor of Philosophy<br>Department of Agronomy<br>Charles W. Rice<br>Nitrogen is critical for plant growth and is a major cost of inputs in production agriculture. Too much nitrogen (N) is also an environmental concern. Agricultural soils account for 85% of anthropogenic N₂O which is a major greenhouse gas. Management strategies for N fertilization and tillage are necessary for enhancing N use efficiency and reducing negative impacts of N to the environment. The different management practices induce changes in substrate availability for microbial activity that may result in increasing or reducing net N₂O emitted from soils. The objectives of this research were to (1) integrate results from field studies to evaluate the effect of different management strategies on N₂O emissions using a meta-analysis, (2) quantify N₂O-N emissions under no-tillage (NT) and tilled (T) agricultural systems and the effect of different N source and placements, (3) perform sensitivity analysis, calibration and validation of the Denitrification Decomposition (DNDC) model for N₂O emissions, and (4) analyze future scenarios of precipitation and temperature to evaluate the potential effects of climate change on N₂O emissions from agro-ecosystems in Kansas. Based on the meta-analysis there was no significant effect of broadcast and banded N placement. Synthetic N fertilizer usually had higher N₂O emission than organic N fertilizer. Crops with high N inputs as well as clay soils had higher N₂O fluxes. No-till and conventional till did not have significant differences regarding N₂O emissions. In the field study, N₂O-N emissions were not significantly different between tillage systems and N source. The banded N application generally had higher emissions than broadcasted N. Slow release N fertilizer as well as split N applications reduced N₂O flux without affecting yield. Simulations of N₂O emissions were more sensitive to changes in soil parameters such as pH, soil organic carbon (SOC), field capacity (FIELD) and bulk density (BD), with pH and SOC as the most sensitive parameters. The N₂O simulations performed using Denitrification Decomposition model on till (Urea) had higher model efficiency followed by no-till (compost), no-till (urea) and till (compost). At the regional level, changes in climate (precipitation and temperature) increased N₂O emission from agricultural soils in Kansas. The conversion from T to NT reduced N₂O emissions in crops under present conditions as well as under future climatic conditions.

L'effetto dei gas serra sul cambiamento climatico ha portato molti esperti a considerare la riduzione delle emissioni di gas serra come strategia per il riscaldamento globale. In particolare tale fenomeno è causato dall’anidride carbonica (CO2), metano (CH4) e il protossido di azoto (N2O). E 'ampiamente accettato che la principale fonte antropica di gas a effetto serra (tranne CO2) è dovuta alle attività agricole. Lo scopo di questo studio è quello di definire concetti e strumenti per facilitare il settore agricolo a ridurre le emissioni di gas serra. In particolare, abbiamo posto la nostra attenzione ai sistemi di misurazione delle emissioni dal suolo, testando un nuovo sistema (SASSFlux) e le sue caratteristiche a confronto con due strumenti ampiamente utilizzati (Bruel & Kjaer e gascromatografia). Inoltre abbiamo testato due modelli di simulazione (DNDC e SPACSYS) valutando i dati simulati e quelli misurati su un esperimento effettuato su lisimetri. In fine abbiamo applicato le conoscenze acquisite in pieno campo per la valutazione delle emissioni di CO2 e N2O con diversi concimi e lavorazione del terreno. La tesi si propone di fornire una visione completa dei diversi aspetti da affrontare nella valutazione delle emissioni di gas serra provenienti da diversi scenari di gestione agricola.<br>The effect of greenhouse gases (GHG) on climate change led many experts to consider the reduction of GHGs emissions as a crucial strategy to tackle the predicted global warming. In particular, atmospheric warming is caused mainly by carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O). It is widely accepted that the main anthropogenic source of GHG (except CO2) is due to agriculture activities. The purpose of this study was to help define concepts and tools to facilitate agricultural sector to reduce greenhouse gas emissions. In particular we based our focus on measuring systems for CO2 emissions, testing the performance of novel system (SASSFlux) and its features in different condition with two widely used instruments (Bruel&Kjaer and gas chromatography). Moreover we testing two process-based models, DNDC and SPACSYS, evaluating their performance and the agreement between simulated and measured data on a experiment carried out on lysimeters. At the end we applied all the knowledge acquired on a field experiment evaluating CO2 and N2O emissions from different organic and mineral fertilizers and tillage. The complete thesis aims to provide a comprehensive view of the different aspects to be addressed in the assessment of GHG emissions from different scenarios of agricultural management.

Basic studies of seed germination and seedling emergence assume an important role within scientific researches due to the devastation and fragmentation of the native vegetation of the Cerrado. Thus, in the present study the processes of seed germination and seedling emergency were evaluated using the linear correlations among the measurements calculated for five Cerrado species. The individual contribution for the variability of the studied species and the contribution of each species in relation to the studied group were also quantified. For this purpose, hierarchical lineal models were used to determine the genetic parameters among individuals within the species. The diaspores were collected in the 2004/2005 crops, in a fragmented area of the Araguari river valley, MG. The experiments were carried out using newly-collected diaspores, being conducted in a germination chamber for germination and in a greenhouse covered with light reducing net for seedling emergency. The data collection was carried out every 24 hours, taking into account the protrusion of the embryo for the experiments set up in the laboratory and the emergence of any part of seedling above the substratum for experiments kept in greenhouse. The variability registered among the individuals of the studied species generated statistical differences in all aspects of the germination and emergency processes, indicating that the decision to mix the diaspores or not for the formation of the lots should be made after results of previous tests. High mean values were registered for germinability (G) and emergency percentage (E) for the majority of individuals studied, indicating the good physiological quality of the diaspores produced in the 2004-2005 crop. The seed germination and seedling emergence of Anadenanthera colubrina and Chorisia speciosa and the seedling emergence of Myracrodruon urundeuva were faster and synchronized, while those of Cedrela fissilis and Lithraea molleoides were slower, asynchronous and spread over time, indicating the presence of relative dormancy. These germination and emergence patterns were confirmed by means of positive linear correlations between E and Z (synchrony) and negative between E and U (uncertainty) for the synchronous events; negative correlations between E and Z and positive and E and U for the asynchronous. For C. speciosa the synchrony of germination was also expressed by the positive association between G and v (mean germination rate). The partition of the variability allowed one to verify that the germination process and seedling emergence present a pattern behavior intrinsic to each species, with more than 60% of the total variability attributed to the species. Above 0.80 of the heritability was registered for most of the characteristics evaluated, indicating that the largest proportion of the total variability is of genetic nature. High genetic variability, expressed by the CVg and detected for time, rate, and synchrony measurements was registered between the L. molleoides and C. fissilis individuals. The magnitude of the CVg values showed that genetic variation exists in the studied species in relation to the germination and emergency processes and then they should be included in conservation projects.<br>Os estudos básicos de germinação de sementes e emergência de plântulas assumem papel relevante dentro das pesquisas científicas diante da realidade de devastação e fragmentação da vegetação nativa do Cerrado. Em função disso, o presente trabalho teve por objetivos avaliar o processo de germinação de diásporos e a emergência de plântulas de cinco espécies do Cerrado do Planalto Central e, a partir de medidas desses processos, quantificar as correlações lineares entre as mesmas; quantificar a contribuição da variabilidade das matrizes para as espécies estudadas e de cada espécie em relação ao grupo estudado, utilizando-se modelos lineares hierárquicos e, estimar parâmetros genéticos entre matrizes dentro de espécies. Os diásporos foram coletados nas safras 2004/2005 numa região fragmentada do vale do rio Araguari, MG. Os testes foram realizados com diásporos recém-coletados de matrizes em separado, sendo os testes de germinação instalados em câmara de germinação e os de emergência em estufa coberta com telado redutor de luminosidade. A coleta dos dados foi realizada a cada 24 horas, observando-se a protrusão do embrião para os experimentos montados em laboratório e a emergência de qualquer parte da plântula acima do substrato para experimentos mantidos em estufa. Registrou-se variabilidade entre as matrizes das espécies estudadas em todos os aspectos do processo de germinação e emergência e, por isso, a decisão da mistura ou não dos diásporos para a formação dos lotes deve ser tomada após a realização de testes prévios. Foram registrados altos valores médios para germinabilidade (G) e porcentagem de emergência (E) para as matrizes estudadas, indicando a boa qualidade fisiológica dos diásporos produzidos na safra 2004-2005. Os processos de germinação de sementes e emergência de plântulas de Anadenanthera colubrina e Chorisia speciosa e de emergência de plântulas de Myracrodruon urundeuva foram mais rápidos e sincronizados, enquanto para Cedrela fissilis e Lithraea molleoides foram mais lentos, assíncronos e espalhados no tempo, indicando a presença de dormência relativa. Esse padrão de comportamento foi confirmado por meio das correlações positivas entre E e Z (sincronia) e negativas entre E e I (incerteza) para os eventos síncronos; correlações negativas entre E e Z e positivas entre E e I para os assíncronos. Para C. speciosa a sincronia da germinação também foi retratada pela associação positiva entre G e v (velocidade média). A partição da variabilidade permitiu verificar que o processo de germinação e emergência de plântulas apresenta padrão de comportamento característico e intrínseco das espécies, com mais de 60% da variabilidade total atribuída às espécies. A herdabilidade da maioria das características avaliadas apresentou valores acima de 0,80, indicando que a maior proporção da variabilidade total é de natureza genética. Alta variabilidade genética, expressa pelo CVg, e detectada para as medidas de tempo, velocidade e sincronia foi registrada entre as matrizes de L. molleoides e C. fissilis. A magnitude dos valores de CVg mostrou que existe variação genética nas espécies estudadas com relação aos processos de germinação e emergência e, por se tratar de material com variabilidade natural, devem ser incluídas em projetos de conservação.<br>Mestre em Agronomia

Made available in DSpace on 2016-12-23T14:37:44Z (GMT). No. of bitstreams: 1 Joao_Vitor_Toledo.pdf: 607615 bytes, checksum: dab692118bf86f9eb81d6ef843ae5306 (MD5) Previous issue date: 2012-01-24<br>O eucalipto é a espécie florestal de rápido crescimento mais utilizada no Brasil, sendo o seu cultivo um dos mais avançados, produtivos e competitivos do mundo. O estresse induz mudanças e respostas em todos os níveis funcionais do organismo vegetal. O déficit hídrico, portanto, causa alterações no comportamento e desenvolvimento vegetal, e dependendo do genótipo, este pode ser mais ou menos tolerante a condições adversas do clima. Objetivou-se com este trabalho avaliar a influência de diferentes regimes hídricos em relação à água disponível no solo, sobre o crescimento e o desenvolvimento, durante 60 dias da fase de estabelecimento, de três clones de eucalipto, do híbrido Eucalyptus urophylla x Eucalyptus grandis. Este estudo foi desenvolvido em casa de vegetação instalada na área experimental do Centro de Ciências Agrárias da Universidade Federal do Espírito Santo, localizada no município de Alegre- ES. O experimento foi montado no esquema Fatorial 3x3 em delineamento experimental em blocos casualizados. Os tratamentos constituíram-se da interação de três níveis de água disponível no solo (50%, 30% e 10%), com o fator clones (Clone 1, Clone 2 e Clone 3), com quatro repetições. As mudas foram cultivadas em vasos com volume de 30 dm³. O controle dos níveis de depleção foi realizado através do monitoramento da massa de cada vaso, com o auxílio de uma balança, sendo a umidade elevada até a capacidade de campo até obter a umidade referente ao tratamento. Foram avaliados os valores de altura, diâmetro, número de folhas, área foliar, matéria seca total, matéria seca de folhas, matéria seca de raiz, matéria seca de haste e ramos, volume de raiz, lâmina total consumida e eficiência do uso da água. Os dados foram submetidos à análise de variância, e quando significativas, as médias foram comparadas pelo teste de Tukey ao nível de 5% de probabilidade. As avaliações executadas indicam que os níveis de disponibilidade de água abaixo de 50% da água disponível prejudicam o crescimento de todos os clones. A redução média da matéria seca total dos três clones estudados é de 21% e 40% para os níveis de 30% e 10%, respectivamente, em relação à produção de biomassa das plantas submetidas a 50% da água disponível. O Clone 2 apresenta médias estatisticamente superiores aos demais nos parâmetros matéria seca, número de folhas e eficiência do uso da água, se mostrando, portanto, superior sob condição de restrição hídrica. Portanto, o Clone 2 é mais indicado para implantação em regiões tanto com maior como menor disponibilidade hídrica<br>Eucalyptus is a fast growing tree species most used in Brazil, and its cultivation is of the most more advanced, productive and competitive in the world. Stress induces changes and responses in all functional levels the plant organism. The water deficit therefore causes changes in behavior and plant development, and depending on the genotype, it may be more or less tolerant to adverse weather conditions. The objective of this work was evaluate the influence of different regimes water through the water availability in the soil on the growth and development during 60 days of phase establishment of three eucalyptus clones, the hybrid Eucalyptus grandis x Eucalyptus urophylla. This study was conducted in a greenhouse attached to the experimental area of the Centro de Ciências Agrárias of Universidade Federal of Espírito Santo, located in municipality of Alegre-ES. The experiment was arranged with a 3x3 factorial arrangement in experimental randomized blocks design. The treatments consisted of interaction of three levels of available soil water (50%, 30% and 10%), with the clones factor (Clone 1, Clone 2 and Clone 3) with four replications. The seedlings were grown in vessels with a volume of 30 dm³. The control of the levels of depletion was performed by monitoring the mass of each vessel with the aid of a scale, being the humidity high up to capacity field until it obtains the moisture related to the treatment. It was evaluated values of height, diameter, leaf number, area leaf dry weight, dry leaves, root dry matter, dry stem and branches, root volume, depth and efficiency of the total consumed use of water. Data were analyzed by variance, and when significant, means were compared by Tukey test at level 5% probability. The evaluations performed indicate that the water availability levels below 50% of water available affect the growth of all clones. The average reduction of total dry matter of the three clones studied is 21% and 40% at levels of 30% and 10% respectively, for the production of biomass from plants subjected to 50% of available water. The Clone 2 presents averages statistically superior to the other in dry parameters, number of leaves and efficiency of water use, proving therefore more subject to water restriction. Therefore, the Clone 2 is more suitable for deployment in both regions more and less water availability

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior<br>CHAPTER II: Eugenia calycina is a fruit bearing species which is present in areas of the Savannah, whose fruit and seed morpho-physiological characteristics are rare. This being so, the objectives of the study were to quantify the influence of fruit coloration in the morphophysiological characters of fruit and seeds of the species; to determine pulp yield and to indicate the potential of the species for genetic improvement programs. In November 2006, fruits in green, orange, bright-red and dark-red colorations, 50 of each coloration were collected, their seeds extracted and both measured with relation to length and width, as well as fresh and dry weight pulp. In November 2007, from 20 matrixes, the number of fruits per plant and pulp yield was determined. The distribution for t Student was used to build confidential intervals for length, width and fresh and dry weight pulp and test the correlation coefficient between characters of the fruit and fresh weight pulp. Frequencies asymmetry and kurtosis measurements indicated the nature of the width and length distribution. Great ranges were observed in fruit size (8-20 mm width; 10-30 mm length) and seeds (8-14 mm width; 7-14 mm length), within the same maturation stage. The symmetrical and mesokurtic nature of the width and length distributions of the fruit and seeds reveal their genetic potential for selection, even with the anthropization of their area of occurrence. The production of fruit per plant was variable (3 to 20), with pulp yield estimated at 59.1%. CHAPTER III: The occurrence of fruit bearing species extensively cultivated in Brazil gives evidence to the need for a better knowledge of native flora and preservation of natural vegetable resources. The aimed was quantifying the influence of the coloration of Eugenia calycina Cambess. fruits in the emergency and development process of seedlings with the purpose of production of same. For the collection, green, orange, bright-red and dark-red coloring patterns of the fruit were established. These indicated the different maturation stages. The emergency experiment was installed in randomized block design, with four treatments (maturation stages) and seven repetitions of 28 seeds, totaling 28 parcels. To evaluate the seedling development, two independent experiments were installed both in randomized block design, using seedlings from the emergency test. In the first experiment, the treatments consisted of seedlings from the emergency test in different maturation stages (green, orange, bright-red and dark-red) and in the second, they consisted of a mixture of substrata containing commercial, vermicular and coconut peel substratum in different proportions. The fruit maturation stages did not affect the emergency process significantly, not even with regards to the increments in hypocotyls height, root length, stem diameter and number of leaves. The seedling emergence capacity was high (83.67 to 90.31%), however, on average, less than one seedling emerged per day (VE = 0.737 to 0.819 seedlings per day). Seedling growth was slow, maximum of 7 cm in 210 days, even when substratum was supplemented with chemical dressing (osmocote®), coconut peel and vermicular substratum.<br>CAPÍTULO II: Eugenia calycina é uma espécie frutífera de ocorrência em áreas de Cerrado, cujas características morfofisiológicas de frutos e sementes são escassas. Diante disso, os objetivos do trabalho foram quantificar a influência da coloração do fruto nos caracteres morfofisiológicos de frutos e sementes da espécie; determinar o rendimento de polpa e indicar o potencial da espécie para programas de melhoramento genético. Em novembro de 2006, cinqüenta frutos, na coloração verde, laranja, vermelho-claro e vermelhoescuro, foram coletados, extraídas suas sementes e ambos medidos quanto ao comprimento e largura, além das massas das matérias fresca e seca da polpa. Em novembro de 2007, de vinte matrizes, determinaram-se o número de frutos por planta e o rendimento de polpa. A distribuição t de Student foi utilizada para construir intervalos de confiança para comprimento, largura e massa das matérias fresca e seca de polpa, e testar o coeficiente de correlação entre caracteres do fruto e a massa fresca de polpa. Freqüências percentuais e medidas de assimetria e curtose indicaram a natureza da distribuição da largura e do comprimento. Grandes amplitudes foram observadas na morfometria dos frutos (8-20 mm de largura; 10-30 mm de comprimento) e das sementes (8-14 mm largura; 7-14 mm comprimento), dentro do mesmo estádio de maturação. A natureza simétrica e mesocúrtica das distribuições de largura e comprimento dos frutos e sementes revelam seu potencial genético para seleção, mesmo com a antropização de sua área de ocorrência. A produção de frutos por planta foi variável (3 a 20), com rendimento de polpa estimado em 59,1%. CAPITULO III: A ocorrência de espécies frutíferas amplamente cultivadas no Brasil evidencia a necessidade de melhor conhecimento da flora nativa e da preservação dos recursos vegetais naturais. Diante disso, objetivou-se quantificar a influência da coloração dos frutos de Eugenia calycina Cambess. no processo de emergência e no desenvolvimento de plântulas para fins de produção de mudas. Na coleta foram estabelecidos os padrões de coloração do fruto, verde, laranja, vermelho-claro e vermelho-escuro, indicando os diferentes estádios de maturação. O experimento de emergência foi instalado em delineamento de blocos casualizados, com quatro tratamentos (estádios de maturação) e sete repetições de 28 sementes, totalizando 28 parcelas. Para avaliar o desenvolvimento de plântulas, dois experimentos independentes foram instalados, ambos em delineamento de blocos casualizados, usando plântulas do teste de emergência. No primeiro, os tratamentos constaram de plântulas do teste de emergência em diferentes estádios de maturação (verde, laranja, vermelho-claro e vermelho-escuro) e, no segundo, constaram de mistura de substratos contendo substrato comercial, vermiculita e casca de coco em diferentes proporções. Os estádios de maturação dos frutos não afetaram significativamente o processo de emergência, nem mesmo os incrementos em altura do hipocótilo, comprimento de raiz, diâmetro do caule e número de folhas. A capacidade de emergência das plântulas foi alta (83,67 a 90,31%), porém, em média, menos de uma plântula emergiu por dia (VE = 0,737 a 0,819 plântulas por dia). O crescimento das plântulas foi lento, máximo de 7 cm em 210 dias, mesmo quando o substrato foi suplementado com adubação química (osmocote®), casca de coco e vermiculita.<br>Mestre em Agronomia

Les caracteristiques hydrodynamiques du sol jouent un role essentiel sur la repartition de l'eau en micro-irrigation, en particulier dans le cas d'une source ponctuelle. Il est donc important de pouvoir connaitre celles-ci facilement lorsqu'on s'interesse au dimensionnement et a la conduite des reseaux a la parcelle. La premiere partie de ce memoire presente une etude des principales methodes de caracterisation par infiltration axisymetrique qui sont actuellement en phase de developpement. Cette etude est effectuee a partir d'experimentations au champ et de la modelisation numerique et analytique des essais. Nous etudions les performances de ces methodes, et notamment l'influence de l'utilisation d'un regime permanent approximatif. Nous montrons, a partir d'une solution analytique transitoire, comment s'affranchir de l'hypothese d'un regime permanent pour ameliorer la precision des resultats de l'analyse multidisque. Nous etudions aussi la possibilite d'utiliser les instants initiaux des regimes transitoires, et l'effet de la variabilite spatiale a courte echelle. Dans la seconde partie de ce memoire nous presentons une solution quasi-analytique pseudo-transitoire pour l'infiltration sous une source ponctuelle (il n'existe pas de theorie analytique transitoire complete). Les parametres s'obtiennent par les methodes etudiees dans la premiere partie de ce memoire, sauf un parametre concernant la diffusivite capillaire. Cette solution approchee donne des resultats coherents avec les autres types de modelisation et les experimentations au laboratoire et au champ. Elle presente la particularite essentielle de representer les effets de la gravite sur la deformation du front d'humectation. Une version simplifiee, avec extractin racinaire, fournit un modele analytique pour les transferts d'eau sous un goutteur en micro-irrigation. Ce modele permet, dans certaines limites, d'etudier le dimensionnement et la conduite d'un reseau

Title page, table of contents and abstract only. The complete thesis in print form is available from the University of Adelaide Library.<br>Transient salinity in soils is characterised by high concentrations of salts in the subsoil. Durum wheat (Triticum turgidum L. Var. durum) is less tolerant of transient salinity than locally developed bread wheat (Triticum aestivum) varieties, and this results in reliable durum production being restricted to relatively unaffected soils. Field trials were conducted to assess the relative impact of transient salinity, boron toxicity and bicarbonate on crop production and highlighted the importance of combining tolerance to all three subsoil constraints into varieties intended for widespread adoption; and if the area of durum production is to be expanded. The Na exclusion locus from the landrace Na49 was found to improve the adaptation of durum to sites affected by transient salinity and is now being intogressed into a wide range of breeding material.<br>http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1152134<br>Thesis (Ph.D.) -- University of Adelaide, School of Agriculture and Wine, 2005

The experimental work reported in this thesis quantified the productivity of lucerne over a two-year period (2000-2001) for a Mediterranean climate at Roseworthy in South Australia (34°32′S, 138°45′E), and determined associated dynamics for water and nitrogen in duplex soil. Shoot growth of dryland lucerne was limited primarily by the pattern and amount of incident rainfall, but high temperature (30-35oC) also constrained summer production. These high summer temperatures induced greater production when irrigation was applied, but under the normally dry summer conditions high temperatures combined with soil water deficit (up to 200mm) caused growth to cease. Thus, shoot dry matter yield under rainfed conditions was 4.9 t ha⁻¹ in 2000 (from 7 harvests) and 1.8 t ha⁻¹ in 2001 (from 5 harvests) whereas summer irrigation increased yield to 14.9 t ha⁻¹ in 2000 (7 harvests) and 7.1 t ha⁻¹ in 2001 (5 harvests). Under rainfed conditions the RUE was 0.55 g DM MJ⁻¹ PARi compared with 1.08 g DM MJ⁻¹ PARi in the irrigated treatment in 2000, reducing to 0.4 g DM MJ⁻¹ for the rainfed and 0.7 g DM MJ⁻¹ under limited irrigation in 2001. Lucerne plant population declined from 69 to 20 (plants m⁻²) in the rainfed treatment and the plants partially compensated for this in 2000 by increasing stem density from 300 to 400 m⁻² in 2000 although this declined back to 300 m⁻² in 2001. In all treatments more than 70% of root biomass was in the top 40 cm soil, this was partially due to the vertical distribution of plant available water but also to subsoil constraints to root development below 0.6m. Nevertheless, lucerne was able to extract water and nitrate to 1800 mm soil depth. Large amounts of irrigation >400mm) over summer (Dec 1999-Mar 2000) increased total soil water content, approaching the drained upper limit; causing a 600% increase in shoot dry matter yield, similarly higher growth rate (71 kg DM d⁻¹) and higher RUE (~1.7 g DM MJ⁻¹ ), confirming that water availability was the main constraint to lucerne growth. Delayed benefits of summer irrigation, especially in the subsurface treatment, were also observed later (July to October) when lucerne was able to scavenge excess irrigation water and nitrate stored in the 600-1800 mm soil profile, which resulted in increased shoot growth. Drainage below the effective rooting depth was negligible, even under irrigation, confirming that lucerne can dry soil profiles and reduce deep drainage. Average annual water use efficiency was 9 kg DM ha⁻¹ mm⁻¹ under rainfed conditions compared to ~15 kg DM ha⁻¹ mm⁻¹ under irrigated conditions. Shoot dry mattter production was closely related to evapotranspiration in all treatments, however, under rainfed conditions losses from evaporation were proportionally higher compared to irrigated treatments. Sub-surface drip irrigation proved superior to surface irrigation using 22% less water compared to surface sprinkler irrigation treatment with comparable yields. Biological N₂fixation was strongly related to shoot production with 18 to 27 kg N fixed per tonne of shoot dry matter across all seasons and treatments. Dependence on N₂fixation appeared to be unrelated to soil mineral N concentration and amounts of nitrate in the profile (to 1m) were generally quite low <35 kg N ha⁻¹). Soil water dynamics under both rainfed and surface irrigated treatments were adequately simulated by the Agricultural Production System Simulator (APSIM) with RMSD < 10% of the observed means and R² > 0.80 for the total soil profile (0-2000 mm). Simulation of growth and development was less satisfactory. For example, the RMSD was ~50% of observed mean for shoot biomass (R² = 0.68) in the rainfed treatment, and 36% (R² = 0.77) in the irrigated treatment. Overall, simulation of shoot DM production was close to observed values during the growing season (Apr-Nov), however the model was unable to capture the observed shoot yield in response to summer irrigation, with simulated shoot DM 40% less than the observed value in 2000 and 35% less in 2001. N dynamics were poorly simulated under these soil and climate conditions. Amounts of soil mineral nitrogen (kg NO⁻₃-N ha⁻¹) were adequately simulated in rainfed conditions but consistently over-predicted under irrigated conditions. This evaluation of APSIM highlights both good and poor model performance and the analysis indicates the need for caution when applying the model in situations where observed data is scarce. Areas requiring improvements to the model are identified. Overall this research has improved understanding of the limitations to potential production of lucerne in a Mediterranean environment on duplex soils and shown that APSIM-Lucerne can be used confidently for many applications, particularly soil-water dynamics.<br>http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1352515<br>Thesis (Ph.D.) - University of Adelaide, School of Earth and Environmental Sciences, 2009

<p>Cover crop use, especially in no-till systems, is an evolving practice to maintain or improve soil health. There are many possible indicators of soil health, but this study focuses on the analysis of soil aggregate stability, soil active carbon, and soil organic matter. Soil aggregate stability is related to water infiltration and potential for soil erosion, while active carbon serves as an indicator of a readily-available food source for microbial activity, and soil organic matter serves as a mediator for the soil physical, chemical, and biological processes. The sites include: three Purdue Agricultural Centers, two soil and water conservation district sites, 12 farmer sites with conservation cropping systems, and seven conventional comparison sites. The treatments consisted of cover crop versus no cover crop use, or cover crop use with different tillage systems or nitrogen rates. In 2016 and 2017, soil samples were collected at a depth of 0-5 cm, air-dried, and separated into two soil size fractions: 0-2 mm and 2-8 mm. The wet sieve method was used to measure the mean weight diameter of the water stable soil aggregates from the 2-8 mm size fraction in both years. The potassium permanganate method was used to measure the soil active carbon from both size fractions in both years. The dry combustion method was used to measure the soil organic matter from both soil size fractions in 2017 only. Results showed relatively small improvements in soil active carbon and aggregate stability with the addition of three to four years of cover crops to the long-term no-till systems. However, these improvements were greater when comparing the cover crops plus no-till treatments to the conventional-till without cover crops. More work is needed to understand the dynamics of soil aggregate stability, soil active carbon, and soil organic matter in relation to soil health and cover crop use. Cover crops will likely have more impact on soil aggregate stability, active carbon, and organic matter with a longer duration of use.</p><p></p>