Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2017-05-02T14:34:44Z No. of bitstreams: 2 Tese - Luiz Henrique Xavier da Silva - 2017.pdf: 1441089 bytes, checksum: 55746a5600f86146bab348603732035a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2017-05-02T14:35:23Z (GMT) No. of bitstreams: 2 Tese - Luiz Henrique Xavier da Silva - 2017.pdf: 1441089 bytes, checksum: 55746a5600f86146bab348603732035a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) / Made available in DSpace on 2017-05-02T14:35:23Z (GMT). No. of bitstreams: 2 Tese - Luiz Henrique Xavier da Silva - 2017.pdf: 1441089 bytes, checksum: 55746a5600f86146bab348603732035a (MD5) license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Previous issue date: 2017-03-29 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The aim of this work was to evaluate dry matter yield (DMY), chemical composition and contribution of legumes in Brachiaria brizantha cv. Marandu pasture intercropped with a mixture of Stylosanthes spp. cultivars (Mineirão, Campo Grande and Bela) exposed to organic and conventional management during three years in two adjacent areas (Oxisol) with or without green manure (Crotalaria juncea). The experimental design was randomized blocks in split split plot with 3 repetitions and 3 factors: fertilizing, use of legumes and use of fungus. In the plot were made three types of soil fertilization management (no fertilization (Control), conventional management (CM) and organic management (OM) fertilization); in the split plot two planting management (with and without pigeon peas); in the spli split plot (with and without fungus). Three months before planting it was applied 2 t ha-1 of dolomitic limestone and 1 t ha-1 of gypsum and then green manure area was cropped using Crotalaria juncea to guarantee the organic Matter and N source. At planting OM was performed with N, K and P sources such as chicken manure (1.5%N), thermopotassium (6%K2O) and thermophosphate (12%P2O5) in amounts of 6.7 ha-1, 2 t ha-1 and 1 t ha-1, respectively. For CM treatment it was used potassium chloride (60%K2O), triple superphosphate (46%P2O5) and urea (46%N) totaling 200, 260 and 217 kg.ha-1, respectively. PMS did not present significant differences between the treatments studied. The organic management favored in both Brachiaria and Stylosanthes better chemical composition and nutritional quality. The multivariate analysis technique using the principal components analysis method was more efficient in the expressive determination of Brachiaria brizantha cv Marandu variables, with non - random behavior of the groups. / Objetivou-se com este trabalho avaliar a produção de matéria seca-PMS, composição químico e a contribuição da leguminosa em pastagens de Brachiaria brizantha cv. Marandu, consorciada com a mistura de cultivares de Stylosanthes spp (Mineirão, Campo Grande e Bela) manejados em sistema orgânico e convencional durante três anos, em duas áreas adjacentes (Latossolo) com e sem adubação verde (Crotalaria juncea). O delineamento experimental foi em blocos ao acaso, no esquema de parcela sub-subdividida, com 3 repetições e 3 fatores: adubação, uso de leguminosas e uso de micorriza. Na parcela, foram feitos três tipos de manejo de adubação do solo (convencional-MC, orgânico-MO e sem adubação-Testemunha); na subparcela, foram feitos dois manejos de plantio (sem e com guandu) e na sub-subparcela (com e sem micorriza). Três meses antes do plantio foi aplicado 2 t ha-1 de calcário dolomítico e 1 t ha-1de gesso. Em seguida na área com adubação verde a crotalária juncea foi cortada e incorporada ao solo para garantir fonte de matéria orgânica e N. Para o plantio no manejo orgânico foi realizada adubação com cama de frango (1,5% N), termopotássio (6% K2O) e termofosfato (12% P2O5) como fontes de N, K e P nas quantidades de 6,67 t ha-1, 2 t ha-1 e 1 t ha-1, respectivamente. No Manejo convencional foi realizada a adubação de plantio utilizando-se cloreto de potássio (60% K2O), superfosfato triplo (46% P2O5) e uréia (46% N), totalizando 200, 260 e 217 kg.ha-1, respectivamente. A PMS não apresentou diferenças significativas entre os tratamentos estudados. O manejo orgânico favoreceu em ambos Brachiaria e Stylosanthes melhor composição química e qualidade nutricional. A técnica de análise multivariada pelo método de análise de componentes principais mostrou ser mais eficaz na determinação expressiva das variáveis oriunda da Brachiaria brizantha cv Marandu, com comportamento não aleatório dos grupos.

O nitrogênio é o nutriente mineral essencial mais limitante ao crescimento das plantas. Apenas alguns microorganismos procariotos desenvolveram um mecanismo bioquímico que permite reduzir N2, abundante na atmosfera, a amônia, que pode ser assimilada pelas plantas. Muitos destes microorganismos conseguem associar-se simbioticamente com outros organismos, sendo a associação de bactérias do grupo Rhizobium com plantas do grupo das leguminosas a mais importante a nível econômico. Por outro lado, quando existe disponibilidade de nitrato no meio ambiente, a leguminosa abandona a fixação biológica absorvendo nitrato, que é reduzido a amônia pelas enzimas nitrato redutase (NR) e nitrito redutase (NiR) e, ao final, assimilada pelo sistema GS/GOGAT. Apesar de as duas vias terem amônia como produto final, em leguminosas tropicais, principalmente as pertencentes à tribo Phaseolae, quando a amônia provém de associação simbiótica a planta exporta, via xilema, preferencialmente ureídeos, enquanto quando a amônia provém da redução de nitrato, a planta exporta amidas, principalmente asparagina e glutamina. O objetivo do presente trabalho foi identificar, em Canavalia ensiformes (L.), as alterações metabólicas que ocorriam em função da concentração de nitrato fornecida à planta, através da quantificação localizada dos principais compostos nitrogenados do metabolismo de nitrogênio e dos principais sítios de redução de nitrato; bem como estudar o metabolismo de asparagina na leguminosa em questão desde o estádio de germinação até a fase reprodutiva, identificando os sítios preferenciais de metabolismo desta amida. Observou-se que o metabolismo de aminoácidos foi profundamente alterado em função da concentração de nitrato fornecida. Os níveis de aminoácidos solúveis totais não se alteraram drasticamente, o mesmo ocorrendo com os níveis de proteína e ureídeos, considerando-se os diferentes tratamentos em um mesmo estádio de desenvolvimento. Com a alteração do estádio de desenvolvimento, especialmente com o início da fase reprodutiva, o metabolismo de nitrogênio foi profundamente alterado, observando-se inversão no sítio de redução de nitrato, alterações nas concentrações totais de ureídeos e aminoácidos e alterações profundas no metabolismo de aminoácidos, quando se relaciona com o estádio vegetativo. A atividade de nitrato redutase, em Canavalia ensiformes (L.) mostrou-se regulada pela concentração de glutamina presente nos tecidos, tendo se mostrado mais elevada nos tecidos onde os níveis de glutamina eram menores. A alteração no sítio de redução de nitrato em função da mudança no estádio de desenvolvimento foi acompanhada pelo aumento simultâneo na concentração de glutamina solúvel nos tecidos onde a atividade da enzima foi menor. Em função das mudanças no estádio de desenvolvimento, percebeu-se também uma redução no número de sítios de possível atividade da enzima asparaginase, o que foi inferido pela redução no número de tecidos onde a enzima esteve presente, sugerindo então um possível aumento no catabolismo desta amida por ação da enzima asparagina-aminotransferase. Para maior entendimento dos processos que levam às alterações no metabolismo de nitrato, asparagina e aminoácidos de uma forma geral, os mecanismos de síntese e utilização de aminoácidos devem ser analisados para melhor compreensão dos processos envolvidos, através da análise da atividade das principais enzimas envolvidas nestes processos, bem como de estudos da transcrição dos respectivos genes. / Nitrogen is the most limiting essential nutrient for plant growth. Some prokaryotic microorganisms have developed a biochemical mechanism, which allows the reduction of N2, which is abundantly present in the atmosphere, to ammonium that can be assimilated by the plants. Many of these microorganisms form symbiotic associations with other organisms. This is especially true for leguminous plants that form symbiotic associations with bacteria belonging to the Bradyrhizbium, Rhizobium, and Sinorhizobium groups. Bacterial nitrogen fixation from these interactions are extremely important for the global nitrogen balance and plays a major economically role in agriculture. On the other hand, when nitrate is available in the environment, leguminous plants interrupt the symbiotic fixation process to directly use of the nitrate, which is reduced to ammonium by the enzymes nitrate reductase (NR) and nitrite reductase (NiR), and is finally assimilated by the GS/GOGAST system. Although both will result in ammonium as the end-product, in tropical leguminous plants species, mainly those of the Phaseoleae tribe, when ammonium is produced by the symbiotic association the plant translocates mainly ureides via xylem, whereas the plant translocate mainly amides such as asparagine and glutamine, when the ammonium is produced by nitrate reduction. The objective of this study was to identify in Canavalia ensiformes (L.), metabolic alterations dependent upon the concentration of nitrate supplied to the plant. Specific attention was given to the quantity of nitrogen compounds from nitrogen metabolism and asparagine metabolism from the early stage of germination to the reproductive stage, with the identification of the main locations of metabolism for this amide. Amino acids metabolism was significantly altered when nitrate was supplied at different concentrations. Total soluble amino acids, total protein and ureide contents were not dramatically altered when considering the different treatments at the same developmental stage. However, nitrogen metabolism was shown to be drastically altered when different development stages were compared, particularly at the beginning of the reproductive stage, at which time a switch in the location of nitrate reduction, alterations in the total concentration of ureides and amino acids were observed, when compared to the vegetative stage. Nitrate reductase activity of Canavalia ensiformes was shown to be regulated by the concentration of glutamine present in the tissues, exhibiting higher activity in tissues containing lower concentrations of glutamine, which coincided with the shift of the site of nitrate reduction with the changing developmental stage. The understanding of the processes leading to the alterations in the metabolism of nitrate, asparagine, amino acids, and the mechanism related to the synthesis and utilization of amino acids requires further studies.

Accroître la compétitivité des cultures vis-à-vis des adventices est un levier essentiel pour concevoir des systèmes de culture moins dépendants des herbicides. Les légumineuses sont des espèces majeures pour diversifier les systèmes mais elles sont réputées peu compétitives vis-à-vis des adventices. Cependant la variabilité entre espèces en particulier pendant la phase précoce a été peu explorée. Ce travail vise à i) étudier, via deux expérimentations en rhizotrons en serre, les traits impliqués dans la croissance et l’acquisition d’azote (N) en début de cycle chez une gamme d’espèces de légumineuse et les conséquences sur la compétition légumineuse-adventice et à ii) quantifier au champ l’intérêt d’associations légumineuse-non légumineuse (colzalégumineuses, maïs-légumineuses pérennes, la légumineuse étant plante de service) sur la croissance et la composition de la flore adventice. Nous montrons qu’il existe une variabilité entre espèces de capture d’N en début de cycle en lien avec les réserves azotées de la semence et l’exploration racinaire. La croissance et l’acquisition d’N de l’adventice sont impactées différemment selon l’espèce de légumineuse pendant la phase précoce. Les essais au champ montrent l’intérêt de combiner des espèces aux traits complémentaires pour l’utilisation des ressources conduisant à un meilleur contrôle des adventices tout en maintenant la productivité de la culture. Cette étude montre aussi que la composition de la flore est modifiée en fonction de la légumineuse insérée dans le système en lien à la fois avec les traits des légumineuses et les traits de réponse des adventices. / Enhancing crop competitiveness against weeds is a relevant way in order to design cropping system less dependent on herbicides. Legumes are key species in diversified cropping systems but they are known to be low competitive against weeds. However, inter-specific variability especially in the early growth had been little studied. Our work aims to i) study, via two greenhouse experiments in rhizotrons, the traits involved in the growth and nitrogen (N) acquisition for a range of legume species and the impacts on weed-legume competition at the beginning of crop cycle and to ii) quantify under field experiments the interest of legume-non legume intercropping (oilseed rapelegumes, maize-perennial legumes, where legume species were grown as service plant) on weed growth and weed species composition. Our results highlighted the inter-specific variability for soil N uptake in the early growth in relation with seed reserves and rooting exploration. Weed growth and N acquisition are influenced differently as a function of legume species in the early growth. Field experiments show the advantage of species combinations with complementary traits for using resources, leading to better weed control while maintaining crop productivity. This study shows also that weed species composition was modified as a function of legume species in relation with both legume traits and weed traits response.

Les endosymbioses racinaires sont des associations bénéfiques établies entre les racines des plantes et des micro-organismes du sol. Ces symbioses ont un intérêt agronomique et écologique puisque les plantes fournissent à leurs partenaires microbiens une niche écologique et des sucres issus de la photosynthèse et en retour, les micro-organismes associés aux racines vont fournir à la plante des nutriments minéraux qui sont actuellement apportés dans l’agriculture conventionnelle sous forme d’engrais. Durant ma thèse, j’ai particulièrement étudié la symbiose endomycorhizienne à arbuscules (AMS). Elle implique des champignons du groupe des Gloméromycètes et plus de 80 % des plantes terrestres. Ainsi cette symbiose est la plus répandue sur terre connue à l’heure actuelle. Plusieurs étapes importantes pour l’établissement de l’AMS ont été définies. La première de ces étapes est la reconnaissance mutuelle entre le champignon endomycorhizien et la plante hôte. Le champignon est capable de percevoir les plantes par les exsudats racinaires qu’elles sécrètent dans la rhizosphère. Dans le mélange complexe de molécules que sont les exsudats racinaires, des phytohormones appelées strigolactones activent le métabolisme des champignons endomycorhizien, la ramification des leurs hyphes et la production de molécules fongiques appelée facteurs Myc. La perception des facteurs Myc par la plante active des processus permettant la colonisation des racines par le champignon. Ce dialogue moléculaire entre champignons endomycorhiziens et plantes hôtes reste toutefois méconnu. Des molécules de type Lipo-chitooligosaccharides (LCO) ou chito-oligosaccharides (CO) ont été identifiées dans les exsudats de spores ou d’hyphes de champignons et activent la voie de signalisation symbiotique chez les plantes mais leurs rôles respectifs dans l’établissement de l’AMS restent mal compris. Du côté de la plante, des récepteurs potentiels aux LCOs et aux COs sont codés par les gènes de la famille des Lysin Motif Receptor-Like Kinase (LysM-RLK) qui sont capables de lier les constituants structuraux des LCOs et des COs. Cependant aucune preuve n’avait été apportée, au commencement de ma thèse, permettant de conclure sur le rôle des LCOs, des COs, et des LysM-RLKs dans la mise en place de l’AMS. C’est ce que je me suis attachée à démontrer durant ma thèse. Pour cela, j’ai travaillé sur une dicotylédone (la tomate : Solanum lycopersicum) et sur une monocotylédone (Brachypodium distachyon, un modèle pour le blé). Pour identifier les récepteurs aux LCOs dans ces plantes et déterminer leur rôle dans l’AMS nous avons mis en place des techniques de génétique inverse. Nous avons ensuite déterminé l’affinité de ces récepteurs pour les LCOs. Ainsi, nous avons montré que la perception des LCOs dans la tomate est importante pour la mise en place de l’AMS. Par ailleurs, je me suis intéressée à la symbiose entre des bactéries du type rhizobium et des plantes principalement de la famille des légumineuses. La mise en place de cette symbiose nécessite la synthèse de LCOs par les rhizobia et leur perception par la plante via des récepteurs de la famille des LysM-RLKs. Ces similarités que la symbiose rhizobium-légumineuses partage avec l’AMS nous ont conduits à poser la question de savoir si les récepteurs de LCOs impliqués dans l’AMS (beaucoup plus ancienne que la symbiose rhizobium-légumineuse) ont été recrutés durant l’évolution pour jouer un rôle dans la symbiose rhizobium-légumineuse. J’ai pu montrer que les récepteurs de LCOs impliqués dans l’AMS chez les espèces non-légumineuses susmentionnées sont fonctionnels l’établissement de la symbiose rhizobium-légumineuse chez une légumineuse. / Root endosymbioses are beneficial associations established between plant roots and soil microorganisms. These symbioses have an agronomic and ecological interest as plants provide their microbial partners with an ecological niche and carbohydrates from photosynthesis. In return, the root-associated microorganisms provide the plant with minerals that are currently being delivered in conventional agriculture as fertilizers. During my thesis, I particularly studied the arbuscular mycorrhizal symbiosis (AMS). It involves fungi of the Glomeromycota group and more than 80 % of land plants. This is the currently known most widespread symbiosis on earth. Important steps for the AMS establishment have been defined. The first step is the mutual recognition between the endomycorrhizal fungus and the host plant. Fungi can perceive plants through the root exudates. In the complex mixture of molecules in the root exudates, phytohormones called strigolactones activate the endomycorrhizal fungal metabolism, the branching of their hyphae and the production of fungal molecules called Myc-Factors. Myc-Factors are perceived by the plant and activate a signaling pathway allowing root colonization by the fungus. However, parts of the molecular dialogue between endomycorrhizal fungi and host plants remain unknown. Lipo-chitooligosaccharide (LCO) or chito-oligosaccharides (CO) molecules have been found in exudates of fungal spores or hyphae and were shown to activate the plant symbiotic signaling pathway, however their respective roles in the AMS establishment are unclear. Putative plant receptors for LCOs and COs are encoded by genes from the Lysin Motif Receptor-Like Kinase family (LysM-RLK) which are able of binding the structural LCO and CO components. However, at the beginning of my PhD, we had no evidence allowing to conclude about the involvement of LCOs, COs, or LysM-RLKs in the AMS establishment. During my thesis, I aimed to understand the role the LCOs and their plant receptors in AMS. For this, I used on a dicotyledon (the tomato: Solanum lycopersicum) and on a monocotyledon (Brachypodium distachyon that is a model for wheat). In order to identify the LCO receptors in these two species, I used a reverse genetic approach. Then I determined these receptors affinity for various LCO structures. I showed that in tomato, LCO perception is important for AMS establishment. In addition, I have studied the symbiosis between rhizobium-type bacteria and plants of the legume family. Interestingly, the establishment of this symbiosis requires LCO synthesis by rhizobia and LCO perception by the plant via receptors of the LysM-RLK family. The fact that rhizobium-legume symbiosis shares similarities with the AMS led us to ask whether the LCO receptors involved in AMS (a much more ancient symbiosis than the rhizobium-legume symbiosis) have been recruited during evolution for a role in the rhizobium-legume symbiosis. I demonstrated that the LysM-RLKs involved in AMS in the above mentioned non-legume species are functional for the rhizobium-legumes establishment in a legume species.

Goatsrue is an introduced perennial plant that has proven to have great invasive potential, leading to its classification as a noxious weed in many states and at the federal level. This research focused on seed biology, herbicide control, and toxic dynamics of goatsrue. Physical dormancy of mature goatsrue seed was tested through scarification using sulfuric acid with exposures of up to 60 minutes resulting in 100% germination. Comparison of dormancy for 26-year-old and 6-month-old goatsrue seed indicated aged seeds had reduced dormancy levels compared to newly harvested seeds, but had similar viability. Goatsrue seedling emergence was inversely related to burial depth; emergence was greatest at 0.5 cm soil depth (93%), and no emergence occurred from 12 and 14 cm. Goatsrue seed density ranged from 14,832 seeds m-2 to 74,609 seeds m-2 in the soil seed bank of five goatsrue-infested areas. Viability and dormancy of seeds recovered from the soil seed bank survey ranged from 91 to 100% and 80 to 93%, respectively. Goatsrue was most sensitive to the ALS inhibitor herbicides chlorsulfuron and imazapyr in greenhouse trials. Field studies showed that plots treated with dicamba, chlorsulfuron, metsulfuron, aminopyralid, triclopyr, and picloram provided at least 93% control of goatsrue 12 months after treatment at two field sites and increased perennial grass cover at one site. All treatments at one site decreased seedling goatsrue cover 11 months after treatment. The concentration and pools (dry weight x concentration) of the toxin galegine, found in goatsrue, vary over plant tissues and phenological growth stages. Galegine concentration is significantly different among plant tissues; reproductive tissues have the highest levels of galegine (7 mg/g), followed by leaf (4 mg/g), and then stem (1 mg/g) tissues. Galegine pools or the total amount of galegine per stalk was lowest at the vegetative growth stage and increased until reaching a maximum at the immature pod stage, but decreased nearly in half at the mature seed stage. Average galegine concentration also peaked at the immature pod stage and decreased by half at the mature seed stage. Thus, goatsrue is most toxic in its phenological development at the immature pod stage.

ABSTRACT Effects of Compost, Legume Cover Cropping and Vermicompost Extract Foliar Applications on Nutrition and Yield of Washington Navel Oranges William Payton Carling An experiment was conducted to test the effects of four treatments on Washington navel orange (Citrus sinensis) trees in regards to nutrient content of the leaves and fruit, soil nutrient content and properties, and fruit yield. The four treatments included: compost (C) and vermicompost extract foliar (VEF) applications, legume cover cropping (LCC) and VEF applications, VEF applications, and a control. The treatments were implemented from February 2010 to April 2011 and sampling occurred in May 2011. Fruit Growers Laboratory, Inc. (FGL) conducted the soil, leaf, and fruit analyses. The test site was located in San Isidro, Baja California Sur, Mexico. The compost used was made onsite with livestock manure, carbon-based farm waste, and water, and applied around the drip-lines of 8 WNO trees once every two months. The vermicompost and vermicompost extract was made onsite by introducing red wiggler worms (Eisenia fetida) into horse manure, allowing 1 month for casting content to build up, and collecting the extract as water was filtered through the material. Vermicompost extract was applied using a backpack foliar sprayer on 8 WNO trees twice a month. The legume cover crop treatment consisted of two plantings at a rate of approximately 72 seeds per square foot around the drip-lines of 8 WNO trees. Black-eyed peas (Vigna unguiclata) were planted in April 2010 and minimally incorporated using a hoe and shovel in August 2010. Fababeans (Vicia faba) and dry peas (Pisum sativum) were planted in January 2011 and minimally incorporated into the soil in March 2011. WNO leaf and soil analyses were compared to FGL optimum ranges. The C+VEF treatment showed trends of increased soil and leaf nitrogen, phosphorus, potassium, calcium, zinc, and copper levels and improved soil properties by raising soil organic matter percentage, saturation percentage, and moisture percentage. The control treatment had low or deficient values in these nutrients and soil properties. The LCC+VEF treatment increased nitrogen in the soil and leaf content but decreased organic matter percentage. The VEF treatment increased nitrogen and potassium content in the leaf but increased sodium beyond FGL optimum range. The C+VEF treatment had the highest yield and the greatest amount of nutrients removed as a result of yield. The C+VEF treatment had more available nutrients in the soil for WNO tree uptake and future crops.

Improved N management is required to enhance crop productivity, while reducing concomitant losses. Research was conducted for 4-y studying winter cover crops. Three legume species grown alone or with either cereal rye (Secale cereale) or ‘Tillage Radish®’ (Raphanus sativus L.) were used to quantify cover crop biomass and N content plus their effects on corn grain yield and N recovery. The effects of these cropping systems on selected soil health indicators was also determined. Rye bicultures enhanced biomass production, but antagonistically affected corn performance. Radish inclusion resulted in equal or greater cover crop N than rye. In year 3, the addition of radish across legume species increased corn N content (10.6 kg ha-1) and grain yield (1050 kg ha-1). Although cover crops did not affect soil bulk density, both bicultures increased soil C/N. The legume-radish association offers a novel practice towards improving crop performance and soil quality.

A 2-yr grazing study quantified pasture and animal responses of four forage systems (FS) grazed at two stocking rates (SR; 3 or 6 animals ha-1). Using „Marshall? annual ryegrass (Lolium multiflorum Lam.) and „Durana? white clover (Trifolium repens L.), FS treatments included spatially separated grass and legumes within the same paddock (SS), monoculture grass (MG), monoculture legume (ML), and a binary grass and legume mixture (MIX). Annual herbage mass (HM) was similar among FS at high SR (1900 kg ha-1), but at low SR, grass plots had greater HM (2900 vs. 2000 kg ha-1) than plots of legume monocultures. Animals on SS (1.12 kg) had greater average daily gain (ADG) than ML (0.97 kg), but neither was different from MG (1.08 kg) or MIX (1.00 kg). Low SR animals had greater ADG than high SR (1.09 vs. 0.99 kg). These results indicate that SS grazing system can improve pasture productivity.

Thesis (M.Sc. (Pasture Science)) -- University of Limpopo, 2022 / In South Africa, livestock production is a rapidly growing business in the agricultural sector contributing up to 46.9% of the gross domestic value. The shortage of adequate, good quality forage during the winter months is one of the biggest problems confronting livestock farmers in the Limpopo Province. This study was initiated in 2019 to evaluate the production potential and nutritive value of different summer annual forage legumes, namely sunnhemp (Crotalaria juncea), forage cowpea (Vigna unguiculata), lablab bean (Lablab purpureus), and pigeon pea (Cajanus cajans), and their impact on succeeding winter stooling ryegrass (Secale cereale), at the University of Limpopo experimental farm Syferkuil and a Cooperative farmers’ field at Ofcolaco. The study was evaluated in a randomized complete block design with four replications. Dry matter yield, crude protein, crude protein yield, leaf chlorophyll content, Normalized Difference Vegetative Index (NDVI), and leaf gaseous exchange parameters of forage crops were statistically analysed with Statistical Analysis System (SAS), Enterprise Version 9.4, using the least significant difference (LSD) method for mean comparison. Pigeon pea biomass accumulation was 57% lower than the average of the three other legumes at Syferkuil. Sunnhemp produced superior biomass (P<0.05) compared to the other three species, reaching a peak yield of 3142.4 kg.ha-1 and 8970.8 kg ha-1 at Syferkuil and Ofcolaco, respectively. Cowpea and lablab produced similar biomass at Syferkuil. The crude protein content of the forage species ranged from 22.91% to 26.82% at Syferkuil and 17.03% to 23.84% at Ofcolaco. Leaf chlorophyll content differed (P<0.001) among the forage legume species at both locations with cowpea producing the highest chlorophyll content at Syferkuil, whereas at Ofcolaco, pigeon pea constantly produced the highest chlorophyll compared to other species. Pigeon pea was the only species rated moderately healthy with Normalised Difference Vegetative Index (NDVI) readings at Syferkuil, unlike at Ofcolaco where all forage legumes were rated as very healthy. At Syferkuil, no root nodules were observed among all the forage legumes at all sampling dates but at Ofcolaco, nodules were produced at 44 DAE with cowpea producing the highest, 92.32% higher than the average of sunnhemp, lablab, and pigeon-pea. At this location pigeon pea did not nodulate. The transpiration rate at Syferkuil was significant (P<0.01) among the species starting with a low transpiration rate from 24 days after planting and reaching their peak at 66DAE. Overall, pigeon pea had the highest (P<0.05) mean transpiration rate compared to the other species. At Ofcolaco the forage legume treatment did not have any significant (P>0.05) influence on transpiration rate, stomatal conductance and sub-stomatal conductance. The transpiration rate of the species ranged from 0.1 mol m-2 s -1 to 5.15 mol m-2 s -1 across all sampling dates whereas stomatal conductance ranged from 0.06 to 5.59 mol m-2 s -1 at Syferkuil and 0.1 to 5.15 mol m-2 s -1 at Ofcolaco, across all sampling dates and species. At Syferkuil, the mean stomatal conductance values ranged from 129.75 mol m-2 s -1 to 374 mol m-2 s -1 across the sampling dates and species, whereas, at Ofcolaco, the means ranged from 185 mol m-2s -1 to 390.25 mol m-2s -1 . The succeeding stooling rye produced a similar biomass yield under every preceding forage legume. This can be concluded that all the four forage legumes did not have any effect on the biomass production of stooling rye. However, there appeared to be a tendency of higher biomass production in the grass species grown after pigeon pea and lablab compared to those following sunnhemp and cowpea. Further experiments are required to establish the full benefits of the forage legumes on succeeding forage grass crop. Based on the results from this study, it was concluded that sunnhemp can be considered as the first choice forage legume at both Syferkuil and Ofcolaco due to its consistently high biomass production, comparable nutrient profile, high crude protein content and high protein yield compared with the other legumes. Though sunnhemp was superior, the other forage summer legumes species studied also managed to produce enough biomass for grazing and had similar nutritive value which was above minimum recommendations. They can therefore be cultivated in the province to meet the constraint of the feed gap in the province. Additional studies at different locations, however, will help to understand the productivity of the species and also to establish the full benefits of the forage legumes on succeeding forage grass crops / National Research Foundation (NRF) and Department of Science and Innovation

Nitrogen (N) fertilizer application constitutes a major portion of farmers' cost of production since N is the most applied nutrient in U.S. cotton production. Despite this, N uptake and use efficiency (NUE) in cotton remains below 50%, which presents challenges of environmental quality. Studies were conducted across 4 states in the US Cotton Belt with the overall objective of evaluating strategies to reduce loss of N to the environment, increase N uptake and NUE. The first study had two objectives: 1) compare NH3 volatilization from surface versus subsurface application/placement of granular (urea) and fluid N source (urea ammonium nitrate; UAN32); and 2) compare NH3 volatilization from urea and UAN treated with enhanced-efficiency fertilizer products. For this study, four A horizon soils of different types were collected from four sites in Virginia (VA), Georgia (GA), Tennessee (TN), and Texas (TX). The EEF products were N-(n-butyl) thiophosphoric triamide (NBPT), nitrapyrin, and ESN. In the first set of experiments (N placement experiments), it was found that across soil types, subsurface placement of granular N source reduced NH3 volatilization by 58 – 81% and subsurface placement of UAN reduced NH3 volatilization by 56 – 98%. In the second set of experiments (EEF experiments), it was found that NBPT reduced NH3 volatilization by 5 – 77% across soil types, and the highest reduction in losses by NBPT was observed on sandier and low CEC soils. Treating urea with both nitrapyrin and NBPT was more effective at reducing NH3 volatilization compared to treating urea with nitrapyrin alone. Based on our findings, subsurface application of granular and fluid N sources is recommended as strategy to reduce NH3 volatilization. Where subsurface placement is not possible, EEF products should be considered. The objectives of the second study were: 1) determine the effects of small grain and legume cover crops on N cycling; 2) evaluate the effects of cover crops and N fertilization on N uptake; and 3) evaluate the effects of cover crops on lint yield. Cover crops were winter fallow (winter weeds), small grain [cereal rye (Secale cereale)], legume mix [(50% crimson clover (Trifolium incarnatum): 50% hairy vetch (Vicia villosa)], and legume mix + rye [(67% legume mix:33% hairy vetch)]. Fertilizer N application rates were 0, 45, 90, and 135 kg ha-1. Soil inorganic N in the top 30 cm depths of the legume mix and legume mix + rye plots was consistently higher than in the rye lone or fallow plots. Cotton lint yield following legume mix with 45 kg ha-1 fertilizer N application was comparable to following fallow plots with 135 kg N ha-1. Thus, fertilizer N rate could considerably be reduced when cotton follows legume cover crops. The objectives of the third study were: 1) evaluate urea and UAN placement (broadcast, dribbling, and injection) on lint yield and fiber quality of three cotton maturity groups (early-, mid-, and full-maturity); (2) assess N use and agronomic efficiencies as influenced by N source, rate, and placement; (3) evaluate the impact of N source and placement on fiber quality. A study including 9 site-years studies was conducted in VA, GA, and TX. It was found that placement had no effect on yield in VA, had effect in all 3 years in TX, and had effect in 1 year in GA. Yield responded to N application in 8 out of 9 site-years in this study. Nitrogen use efficiency was highest among the early- and mid-season varieties. Overall, N rate and variety, rather than application/placement strategy, had the most pronounced effects on lint yield. / Doctor of Philosophy / Nitrogen (N) is usually the major limiting nutrient in cotton production and represents a significant cost of production. On average, the current proportion of applied N recovered in the aboveground crop biomass, (i.e., nitrogen use efficiency, or NUE) ranges from 33 – 50%, meaning that up to two-thirds of applied N is not recovered by crops. This unrecovered N not only represents economic loss to growers, but acts as a potential pollutant in the environment. There is a need for practices which increase N uptake in cotton production, agronomic efficiency, and environmental sustainability. Previous studies conducted outside the U.S. Cotton Belt reported that NUE is influenced by N source and rate of application. Data on NUE of contemporary cotton varieties utilized in the humid and semi-arid regions of the U.S. Cotton Belt would prove useful in efficient N management in the region. First study evaluated gaseous N loss from fertilizer application. It was found that subsurface placement of granular urea reduced NH3 loss as much as 58 – 81% compared to surface broadcast granular urea and subsurface placement of fluid N source reduced NH3 loss by 56 – 98%. In a second study, N rate and method of application/placement were evaluated. Here, it was found that N rate and cotton variety, rather than application/placement strategy had a more pronounced effect on cotton yield. Lastly, the potential of cover crops as alternate N source in cotton production was investigated. It was found that cotton yield following legume mix and fertilized with 45 kg of N per hectare was comparable with cotton yield following no cover crop and fertilized with 135 kg of N per hectare. The results of these studies indicate that subsurface placement of granular and fluid N sources can reduce NH3 loss. In addition, all other things being equal, choosing the right cotton variety as well as applying the right N rate are critical for yield. Furthermore, by growing cotton after legume cover crops, N fertilizer application rates can be significantly reduced.