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Among the several essential nutrients in the nutrition of the maize, without a doubt, the nitrogen (N) is one of the most important. However, most of the time, the amount naturally available in the soil is insufficient to supply the demand for N, turning the complementation with nitrogen fertilization to maize essential for obtaining of expressive yields, besides to represent a significant part of the production costs. In that way, the rational use of nitrogen fertilization associated to the best use of the N released by residues cultural predecessors is an aspect of extreme importance for the maize production inside of scenery economically viable and correct ecologically. The main objective of this work was to study the N availability dynamics in the soil influenced by residues from cover crops predecessors and to evaluate the use of new technologies to nitrogen fertilizer management in the maize in no-tillage system (NT). For that, specifics and supplementary studies were carried out, looking to evaluate the residues decomposition dynamics and N release (Chapter I); the soil N availability effects (Chapter II); the N absorption until flower stage and maize yield in function of the amount of residues added by different combination of cover crops and N fertilizer levels in NT (Chapter III). Also the N fertilizer value was evaluated from hairy vetch residues to maize using 15N-isotope techniques (Chapter IV) and the comparative use of soil and plants parameters to N fertilizer variable rate recommendation in the maize, looking to increase the efficiency of the N applied (Chapter V). The rates of decomposition were not significantly influenced by amounts of residues added in the soil, but the N mineralization and immobilization processes were intensified. Already the addition and residues decomposition dynamics influenced directly the mineral N availability in the soil when not compared to the addition of residues. The influence in the N availability dynamics in function of the addition of residues was evident in the results of N accumulation until flower stage and in the transformation of this N accumulated in yield grains. The results showed that maize yield was directly proportional to N absorption and that maize sowed in succession hairy vetch presented larger production capacity in relation to black oat and oil radish residues, even with N fertilizer supplementary. The yields upper to 9 Mg grains ha-1 only was possible with accumulated upper to 150 kg N ha-1 until flower stage, and only in the succession hairy vetch/maize was possible to reach such amount. However, in spite of the recognized capacity to N supply of the hairy vetch residues, associated the biologic nitrogen fixation capacity this cover crop and higher N addition to soil, the N maximum recovery was 27% the first year and 5% in the second year. Like this, it is concluded that the maize N recovery after hairy vetch is lower to be totally responsible for the yield increase, suggesting that the hairy vetch may have a positive effect besides of the N supply. The group of results suggests that the higher N availability in the initial phase of the maize development provided by fast hairy vetch decomposition is an essential factor in the increase of the yield usually observed in the succession hairy vetch/maize. Verified still the parameters of plants presented the best performance in the diagnosis of the demand of N for the maize in relation to the soil parameters, improving the synchronization between availability and demand, spatially variable during the maize development. / Entre os vários nutrientes essenciais na nutrição do milho, sem dúvida, o nitrogênio (N) é um dos mais importantes. No entanto, na maioria das vezes, a quantidade naturalmente disponível no solo é insuficiente para suprir a demanda por N, tornando a complementação com fertilizante nitrogenado no milho fundamental para obtenção de expressivas produtividades, além de representar uma parcela significativa dos custos de produção. Dessa forma, o uso racional de fertilizantes nitrogenados associado ao melhor aproveitamento do N liberado pelos resíduos culturais antecessores é um aspecto de extrema importância para a produção de milho dentro de um cenário agrícola que busca sustentabilidade econômica e que seja ecologicamente correto. Este trabalho teve como objetivo principal estudar a dinâmica de disponibilidade de N no solo influenciado pelo aporte de resíduos de culturas de cobertura antecessoras e avaliar o uso de novas tecnologias no manejo da adubação nitrogenada no milho em sistema plantio direto (SPD). Para tanto, estudos específicos e complementares foram conduzidos, buscando avaliar a dinâmica de decomposição de resíduos e liberação de N (Capítulo I); os efeitos sobre a disponibilidade de N no solo (Capítulo II); a absorção de N no florescimento e a produtividade milho em função da quantidade de resíduos aportados por diferentes culturas de cobertura, combinadas com doses de N em SPD (Capítulo III). Também se avaliou o valor fertilizante do N oriundo dos resíduos de ervilhaca através de técnicas isotópicas com 15N (Capítulo IV) e o uso comparativo de parâmetros de solo e planta na recomendação da adubação nitrogenada a taxa variável no milho, buscando aumentar a eficiência do N aplicado (Capítulo V). As quantidades de resíduos adicionadas ao solo não influenciaram significativamente as taxas de decomposição, mas intensificaram os processos mineralização e imobilização de N. Já o aporte e a dinâmica de decomposição dos resíduos influenciaram diretamente a disponibilidade de N mineral no solo, quando comparado ao não aporte de resíduos. A influência na dinâmica de disponibilidade de N em função de aporte de resíduos ficou evidente nos resultados de acúmulo de N até o florescimento e na transformação deste N absorvido em produtividade de grãos. Os resultados obtidos mostraram que a produtividade milho foi diretamente proporcional à absorção de N e que o milho semeado em sucessão à ervilhaca apresentou maior capacidade produtiva em relação aos resíduos de aveia preta e nabo forrageiro, mesmo com adubação nitrogenada complementar. Produtividades de milho superiores a 9 Mg ha-1 de grãos somente foram possíveis com o acúmulo superior a 150 kg ha-1 de N até o florescimento, sendo que somente na sucessão ervilhaca/milho foi possível alcançar tal quantidade. Porém, apesar da reconhecida capacidade de fornecimento de N pelos resíduos de ervilhaca, associado à capacidade de fixação biológica desta cultura e do elevado aporte de N ao solo, a recuperação de N máxima obtida foi de 27% no primeiro ano e 5% no segundo ano. Assim, concluiu-se que a recuperação de N pelo milho após ervilhaca é baixa para ser totalmente responsável pelo aumento de produtividade, sugerindo que a ervilhaca possa ter efeitos positivos ao milho além do fornecimento de N. O conjunto de resultados sugere que a elevada disponibilidade de N na fase inicial de desenvolvimento do milho proporcionada pela rápida decomposição dos resíduos de ervilhaca, seja um fator essencial no aumento da produtividade normalmente observada na sucessão ervilhaca/milho. Verificou-se ainda que os parâmetros de plantas apresentaram o melhor desempenho no diagnóstico da demanda de N pelo milho em relação aos parâmetros de solo, melhorando o sincronismo entre disponibilidade e demanda, espacialmente variável durante o desenvolvimento do milho.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The no-tillage system (SPD) was one of the main innovations in Brazilian agriculture, but there are still discussions about how to achieve and maintain its quality and sustainability. The management of SPD areas through management zones presents great potential for this purpose, since it integrates different variables in order to facilitate and increase the technical and computerized management of agricultural practices and consequently the reduction of polluting potencies in environments. Among the main variables used to delimit management zones are the chemical attributes, yield maps and recently the NDVI index. In this sense, with Article I, the objective was to delimit management zones through yield maps and NDVIs derived from satellite images in historical series. To do this, in an area of 118 ha, three yield maps of different cultures between the years of 2010 to 2015 were selected and for each yield map we searched for the images from the Landsat 5 and 8 satellite that included a date in of the cycle of the crop in question from which the NDVI was calculated and also with the intention of verifying the stability of the NDVI generated in different crop cycles, four other satellite images were selected for four crops according to the historical of the study area, between the years 2007 and 2013. In article II, the objective was to verify the variability caused by the winter cover crop in the summer crop and if the NDVI index performed by land and with a RPAS is able to evidence this variability in the summer crop. In an area 73.96 there was applied a sampling grid of 70.71 x 70.71 m (0.5 ha), where soil sampling for chemical analysis and dry matter nutrients accumulated in the winter cover crop of black oats where soybean was sown in the summer, in which in the R5 and R5.5 stages evaluations were carried out with a portable sensor "by land" and with a RPAS for obtaining of the NDVI index and finally the grain yield of the soybean was determined, as well as the final population of plants. With the results, NDVI from satellite images can replace and/or compose the yield maps (article I) and that the dry mass and accumulated nutrients in the winter crop interfere with the yield of the summer crop and the NDVI index performed by land or with a RPAS was effective in expressing this variability (article II). / O Sistema Plantio Direto (SPD) foi uma das principais inovações na agricultura brasileira, contudo ainda há discussões sobre como alcançar e manter sua qualidade e sustentabilidade. A gestão de áreas sob SPD por meio de zonas de manejo, apresenta grande potencial para essa finalidade, pois integra diferentes variáveis afim de facilitar e incrementar a gestão tecnificada e informatizada das práticas agrícolas, e em consequência a redução de potencias poluidores no ambiente. Entre as principais variáveis utilizadas para delimitar zonas de manejo estão os atributos químicos, mapas de rendimento e recentemente o índice NDVI. Nesse sentido, com o artigo I objetivou-se delimitar zonas de manejo por meio de mapas de rendimento e NDVI oriundos de imagens de satélite em series históricas. Para isso, em uma área de 118 ha, selecionou-se três mapas de rendimento de diferentes culturas compreendidas entre os anos de 2010 a 2015 e para cada mapa de rendimento buscou-se selecionar as imagens satélite oriundas série Landsat que compreendessem uma data dentro do ciclo da cultura em questão a partir das quais procedeu-se o cálculo do NDVI e ainda com o intuito de verificar a estabilidade do NDVI gerado em diferentes ciclos de cultivo, foram selecionadas outras quatro imagens de satélites referentes a quatro cultivos, segundo o histórico de cultivo da área de estudo, compreendidos entre os anos de 2007 a 2013. Já no artigo II, o objetivo foi verificar a variabilidade causada pela cultura de cobertura de inverno na cultura de verão e se o índice de NDVI realizado “por terra” e com um RPAS é capaz de evidenciar essa variabilidade na cultura de verão. Em uma área 73,96 ha, aplicou-se uma malha amostral de 70,71 x 70,71 m (0,5 ha), onde realizou-se a amostragem de solo para a análise química e as avaliações de matéria seca e os nutrientes acumulados na cultura de cobertura inverno da aveia preta onde sobre esta, foi semeada no verão a cultura da soja, na qual nos estágios R5 e R5.5 foram realizadas avaliações com um sensor portátil “por terra” e com um RPAS para a obtenção do índice de NDVI e por final determinou-se o rendimento de grãos da soja, bem como, a população final de plantas. Com os resultados, constatou-se que O NDVI foi um bom parâmetro para delimitar duas zonas de manejo de alto e baixo potencial (artigo I) e que a matéria seca e os nutrientes acumulados na cultura de inverno interferem o rendimento da cultura de verão, sendo que o índice de NDVI realizado “por terra” ou com um RPAS foi eficaz em expressar essa variabilidade (artigo II).

O Greening ou Huanglongbing (HLB) é a doença mais devastadora dos citros na atualidade. Levantamentos mostram que a enfermidade está presente em cerca de 60% dos talhões do parque citrícola paulista, demostrando sua grande capacidade de disseminação. O psilídeo-asiático-dos-citros, Diaphorina citri Kuwayama (Hemiptera: Psylidae) é um importante vetor dos agentes causais associados ao HLB. Sua capacidade de dispersão está intimamente relacionada ao progresso da doença no campo. Não se tem conhecimento dos principais fatores que possam interferir no deslocamento do inseto até plantas cítricas. Sendo assim, a presente pesquisa teve como objetivo investigar a influência de alguns fatores ambientais sobre a dispersão do psilídeo D. citri, discutindo-os em relação à epidemiologia do HLB dos citros. Inicialmente foram realizados testes em laboratório para adaptação da metodologia de marcação, liberação e recaptura usando pó fluorescente. Grupos de psilídeos adultos foram marcados e sua sobrevivência avaliada, verificando a influência de quatro cores distintas de pó fluorescente (amarelo, azul, rosa e verde). Posteriormente realizaram-se estudos de campo com quatro liberações de psilídeos, com marcadores distintos, em quatro áreas experimentais circulares e adjacentes, sendo formadas por círculos concêntricos localizados a 18, 24 e 30 m de cada centro de liberação. Os insetos foram monitorados visualmente e por armadilhas adesivas amarelas. Nas 1ª e 2ª liberações, foi verificado o efeito das coberturas vegetais milho (Zea mays L.) e capim-braquiária (Brachiaria decumbens Stapf.) na dispersão de D. citri. Já nas 3ª e 4ª liberações, foi estudado o efeito de brotações no deslocamento do inseto. A influência dos ventos foi avaliada em ambas as situações. A análise de sobrevivência indicou que não houve interferência das quatro cores de pó fluorescente em D. citri, sendo a marcação visível no corpo dos insetos durante os 48 dias de avaliação. De acordo com as análises fatoriais, não foi observada qualquer interferência da cobertura vegetal milho, medindo 2 m de altura, na dispersão do inseto. Na presença de brotações, adultos de D. citri dispersaram menos em busca de novos hospedeiros, acumulando-se nas primeiras linhas de plantas cítricas. Após 6 horas da liberação, a capacidade de dispersão máxima de D. citri foi três vezes maior na condição de ausência de brotações. A dispersão média e a área total abrangida variaram assimptoticamente com o tempo, ou seja, o inseto possui inicialmente grande velocidade de dispersão, porém esta tende a se estabilizar com o incremento do tempo. Esses resultados deixam claro que D. citri realiza movimentos dependendo das condições fenológicas de seus hospedeiros, ressaltando a grande importância de se intensificar métodos de controle regionais em épocas em que o fluxo vegetativo das plantas cítricas não é tão intenso. / Greening or Huanglongbing (HLB) is the most devastating disease of citrus today. Surveys show that the disease is present in about 60% of the park stands citrus Sao Paulo, demonstrating its great ability to spread. The Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psylidae) is an important vector of the causative agents associated with HLB. Its ability to spread is closely related to disease progression in the field. There is no knowledge of the main factors that can affect the movement of the insect to citrus plants. Thus, the present study aimed to investigate the influence of some environmental factors on the dispersal of psyllid D. citri, discussing them in relation to the epidemiology of HLB of citrus. Initially tests were performed in the laboratory to adapt the methodology of marking, release and recapture using fluorescent powder. Groups of adult psyllids were marked and their survival assessed by checking the influence of four different colors of fluorescent powder (yellow, blue, pink and green). Subsequent studies were conducted with four field releases psyllids, with distinct markers on four experimental areas adjacent circular and being formed by concentric circles located at 18, 24 and 30 m for each center release. The insects were monitored visually and by yellow sticky traps. In the 1st and 2nd releases, was to determine the effect of cover crops maize (Zea mays L.) and grass (Brachiaria decumbens Stapf.) in the dispersal of D. citri. In the 3rd and 4th releases, were studied the effect of shootings in insect movement. The influence of the wind has been evaluated in both situations. Survival analysis indicated that there was no interference of the four colors of fluorescent powder on D. citri, and marking was visible on the body of insects during the 48 days of evaluation. According to the factor analysis, no interference of vegetation corn (measuring 2 m in height) was observed in the dispersal of the insect. In the presence of shoots, adult D. citri less dispersed looking for new hosts and it accumulate in the first lines of citrus plants. After 6 hours of release, the D. citri maximum dispersal was three times higher in the condition of absence of shoots. The dispersal medium and the total area covered varied asymptotically with time, ie the insect has initially high speed dispersal, but this tends to stabilize with increasing time. These results clearly show that D. citri performs movements depending on the phenology of its hosts, emphasizing the importance of intensifying regional control methods at times when the flow of plant citrus is not intense.

Made available in DSpace on 2014-07-29T14:52:06Z (GMT). No. of bitstreams: 1 Tese Jeander Oliveira Caetano.pdf: 1156626 bytes, checksum: c57accce2f7f7f942e8b9d04e2aba986 (MD5) Previous issue date: 2011-02-25 / Crop rotation and the increase in straw on the soil are among the main requirements for the implementation and maintenance of no-tillage in the Cerrado. The use of integrated crop and livestock production, coupled with the introduction of Brachiaria in agricultural areas has helped to maintain this coverage and increased amounts of plant species as alternatives to rotation. Thus, there is a need to evaluate these cover crops and forms of fertility management which are widely used by farmers in Brazil. The aim was to evaluate the effect of two forms of soil correction, four types of soil cover and four levels of KCl on production and nutrient content of aerial part dry biomass of soil cover types, the yield and content soybean leaf nutrient and chemical attributes of an Oxisol. The experimental was arranged in a randomized block design, with four replications, the field was laid out in 2x4x4 and arranged in strip-split plot design. Was evaluated the forms of soil correction initial total and annual installment (main plot), the types of soil cover Brachiaria brizantha, B. ruziziensis, sorghum crop residues and spontaneous vegetation (subplots) and the levels of KCl correspondents to 0 kg ha-1, 20 kg ha-1, 40 kg ha-1 e 60 kg ha-1 of K2O (subsubplots). On the soil, for the depths 0-20 cm and 20-40 cm analyzed the pH CaCl2, organic matter, exchangeable Ca, Mg, K and Al, H+Al and the contents of available P, Fe, Mn, Cu and Zn. In the leaves were determined N, P, K, Ca, Mg, Fe, Mn, Cu and Zn. Was collected dry biomass of soil cover and estimated soybean yield. The forms of soil correction initial total and annual installment not influence soybean yield. B. brizantha produces highest biomass, which occurs in the highest soybean yield. Potassium is the nutrient of greatest accumulation in leaf of B. brizantha and B. ruziziensis. The increasing levels of KCl do not affect the soybean yield. The soybean yield is more affected by the kind of cover crops than by the form of correction and levels of potassium. / A rotação de culturas, aliada à elevação de palhada sobre o solo, estão entre os principais requisitos para a implantação e manutenção do sistema plantio direto no Cerrado. O uso da integração lavoura-pecuária, aliada à introdução das braquiárias em áreas agrícolas, tem auxiliado a manutenção dessa cobertura e o aumento da quantidade de espécies de plantas como alternativas para rotação. Assim, ocorre a necessidade da avaliação dessas plantas de cobertura e das formas de manejo da fertilidade que são amplamente utilizadas pelos agricultores no Brasil. O objetivo foi avaliar o efeito de duas formas de correções de solo, quatro tipos de cobertura vegetal e quatro doses de KCl sobre a produção e teor de nutrientes da parte aérea da biomassa seca dos tipos de cobertura vegetal, a produtividade de grãos e teor de nutrientes foliares da soja e os atributos químicos de um Latossolo Vermelho. O delineamento foi em blocos ao acaso, com quatro repetições, em parcelas subsubdivididas 2x4x4. Foi avaliada as formas de correção de solo total inicial e parcelada anual (parcela), os tipos de cobertura vegetal do solo Brachiaria brizantha, B. ruziziensis, restos culturais de sorgo e vegetação espontânea (subparcela) e as doses de KCl correspondentes a 0 kg ha-1, 20 kg ha-1, 40 kg ha-1 e 60 kg ha-1 de K2O (subsubparcela). No solo, para as camadas de 0-20 cm e de 20-40 cm, analisaram-se o pH CaCl2; a matéria orgânica; os teores de Ca, Mg, K e Al trocáveis; o H+Al e os teores disponíveis de P, Fe, Mn, Cu e Zn. Nas folhas analisaram-se N, P, K, Ca, Mg, Fe, Mn, Cu e Zn. Realizou-se a coleta da biomassa seca das coberturas e dos grãos da soja. As formas de correção total inicial e parcelada anual não influenciam o rendimento da soja. A B. brizantha produz a maior biomassa seca, sob a qual ocorre o maior rendimento de soja. O potássio é o nutriente de maior acúmulo foliar na B. brizantha e B. ruziziensis. A elevação das doses de KCl não tem influência sobre o rendimento da soja. O rendimento de grãos de soja é mais afetado pelo tipo de cobertura do solo do que pela forma de correção e dose de potássio.

Low cover crop biomass production is a major obstacle to the success of conservation agriculture currently promoted as panacea to the inherent problem of soil erosion and loss of soil productivity in the Eastern Cape (EC). Therefore, this study evaluated cover crop management strategies for optimizing biomass production for better soil cover, soil nitrogen (N) and phosphorus (P) fertility, weed control and maize yields. The strategies tested are cover crop bicultures, selection of an adapted lupin cultivar and seeding rate, and the feasibility of rain fed winter cover cropping. The cover crop experiments were carried in rotation with summer maize between the winter of 2009 and summer of 2010/2011. Biculture trial was carried out by seeding oat (Avena sativa) and vetch (Vicia dasycarpa) at three mixture ratios and as sole crops under irrigation. On a separate irrigated trial, two lupin cultivars (Lupinus angustifolius var Mandelup & Qualinock) were seeded to a range of seeding rate, 40 to 220 kg ha-1. To study the feasibility of rain fed winter cover cropping, oat, vetch, rye (Lolium multiflorum), barley (Hordeum vulgare), radish (Raphanus sativa) and triticale (Triticale secale) were relayed into a maize crop in February, March and April of 2010. The irrigated trials were followed with SC701 maize cultivar, whilst the rain fed trial was followed with DKC61-25 maize cultivar. Bicultures gave higher cover crop biomass than sole vetch, increasing with an increase in the oat component of the mixture. Increased N and P uptake was observed with bicultures compared to sole oat, however, the levels were comparable to sole vetch. Sole vetch increased soil inorganic N and P at maize planting, whilst the slow decomposition by sole oat residue resulted in mineral lock up. Bicultured cover crop residues had intermediate decomposition rates and resulted in optimum levels of inorganic N and P for prolonged periods compared to sole crops. Weed suppression by the bicultures was comparable to sole cover crops. Biculturing technology significantly (P<0.05) increased maize grain yield compared to sole oat and the yields were comparable to those from sole vetch. For lupins, 206 kg ha-1 seeding rate gave the optimum biomass yield. Weed dry weights in both cover crop and maize crop decreased with an increase in lupin biomass. Comparable soil total N and inorganic P values at maize planting, were observed from plots planted to 120, 180 and 220 kg ha-1. Maize grain yield increased with an increase in lupin seeding rate. The study on rain fed winter cover cropping had most cover crop species’ biomass decreasing with each delay in planting except for radish, which increased. Vetch produced the highest amounts of biomass from February and March planting whilst radish had the highest biomass in April planting. The two species resulted in the greatest N improvement compared to the other species. Regardless of the grazing, the grass specie residues managed to persist to the next cropping season and the residue remaining were comparable to that of radish and vetch. Late-planted cover crops had the greatest residue remaining than early-planted, as a result, April planted cover crops provided better weed suppression than March and April planted. Vetch provided the highest maize grain yield (4005 kg ha-1) whilst all other species tested had comparable grain yields. The results suggested that bicultures could be grown to give sufficient biomass for both weed suppression and soil fertility improvement. Furthermore, increasing lupin plant densities improve its function as a cover crop with respect to weed suppression, soil fertility improvement and maize yields. The study also showed that for dry land systems, February and March planted vetch and April planted radish can provide the greatest biomass and maize yield improvement.

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

Cover crop use provides a myriad of benefits to soil health. Despite strong agronomic evidence of the benefits of using cover crops, farmers have been slow to adopt cover crop systems. Surveys show that this is due to a lack of understanding on how cover crop use will impact the farm, and limited economic analysis on the effects of cover crop use on the farm. <div> In this thesis, a variable-rate nitrogen study was analyzed to determine the relationship between applied nitrogen fertilizer and corn yields, and how a cover crop treatment impacts that relationship. Data were obtained from a case farm in Central Indiana. Production information was then translated into a partial budget to see how the use of the different cover crop treatments impacted net return per acre for corn production on the farm. Net returns were analyzed using both historical corn and nitrogen prices and stochastic modelling.</div><div> Results showed that the final impact on farm net return per acre associated with adoption of a cover crop system varies among cover crop species. Implementing annual rye resulted in a negative change to net return; while cereal rye and an oats and radish blend resulted in a positive change to net return. When additional benefits of cover crop use; such as drought tolerance, carbon content, and erosion reduction; are included, all three cover crop species resulted in a substantial increase in net return. This information will be of interest to farmers as a source to draw upon when making decisions regarding their own farms. Further research is needed to fully understand the relationship between cover crop use and farm profitability, particularly for farms at the early stages of adoption.</div>

Soil health-based agricultural management practices are widely promoted to improve soil structure, infiltration and reduce erosion. This study was conducted at two locations in North-Central Mississippi to evaluate the influence of different cover crop species and poultry litter on soil health that can impact crop production, climate change, and resilience. The results indicated that the cover crops showed a little effect on some soil health indicators compared to control treatment. However, in one location, rye, and a mixture of cover crops decreased bulk density and increased available water content and organic matter. The poultry litter had a positive effect on most soil physical and chemical health indicators. The cover crop species at Pontotoc decreased bulk density, increased field capacity, CEC, and total carbon. However, there was no significant effect of cover crops on most soil chemical health indicators, and soil responses may take more than five years for the changes to appear.

The transition of natural landscapes to intensive agricultural uses has resulted in severe loss of soil organic carbon (SOC), increased CO₂ emissions, river depletion, and groundwater overdraft. Despite negative documented effects of agricultural land use (i.e., soil erosion, nutrient runoff) on critical natural resources (i.e., water, soil), food production must increase to meet the demands of a rising human population. Given the environmental and agricultural productivity concerns of intensely managed soils, it is critical to implement conservation practices that mitigate the negative effects of crop production and enhance environmental integrity. In the Mississippi Alluvial Valley (MAV) region of Mississippi, USA, the adoption of cover crop (CC) and no-tillage (NT) management practices has been low because of a lack of research specific to the regional nuances. Therefore, this study assessed the long-term soil physiochemical and biological responses from integrating CC and NT management to agricultural soils of the region. Research plots were established in a split-block design with two tillage treatments: NT and reduced tillage (RT) and three CC treatments: no cover (NC), rye (RY) and a rye+clover (RC) mix. Soil samples were taken during the growing season of 2019 and 2020. Bulk density was found to be significantly lower in NT plots and aggregate stability was greatest in plots with a single CC species. Moisture retention increased in NT.. Soil organic carbon was greater in NT and CC treatments and there was no difference in CO₂ flux. Bacterial abundance had a positive effect on SOC but a negative effect on CO₂. The rate of proportional change and pattern of variability in C pools suggested loss of SOC in reduced tillage (RT) treatments. Microbial abundance, functional genes and enzyme activity was greater in NT with CC, but diversity was greater in RT. No-tillage practices lower diversity and influence long-term community changes while CC practices enact a seasonal response to environmental conditions. I conclude that in heavy clay soils of the mid-South region of the MAV, RT with a CC is optimal for soil health traits associated with crop sustainability, however the management will still contribute to increased CO₂ emissions.