Master of Science / Department of Agronomy / Dorivar Ruiz Diaz / The application of micronutrients to increase yields has become more popular with increased commodity prices and higher yielding crops. Two studies were completed evaluating secondary and micronutrient for soybean (Glycine max [L.] Merr.) and wheat (Triticum aestivum).The objective of the first study was to evaluate the response of soybean, under a double crop system after wheat, to soil-and foliar-applied macro and micronutrients. Macronutrients (N, P, K) were applied at 22 kg ha[superscript]-[superscript]1, micronutrients (Fe, Mn, Zn) were soil applied at 11 kg ha[superscript]-[superscript]1and S was applied at 22 kg ha[superscript]-[superscript]1. Plant response parameters were evaluated including changes in nutrient concentration, and seed yield response. Tissue samples were collected at the respective R1 growth stage. Samples were analyzed for the nutrients applied with the fertilizer treatments. Soybean seed yield slightly responded to soil-applied S, Mn, and Zn. When micronutrients were foliar-applied, seed yield was significantly decreased. The second study evaluated the application of S and micronutrients to winter wheat. The objectives were to evaluate the wheat response to sulfur and micronutrient fertilization and evaluate soil testing and tissue analysis as diagnostic tools. Fertilizer treatments consisted of sulfur, iron, manganese, zinc, boron, copper. All of the micronutrients were sulfate-based products and the sulfur treatments were applied as gypsum. Fertilizer treatments were applied as topdress in early spring. Soil samples were collected before fertilizer application and after harvest. Flag leaf samples were collected and analyzed for the nutrients applied with the fertilizer treatments. Significant increases in tissue concentration were observed when Zn, B, and S were applied. Significant increases in soil test Zn, Cu, B, and S were observed compared to the control treatment. Despite the increases in soil test concentration across locations, no significant increases in yield by any of the nutrients or combination of nutrients were observed.

Master of Science / Department of Agronomy / Dallas E. Peterson / Auxin herbicides have been widely used for broadleaf weed control since the mid-1940’s. With new auxinic herbicide-resistant traits in corn, soybean, and cotton, use of these herbicides is likely to increase. Glyphosate-resistant Palmer amaranth (Amaranthus palmeri) and common waterhemp (Amaranthus rudis) are two primary problematic weed species that will be targeted with dicamba and 2,4-D in the new systems. No-till double-crop soybean after winter wheat harvest is a popular cropping system in central and eastern Kansas, however, management of glyphosate resistant Palmer amaranth has become a serious issue. Field experiments were established near Manhattan and Hutchinson, KS, in 2016 and 2017, to compare seventeen herbicide treatments for control of Palmer amaranth and large crabgrass (Digitaria sanguinalis) in dicamba/glyphosate resistant no-till double-crop soybean after winter wheat. Herbicide programs that included a residual preemergence (PRE) treatment followed by a postemergence (POST) treatment offered greater Palmer amaranth control 8 weeks after planting when compared to PRE-only, POST-only and burndown-only treatments. All treatments that contained glyphosate POST provided complete control of large crabgrass compared to less than 43% control with PRE-only treatments. Soybean grain yield was greater in programs that included PRE followed by POST treatments, compared to PRE-only and burndown-only treatments. A second set of field experiments were established in 2017 near Manhattan and Ottawa, KS to evaluate dicamba and 2,4-D POST efficacy on Palmer amaranth and common waterhemp. Five rates of dicamba (140, 280, 560, 1121, and 2242 g ae ha⁻¹) and 2,4-D (140, 280, 560, 1121, and 2242 g ae ha⁻¹) were used to evaluate control of the Amaranthus spp. Each experiment was conducted twice at each location. Dicamba provided better Palmer amaranth and common waterhemp control than 2,4-D across the rates evaluated. Control of Palmer amaranth was 94% and 99% with dicamba rates of 1121 and 2242 g ae ha⁻¹, respectively, but 2,4-D never provided more than 80% control at any rate. The highest rates of both dicamba and 2,4-D provided greater than 91% common waterhemp control, but control was less than 78% with all other rates of both herbicides. Palmer amaranth and common waterhemp control did not exceed 73% with the highest labelled POST rates of either dicamba or 2,4-D. Auxinic herbicide-resistant traits in corn, soybean, and cotton offer new options for controlling glyphosate-resistant Palmer amaranth and common waterhemp, however proper stewardship is vital to maintain their effectiveness.

Master of Science / Department of Agronomy / Johanna A. Dille / An opportunity for postemergence (POST) grass weed control has recently been approved with ALS-resistant grain sorghum, however, grass weed emergence timing and crop tolerance to grass competition are not well understood. To address the importance of POST application timing, a critical period of weed control (CPWC) for grass competition in grain sorghum was developed. Field experiments were established near Manhattan and Hays, KS in 2016 and 2017, and near Hutchinson, KS in 2017 to determine the CPWC. Each site provided a different grass species community. A total of ten treatments were included, with four treatments maintained weed-free until 2, 3, 5, or 7 weeks after crop emergence, four treatments receiving no weed control until 2, 3, 5, or 7 weeks after crop emergence, and two treatments were maintained weed-free or weedy all season. Treatments did not influence grain yield at Hutchinson because of a lack of season-long weed emergence. At Hays the CPWC began at crop emergence and ended 28 days later. At Manhattan the CPWC began 27 days after emergence and continued through grain harvest. The CPWC in grain sorghum depends on rainfall and competitive ability of the weed species. The start of the CPWC began when weeds emerged, thus a POST application should be targeted 14 to 21 days after emergence of grain sorghum. Emergence and development of large crabgrass, barnyardgrass, shattercane, and giant, green, and yellow foxtails were studied near Manhattan, KS after seeding on April 11, 2017. Barnyardgrass had the longest duration of emergence, beginning at 180 GDD after seeding and continuing through July. Large crabgrass had the shortest duration of emergence from 325 to 630 GDD after seeding. In general, all grasses began to emerge in late April and most species completed 90% emergence by early June. Grain sorghum is typically planted at this time, so grass weed control prior to planting is critical. Palmer amaranth is a troublesome weed in double-crop grain sorghum production fields in Kansas. The presence of herbicide-resistant populations limits options for weed management. Field experiments were conducted to evaluate 14 different herbicide programs for the management of atrazine-resistant Palmer amaranth in double-crop grain sorghum at Manhattan and Hutchinson, KS in 2016 and 2017. Programs included eight PRE only and six PRE followed by POST treatments. Programs that had very long chain fatty acid-inhibiting herbicides provided greater control of atrazine-resistant Palmer amaranth by three weeks after planting sorghum. Programs of PRE followed by POST provided greater control of both atrazine-resistant and -susceptible Palmer amaranth by eight WAP compared to PRE alone. These results illustrate the value of residual herbicides, as well as an effective postemergence application, in double-crop grain sorghum. Early season grass and Palmer amaranth control with the use of residual herbicides such as very long chain fatty acid-inhibitors provide a competitive advantage to grain sorghum. Utilizing weed emergence patterns to time effective POST applications, in unison with residual herbicides, will provide season-long weed control in Kansas grain sorghum fields.

Devido as poucas opções de cultivo, o cotonicultor em Mato Grosso concentra seu modelo de produção em algodão, soja e milho, o que tem contribuido para que o estado seja o maior produtor nacional dessas três culturas. Nas últimas safras, a produção algodão migrou para segunda safra, dividindo espaço com o milho e colocando a soja como principal opção do cultivo de verão. Além disso, nas última cinco safras, as mudanças de tecnologias de sementes de algodão foram intensas, alterando ainda mais os sistemas produtivos. Em virtude das recentes mudanças, dúvidas ainda residem sobre a eficiência financeira-econômica e o risco assumido com o novo modelo produtivo. Partindo dessa lacuna na pesquisa, o estudo teve como objetivo descrever como as propriedades de algodão se configuraram entre as safras 2012/13 e 2015/16, para subsidiar a mensuração dos risco das cultivos de algodão, soja e milho e seus respectivos sistemas. Ao final, o estudo buscou construir um modelo que otimize a renda e risco da combinação dos cultivos (algodão safra, soja, algodão 2ª safra e milho 2ª safra), para auxiliar na gestão da propriedade rural. Para fins de estudar todos os sistemas produtivos, foram delimitadas duas regiões: Agregado Norte e Centro Leste. A primeira compreende a produção de soja no verão e algodão e milho na segunda safra, enquanto a segunda se restringe ao cultivo de algodão e soja no verão e milho sucedido pela oleaginosa. Para análise de risco dos cultivos e sistemas de produção, foi utilizado o método de Monte Carlo, por envolver simulação de elementos aleatórios. Para construção de uma fronteira de eficiência das possiveis combinações de culturas na propriedade analisando a relação retorno-risco, o algorismo genético foi base para o modelo de otimização via simulação. Os resultados apontam a produção de soja com o menor risco, enquanto sistemas com segunda safra são mais arriscados. No entanto, a introdução do algodão em sucessão a soja trouxe ganhos significativos de receita líquida para o sistema, enquanto o milho 2ª safra pouco aumentou a renda ou então reduziu em resposta a grande aumento do risco de produção. No geral, o Centro Leste mostrou-se menos arriscado para produção de algodão e grãos, principalmente no que tange a produtividade. Sob a teoria do portfólio, os dados do modelo mostram que a utilização de soja na totalidade de área de verão resulta em maiores ganhos de rentabilidade, enquanto que a maximização da renda ocorre com acréscimo de área do algodão na primeira safra, mas que que por outro lado expõe a fazenda a maior risco de produção. A introdução de área na segunda safra ajuda a atenuar os riscos da propriedade. Sendo assim, a diversificação de culturas na propriedade se mostrou o melhor caminho para gerir o risco, dado que a utilização do maior número de cultivos resultou nas melhores relação entre retorno e risco. / With the few cultivation options, the cotton-grower in Mato Grosso concentrates its production model on cotton, soybeans and corn, which has contributed to the state being the largest national producer of these three crops. In the last harvests, cotton production migrated to the double harvest model, dividing space with corn and placing soybeans as the main option of summer cultivation. In addition, in the last five harvests, cotton seed technologies changes were intense, further shifting the production systems. Due to the recent changes, doubts still rest on the financial-economic efficiency and the risk assumed with the new production model. Based on this lacuna in the research, the objective of this study was to describe how cotton properties were configured between the 2012/13 and the 2015/16 harvests, to subsidize the measurement of the risk of cotton, soybean and corn crops and their respective systems. At the end, the study develops a model that optimizes the income and risk of the crop combination (crop cotton, soybean, 2nd cotton crop and second corn harvest), to assist the rural property management. To study all the productive systems, two regions were delimited: North Aggregate and Eastern Center. The first comprises the production of soybeans in the summer and cotton and corn in the second crop, while the second is restricted to the cotton and soybeans cultivation in the summer and corn succeeded by the oilseed. For the analysis of the crops and production systems risk, the Monte Carlo method was used, involving random elements simulation. To build an efficient frontier of possible combinations of crops in the property, analyzing the return-risk relationship, the genetic algorithm was the basis for the simulation optimization model. The results point to the soybeans production being the one with the lowest risk, while systems with second harvests are more risky. However, the introduction of cotton in succession to soybeans brought significant net revenue gains to the system, while the second corn crop little increased the income or else reduced in response to the large increase in production risk. The Eastern Center proved to be less risky for cotton and grain production, especially in terms of productivity. In the portfolio theory, model data show that soybean cultivation in the entire summer area results in higher profitability gains, while revenue maximization occurs with cotton area increase in the summer crop, but exposes the farm to the highest production risk. The introduction of area in the second harvest helps to mitigate property risks. Thus, the crops diversification in the property proved to be the best route for risk management, as the use of the greatest number of crops resulted in the best relation between return and risk.

Devido as poucas opções de cultivo, o cotonicultor em Mato Grosso concentra seu modelo de produção em algodão, soja e milho, o que tem contribuido para que o estado seja o maior produtor nacional dessas três culturas. Nas últimas safras, a produção algodão migrou para segunda safra, dividindo espaço com o milho e colocando a soja como principal opção do cultivo de verão. Além disso, nas última cinco safras, as mudanças de tecnologias de sementes de algodão foram intensas, alterando ainda mais os sistemas produtivos. Em virtude das recentes mudanças, dúvidas ainda residem sobre a eficiência financeira-econômica e o risco assumido com o novo modelo produtivo. Partindo dessa lacuna na pesquisa, o estudo teve como objetivo descrever como as propriedades de algodão se configuraram entre as safras 2012/13 e 2015/16, para subsidiar a mensuração dos risco das cultivos de algodão, soja e milho e seus respectivos sistemas. Ao final, o estudo buscou construir um modelo que otimize a renda e risco da combinação dos cultivos (algodão safra, soja, algodão 2ª safra e milho 2ª safra), para auxiliar na gestão da propriedade rural. Para fins de estudar todos os sistemas produtivos, foram delimitadas duas regiões: Agregado Norte e Centro Leste. A primeira compreende a produção de soja no verão e algodão e milho na segunda safra, enquanto a segunda se restringe ao cultivo de algodão e soja no verão e milho sucedido pela oleaginosa. Para análise de risco dos cultivos e sistemas de produção, foi utilizado o método de Monte Carlo, por envolver simulação de elementos aleatórios. Para construção de uma fronteira de eficiência das possiveis combinações de culturas na propriedade analisando a relação retorno-risco, o algorismo genético foi base para o modelo de otimização via simulação. Os resultados apontam a produção de soja com o menor risco, enquanto sistemas com segunda safra são mais arriscados. No entanto, a introdução do algodão em sucessão a soja trouxe ganhos significativos de receita líquida para o sistema, enquanto o milho 2ª safra pouco aumentou a renda ou então reduziu em resposta a grande aumento do risco de produção. No geral, o Centro Leste mostrou-se menos arriscado para produção de algodão e grãos, principalmente no que tange a produtividade. Sob a teoria do portfólio, os dados do modelo mostram que a utilização de soja na totalidade de área de verão resulta em maiores ganhos de rentabilidade, enquanto que a maximização da renda ocorre com acréscimo de área do algodão na primeira safra, mas que que por outro lado expõe a fazenda a maior risco de produção. A introdução de área na segunda safra ajuda a atenuar os riscos da propriedade. Sendo assim, a diversificação de culturas na propriedade se mostrou o melhor caminho para gerir o risco, dado que a utilização do maior número de cultivos resultou nas melhores relação entre retorno e risco. / With the few cultivation options, the cotton-grower in Mato Grosso concentrates its production model on cotton, soybeans and corn, which has contributed to the state being the largest national producer of these three crops. In the last harvests, cotton production migrated to the double harvest model, dividing space with corn and placing soybeans as the main option of summer cultivation. In addition, in the last five harvests, cotton seed technologies changes were intense, further shifting the production systems. Due to the recent changes, doubts still rest on the financial-economic efficiency and the risk assumed with the new production model. Based on this lacuna in the research, the objective of this study was to describe how cotton properties were configured between the 2012/13 and the 2015/16 harvests, to subsidize the measurement of the risk of cotton, soybean and corn crops and their respective systems. At the end, the study develops a model that optimizes the income and risk of the crop combination (crop cotton, soybean, 2nd cotton crop and second corn harvest), to assist the rural property management. To study all the productive systems, two regions were delimited: North Aggregate and Eastern Center. The first comprises the production of soybeans in the summer and cotton and corn in the second crop, while the second is restricted to the cotton and soybeans cultivation in the summer and corn succeeded by the oilseed. For the analysis of the crops and production systems risk, the Monte Carlo method was used, involving random elements simulation. To build an efficient frontier of possible combinations of crops in the property, analyzing the return-risk relationship, the genetic algorithm was the basis for the simulation optimization model. The results point to the soybeans production being the one with the lowest risk, while systems with second harvests are more risky. However, the introduction of cotton in succession to soybeans brought significant net revenue gains to the system, while the second corn crop little increased the income or else reduced in response to the large increase in production risk. The Eastern Center proved to be less risky for cotton and grain production, especially in terms of productivity. In the portfolio theory, model data show that soybean cultivation in the entire summer area results in higher profitability gains, while revenue maximization occurs with cotton area increase in the summer crop, but exposes the farm to the highest production risk. The introduction of area in the second harvest helps to mitigate property risks. Thus, the crops diversification in the property proved to be the best route for risk management, as the use of the greatest number of crops resulted in the best relation between return and risk.

Maximizing productivity and profitability are the primary reasons for double-cropping soybean with small grain in the Mid-Atlantic, USA. Reduced double-crop yield can be attributed to: delayed planting that results in a shortened growing season and less vegetative growth; later-maturing cultivars that terminate main stem growth after flowering and have less growth and nodes; less soil moisture and plant-available nutrients due to small grain uptake; greater air and soil temperatures during vegetative stages that reduce early-season growth; and more favorable conditions for disease development during pod and seed formation. Field experiments were conducted in 2012 and 2013 in eastern Virginia to 1) evaluate cultivar stem growth habit, seeding rate, seed-applied inoculant, starter nitrogen (N) applied at planting, and foliar fungicide on soybean vegetative growth, total N uptake (TNU), seed yield and quality, and yield components; 2) determine the effect of starter N rate, applied with and without inoculant, on soybean vegetative growth, TNU, seed yield and quality, and yield components; and 3) evaluate the response of maturity group (MG) IV and V soybean cultivars to foliar fungicide. Greater seeding rates, inoculant, N, and fungicide typically were not required together to increase yield. Although cultivar interacted with other factors, early-maturing indeterminate 95Y01 yielded more than late-maturing determinate 95Y20 at 4 of 6 locations. Seeding rate interacted with other factors, but the greater seeding rate increased MG IV yield at 1 of 6 locations and decreased MG V yield at 2 of 6 locations. Starter N increased seed yield by 6 kg ha-1 per kg N applied until yield plateaued at 16 kg N ha-1, which continued to 31 kg N ha-1. When N rate was increased greater than 31 kg N ha-1, yield decreased. Fungicide increased yield for MG IV and V cultivars at 4 of 6 and 3 of 6 locations, respectively and prevented yield loss via mid- to late-season disease control, delayed leaf drop, and greater seed size. Optimum fungicide timing depended on environment and disease development. These data assisted in understanding agronomic inputs' combined or individual effects on double-crop soybean growth, canopy, N uptake, seed yield, and yield components. / Ph. D.

The Midwestern United States is a nationally and globally important producer of agricultural products and uses intensive practices to achieve high grain yields. However, intensive agriculture is a major contributor of nitrogen and phosphorus export to the Mississippi River and the hypoxic zone in the Gulf of Mexico. Cover cropping is a recommended conservation practice for providing soil cover throughout the winter and taking up nutrients that may otherwise be lost in bare fallow systems, but the associated costs limit widespread adoption of this practice. Double cropping, which involves growing two crops in one year, is functionally similar to cover cropping and can be harvested for an additional income, but the water quality impacts of applying fertilizer to maximize yields and the systemic impacts of intensification with another crop on corn-soybean rotations are not well understood. This two-year, plot scale study in Carbondale, Illinois was designed to assess nutrient leaching, referring to nitrate-N, ammonium-N, and dissolved reactive phosphorus (DRP), nutrient availability, and crop yields when using bare fallow, cereal rye (Secale cereale) cover crops, or winter wheat (Triticum aestivum) double crops with varying nitrogen fertilizer rates and timings in the winter seasons of corn-soybean rotations. Four blocks with randomly assigned treatments comprised of two treatment factors were used. These treatment factors included rotations with either bare fallow or cover crops in alternate winters and winter wheat fertilizer management intensity with a high fertilizer treatment level, grower recommended rates applied at planting, tillering, and jointing, a medium fertilizer treatment level, grower recommended rates applied at tillering and jointing, a low fertilizer treatment level, with reduced nitrogen rates applied at tillering and jointing, and a no fertilizer treatment level, which was used as either corn-soybean or corn-cover crop-soybean-cover crop control. Additional nutrient inputs from fertilizers in the winter wheat seasons did not significantly increase nitrate-N, ammonium-N, or DRP leaching in the 2021-2022 winter wheat sampling season and nitrate-N and ammonium-N leaching was significantly less in some or all the winter wheat plots compared to the control plots. Winter wheat yields and nitrogen uptake in 2022 were significantly greater in medium fertilizer plots while yield-based nitrogen leaching and partial nitrogen balances were significantly greater in high fertilizer treatments, indicating that delayed fertilization in winter wheat can improve nitrogen use efficiency and yields. Soybean yields were significantly greater in plots without winter wheat due to a longer growing season, but plant available ammonium-N concentrations, which were greater in winter wheat plots, also had a significant negative relationship with soybean yields, indicating that this may have impeded biological nitrogen fixation. Using cover crops in alternate winters reduced nitrate-N leaching by 106% and plant available nitrate-N concentrations by 107% in the season as well as the subsequent corn season by 66% and 90%, respectively, compared to the bare fallow plots, and the decreased plant available nitrate-N concentrations in cover crop plots caused a 6% yield penalty in the corn harvest. Despite yield penalties to cash crops from winter crops, the use of double crops was the only factor that significantly impacted total crop yields. The use of cover crops in alternate winters was the most significant factor in nutrient leaching, demonstrating that these practices can be used to increase total crop yields without contributing significantly to nutrient export. For farmers concerned with the costs of cover cropping, double cropping is a practice that can provide some of the same ecosystem services while also providing an additional financial incentive.

Master of Science / Department of Agronomy / P. V. Vara Prasad, / Kraig L. Roozeboom / Replacing fallow with cover crops can provide many benefits, including improved soil quality and reduced nitrogen fertilizer requirements. The addition of cover crops into no-till systems has become popular in recent years as a means of increasing cropping system intensity and diversity. A primary concern of producers in the Great Plains is the possibility that cover crops may reduce the amount of soil water stored in the profile for the next grain crop, potentially reducing yields. Multi-species cover crop mixtures that enhance the ecological stability and resilience of cover crop communities may produce greater and more consistent biomass than single species. Field experiments were established in 2013 and 2014 near Belleville and Manhattan, KS following winter wheat (Triticum aestivum L.) harvest to evaluate the effect of cover crop species and species complexity on changes in soil profile water content and water use efficiency. Along with a chemical fallow control, ten cover crop treatments were tested: six single species, two-three component mixes, a mix of six species, and a mix of nine species. Volumetric water content was measured using a neutron probe and a Field Scout TDR 300. Similar data were collected in 2014 from an experiment established in 2007 comparing fallow, double-cropped soybean, and four cover crop types (summer and winter legumes and non-legumes) in a no-till winter wheat-grain sorghum-soybean cropping system near Manhattan, KS. Results from both studies showed that grasses produced the most dry matter with the highest water use efficiency (up to 618 kg cm-1). Fallow lost up to 7.9 cm less water than all cover crop treatments throughout cover crop growth and in the fall, but captured up to 3.4 cm less moisture in the spring than the cover crops that added residue to the soil surface. Brassica species extracted water from deeper in the soil profile than the other cover crop species. Species complexity affected water use only relative to the proportions and productivity of their individual components, with no advantage in water use efficiency for the more complex mixtures.

Feed grain consumption in Virginia and the mid-Atlantic region is more than double the total production. Producing more feed grains in this region could generate more profit for grain growers and lower costs for end-users. Increased feed grain production in this region will necessitate improved corn (Zea mays L.) management techniques and adoption of alternative feed grains such as grain sorghum (Sorghum bicolor L.). In order to achieve our overall objective of increased corn and grain sorghum production in the region, experiments were conducted to assess tools with the ability to increase the efficiency of sidedress nitrogen (N) application for corn and to test the performance of grain sorghum in both full season and double-crop rotations in this region. For the corn studies, seven field experiments were established in 2012-2014 with four replications in a randomized complete block design. Treatments included a complete factorial of four different preplant N rate (0, 45, 90, 134 kg ha-1) with three different approach simulation model-prescribed rates (Virginia Corn Algorithm, Maize-N, Nutrient Expert-Maize) and the standard Virginia yield-goal based approach. No differences in corn yield were found between the different simulation model and preplant N rate, however the prescribed sidedress N rate varied significantly due to the simulation model, preplant N rate and the interaction between them. The nitrogen use efficiency (NUE) was estimated based on partial factor productivity (PFP) of nitrogen. The greatest PFP resulted from use of the Virginia Corn Algorithm (VCA), which produced 68 kg grain kg N-1 compared with 49 kg grain kg N-1 for the yield-goal based approach. While the VCA shows promise as a tool for improving NUE of sidedress applications in corn, more research is needed to validate performance. Soybean (Glycine max L.) is often double-cropped after small grain in the mid-Atlantic region. Growing grain sorghum in this niche in the cropping system instead could result in greater overall feed grain production. In order to assess the performance of grain sorghum as an alternative in common cropping systems, four field experiments were established at the Southern Piedmont Agriculture Research and Extension Center (SPAREC) and Tidewater Agriculture Research and Extension Center (TAREC), near Blackstone and Holland, Virginia, respectively. The experiments were conducted using a split plot design with four replications and fourteen treatments. Main plot was winter small grain crop; either barley (Hordeum vulgare L.), triticale (x Triticosecale.), wheat (Triticum aetivum L.) or winter-fallow and the subplot either soybean or sorghum. In three of four instances, full season sorghum yields were greater than double-cropped sorghum after small grain. At two locations, sorghum yields following triticale were lower than when following barley, possibly indicating an antagonistic or allelopathic effect of triticale. The most profitable cropping system was wheat-soybean based on the price assumptions and measure yields in this experiment. Among the sorghum cropping system, the most profitable system was also wheat-sorghum. Sorghum can be successfully grown in both full-season and double-crop systems and offers good potential to increase feed grain production in this region. / Ph. D.

The occasional failure of glyphosate to control all weeds throughout the entire growing season has prompted growers to sometimes use herbicides other than glyphosate on glyphosate-tolerant soybean. Field studies were conducted in 1999 and 2000 to investigate potential crop injury from several herbicides on glyphosate-tolerant soybean, and to determine the relationship between soybean maturity, planting date, and herbicide treatment on soybean injury, leaf area index (LAI), and yield. Three glyphosate-tolerant soybean cultivars representing maturity groups III, IV and V were planted at dates representing the full-season and double-crop soybean production systems used in Virginia. Within each cultivar and planting date, 15 herbicide treatments, in addition to a control receiving only metolachlor preemergence, were applied to cause multiple levels of crop injury. Results of this study indicate that glyphosate-tolerant soybean generally recovered from early-season herbicide injury and LAI reductions; however, reduced yield occurred with some treatments. Yield reductions were more common in double-crop soybean than in full-season soybean. In full-season soybean, most yield reductions occurred only in the early maturing RT-386 cultivar. These yield reductions may be attributed to the reduced developmental periods associated with early maturing cultivars and double-crop soybean that often lead to reduced vegetative growth and limited LAI. Additional reductions of LAI by some herbicide treatments on these soybean may have coincided with yield reductions; however, reduced LAI did not occur with all yield reducing treatments. Therefore, soybean LAI response to herbicide treatments does not always accurately indicate the potential detrimental effects of herbicides on soybean yield. Further, yield reductions associated with herbicide applications occurred, although soybean sometimes produced leaf area exceeding the critical LAI level of 3.5 to 4.0 which is the minimum LAI needed for soybean to achieve maximum yield. / Master of Science