Weeds and soil-borne diseases can cause large yield losses in field-grown tomato (Solanum lycopersicum) production. Techniques have been developed to reduce soil-based problems. In this study, we evaluated the impacts of cover crops, soil steaming, and plastic mulch to reduce weed and disease pressure in field-grown tomatoes. Four cover crop treatments were grown in the fall and winter before spring planting. Soils were steamed to a target temperature of 71.1 °C for 0, 5, or 20 minutes. Plastic mulch was also used on half of the rows. Yield, weed densities, and disease incidence were recorded. Reduced flowering time and stringent flowering requirements may reduce the ability to conduct crosses in many plants. Many factors control flowering. Terminal Flowering Locus 1 (TFL1) inhibits flower development. In this study, we attempted to transiently downregulate TFL1 via virus-induced gene silencing (VIGS) in Antirrhinum, Penstemon, Petunia, Rosa, and Rudbeckia.

This study analyzes the change in whole-farm net revenues and nutrient reduction from the implementation of five best management practices (BMPs) on a typical beef and beef-poultry farm in Shenandoah County. Whole-farm net revenues, resource allocation, nutrient loss reductions, and the cost efficiency of reducing nutrient losses were analyzed to assess which BMPs are the most cost efficient to implement, assuming the baseline scenarios have no voluntarily applied BMPs. The effects of stacking additional BMPs, in combinations of two or more, were also assessed. No-till cropping, winter wheat cover crop, herbaceous riparian buffer, fencing, and P-based NMP were the BMPs that were analyzed. Incentive payments from state and federal governments were incorporated into the cost of BMP adoption. A brief analysis of a farmer's time value of money, with respect to incentive payments, was also conducted. Results indicated that no-till crop management was the most cost efficient BMP, and was the only BMP to increase net revenues for both farm models. Fencing and P-based NMP were the least cost efficient for the beef farm. For the beef-poultry farm, fencing was the least cost efficient. The implications of this study are that farmers that choose to adopt BMP should evaluate both their interests in maintaining (or increasing) farm net revenues along with their interest in improving water quality through the reduction of nutrient losses. There is potential for implementing multiple BMPs, while increasing net revenues from a farm's baseline scenario. For farmers and policy makers, no-till cropping can be a profitable and therefore cost efficient BMP to implement. Incentive payments are intended to encourage the adoption of BMPs by subsidizing a portion of the start-up costs. Policy makers should attempt to make cost-share payments reflect nutrient reduction goals. This can be done by analyzing both the compliance cost to farmers and the nutrient reduction effectiveness of BMPs. / Master of Science

Cover crops are often planted during the fallow periods of cash crop harvests to cover the soil and reduce erosion but also to provide other ecosystem benefits including capturing residual nutrients and thus, reducing environmental losses of nitrogen (N) and phosphorus (P) in agroecosystems. Among these cover crops, winter rye (Secale cereale) is popular due to its winter hardiness and relatively cheap seed costs. However, growers in the Midwest, USA are reluctant to use winter rye prior to corn (Zea mays L.) due to the potential yield penalty in corn. This thesis introduces two strategies that could minimize winter rye’s effect on corn while providing nutrient loss reduction benefits are precision planting and reducing the seeding rate of winter rye ahead of corn. One study evaluates whether precision planting (planting winter rye strategically to avoid intersecting zones with corn) of winter rye at low seeding rate (37.5 kg ha-1) could produce similar cover crop biomass and quality to normal planted winter rye (50 kg ha-1) and if precision planting can improve performance and N requirement of corn (Chapter 1). The study was conducted in central Indiana during 2020-2021 (CIN21), and southern Illinois during 2021-2022 (SIL22), and 2022-2023 (SIL23) growing seasons. The experiment was arranged in a randomized block design with split plot arrangement. Main plots were three cover crops (a no-cover crop control (NoCC), conventional planted winter rye (CR), and precision planted winter rye (PR). Subplots were six rates of N fertilizer that ranged from 0-280 kg ha-1 for the CIN21 and 0-359 kg ha-1 for SIL22 and SIL23. Our results indicated that shifting from normal planting to precision planting resulted in similar cover crop biomass production with limited effect on winter rye quality [N concentration, Carbon (C):N ratio] and N and C accumulation. In CIN21, the no-cover crop control had higher yield and lower N requirements which was consistent with those of SIL22. The economic optimum rate of N (EORN) was below the typical recommended range for central Indiana and was above the recommended range for southern Illinois. Precision planting resulted in a slight increase in corn yield and N requirement, but overall was more profitable than normal planting due to a reduction in the number of seeds required and higher corn to fertilizer prices. Therefore, we recommend that (i) decision support tools for N management in corn should be revised for addition of cover crops in the Midwest, and (ii) precision planting should be implemented instead of normal planting for greater economic benefit. Future research should evaluate ecosystem services of precision vs. normal planting of winter rye over time. The other study evaluates whether planting method of winter rye (precision vs. conventional) at medium and low seeding rates of winter rye influence cover crop biomass production, N and C concentrations and accumulations, and corn performance (Chapter 2). A trial was conducted in 7 site-yrs in Indiana and Illinois during 2020-2021, 2021-2022, and 2022-2023 growing seasons. The trial was arranged in a randomized complete block design with four replicates. Cover crops [conventional planting (CR) and precision planting (PR)] were factorially arranged with two seeding rates (18.75 vs. 37.5 kg ha-1) for PR and (25 vs. 50 kg ha-1) for CR. Two extra treatments were included as control which were no-cover crop with zero-N and a 224 kg N ha-1 addition to corn. Cover crop biomass, C, N, their uptake, and C:N ratio were evaluated along with corn plant population, and corn grain yield. Our results indicated that winter rye had similar aboveground biomass, N uptake, and C accumulation regardless of planting method and seeding rate suggesting a precision planting at low seeding rate is most economical for cover crop establishment. Corn plant population was only affected by winter rye in one site-yr (CIL23) in which precision planting did not help with minimizing the negative effect of winter rye on corn population. In this study, lack of N fertilization did not decrease corn population but significantly reduced corn grain yield in all site-yrs. Corn grain yield was similar among cover crop treatments (with exception of no cover crop no N) but in one of the site-yrs, precision planting at 18.75 kg ha-1 resulted in greater corn yield than the no-cover crop with 224 N ha-1. We concluded that growers that plant winter rye prior to corn could use precision planting at a seeding rate of 18.75 kg ha-1 to take up residual soil N with limited interference with corn production at a reduced cost compared to conventional winter rye management.

No description available.

<p dir="ltr">Cover crops and soil residual herbicides are some of the essential tools within the integrated weed management. When used at cover crop termination, residual herbicides can extend the period of weed control and reduce the selection pressure for herbicide resistance. However, previous research has indicated that the use of cover crops can increase the microbial activity of the soil which, in turn, is the primary route for herbicide degradation in the soil. In addition to the potential effect on the microbial breakdown of herbicides, cover crops can also alter the fate of herbicides by interception. Three field projects were established to (1) investigate the influence of cover crop [cereal rye (<i>Secale cereale</i> L.) and crimson clover (<i>Trifolium incarnatum</i> L.)] use on soil enzyme activities [β-glucosidase (BG) and dehydrogenase (DHA)], its effect on the concentration of residual herbicides (sulfentrazone, <i>s</i>-metolachlor, cloransulam-methyl, atrazine, and mesotrione) in the soil, and the interception of herbicides by cover crop residue; (2) to investigate the effect of cover crop termination strategies (fallow, standing, and roller crimped 1 d prior to application) and simulated rainfall volumes (0, 4.2, and 8.3 mm simulated over 20 min; equivalent to 0, 12.5, and 25 mm h^-1) on atrazine wash off from cereal rye biomass onto the soil; (3) to investigate the effect of cereal rye termination strategies on the concentration of sulfentrazone, <i>s</i>-metolachlor, and cloransulam-methyl in the soil, weed control, and soybean [Glycine max (L.) Merr.] yield.</p><p dir="ltr">Results from the first project suggests that the use of cover crops occasionally resulted in increased BG and DHA activities relative to the fallow treatment. However, even when there was an increase in the activity of these two enzymes, increased degradation of the residual herbicides was not observed. Furthermore, the use of cereal rye or crimson clover as cover crops did not reduce the efficacy of the residual herbicides in controlling weeds early in the growing season.</p><p dir="ltr">In regards to the fate of atrazine after simulated rainfall, the results from the second project indicated that cereal rye biomass accumulation negatively impacted the amount of herbicide reaching the soil at the time of application. Although the roller crimped cereal rye reduced the amount of herbicide reaching the soil relative to the standing cereal rye, it also reduced atrazine leaching below the 0-5 cm of soil. Furthermore, in cover cropping systems with high levels of cereal rye biomass, more than 8.3 mm of rain are required to wash most of the atrazine off of the biomass.</p><p dir="ltr">Lastly, the adoption of the planting green systems resulted in up to 84% interception of residual herbicides by the roller crimped cereal rye biomass. The use of cereal rye as cover crop did not improve the weed control relative to the fallow during the two years of field research. Soybean yield losses ranged from 10 to 44% with the adoption of the planting green system, primarily due to stand losses. However, there are strategies and proper equipment available that can be used to minimize soybean stand losses.</p>

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.

Economic and environmental concerns surrounding nitrogen (N) have motivated efforts to improve estimates of plant available N in soil in order to improve crop N management decisions. Cover crops have been recognized as an effective tool for protecting soil and enhancing soil function including N cycling. This recognition has increased the adoption of cover cropping in the United States. Despite this growing popularity, there is lack of consistent response of cover crop on soil health and only a few experiments have examined how cover crop impacts nitrogen (N) management in corn. Therefore, the objectives of this study were to: a) quantify the impacts of cover crops on various soil health indicators like permanganate oxidizable carbon (POXC), CO2 burst, autoclaved-citrate extractable (ACE)-soil protein, b) investigate the relationship between soil health indicators, soil nitrate (NO3-N) and ammonium (NH4-N), corn N requirement and corn yield, and c) study the decomposition and N release of different cover crops. In a comparison of cover crop treatments, there was a trend of increasing permanganate oxidizable carbon (POXC) and CO2 burst with cover crop compared to no-cover crop control in the short term (1 year). Additionally, CO2 burst values were significantly increased for a long-term site with cover crops compared to the control in both 2021 and 2022. A long-term cover crop study at 25 sites showed a weak relationship of CO2 burst, POXC, soil protein and NO3-N with agronomic optimum N rate (AONR), with r values ranging from 0.00 to 0.48, suggesting these indicators may not be reliable predictors of N available in soil and corn yield. However, there was significant relationship between NO3-N at N sidedress time and relative yield (r = 0.65) at these long-term sites. In short-term cover crop study (Chapter 1), Presidedress nitrate test (PSNT) nitrate concentration was >15 mg kg-1 at 5 sites and in long term cover crop study (Chapter 2), 15 sites had nitrate concentration > 15 mg kg-1 indicating potential of N sidedressing reduction when compared to current pre-sidedress N test (PSNT) N recommendation in Virginia, which is currently only recommended for sites receiving manure or biosolids. A cover crop decomposition study at Kentland showed that hairy vetch had a faster decomposition rate (k = 0.0377 g g-1 d-1) than rye and vetch mix (k = 0.0292 g g-1 d-1) or cereal rye (0.0227 g g-1 d-1) with 0 N fertilizer and released more N than cereal rye and rye and vetch mix. The difference in C: N ratio (hairy vetch (9-11:1), cereal rye (31-46:1), rye and vetch mix (19-20:1)) may have affected decomposition rate and N release of cover crops. Hairy vetch released significant amounts of N within a month of incubation, with 103 kg N ha-1 in 2021 and 57 kg N ha-1 in 2022. Overall, this study showed that cover crops did not have a consistent or significant effect on soil health indicators in short term. However, cover crops improved CO2 burst at long term cover crop site compared to no-cover, control. Future studies should focus on understanding best methods of predicting N available to subsequent crop and conduct cover crop decomposition studies across the state with different cover crop species and their mixture. / Doctor of Philosophy / Increasing food production and fertilizer application especially nitrogen has degraded the soils capacity to provide nutrient to crops. Cover crops are crops planted after harvesting main crops like corn, soybean and cotton to protect soil from erosion and improve the soil's nutrient supply capacity. Planting cover crops in fall rather than leaving soil bare can be a best management practice to improve the soils and reduce the nitrogen loss to water bodies. The purpose of this study was to measure soil properties that shows how healthy the soil is, find the relation of soil properties with corn N requirement and corn yield, and estimate decomposition rate and nitrogen release after cover crop termination. Results showed that one year of cover crop versus no-cover crop had no effect on active carbon (permanganate oxidizable carbon, POXC), microbial respiration (CO2 burst). However, long term cover cropping increased CO2 burst. In long term cover cropping fields, nitrate concentration measured before N sidedress time (also called presidedress nitrate test, PSNT) was increased at 15 sites indicating these sites could reduce their N sidedressing. Cover crop decomposition study showed that decomposition and nitrogen release from hairy vetch was faster than cereal rye, and cereal rye and vetch mixture. Overall, planting cover crop showed did not improve in short term but planting cover crop for long term have potential to reduce the amount of nitrogen fertilizer need for corn, especially when legume cover crops are use.

Current interest in cover cropping is focused on enhancing ecosystem services beyond soil conservation. Cover crop (CC) species function uniquely in their effects on ecosystem services when grown in monoculture or mixtures. This research integrated field experiments and a literature synthesis to evaluate the role of cover crops in improving nitrogen (N) management and simultaneously providing multiple ecosystem services. Legume CC fertilized with poultry litter (PL) could replace 101 to 117 kg N ha-1 of fertilizer in corn (Zea mays L.) production. Rye (Secale cereale L.) CC fertilized with PL had a negligible effect on corn production. Biculture fertilizer equivalence ranged between -12 to +75 kg N ha-1. Fertilizer equivalence of legume-containing treatments increased across time. Without CC, fall-applied PL failed to supply N to corn. Ecosystem services of CC and PL illustrate complex species functions. Bicultures produced more total biomass than monocultures in year 1 but less than rye in year 2. Bicultures were as effective in suppressing weeds as rye, produced corn yield similar to legume, and by the second year had similar amounts of available soil N as the legume. Poultry litter effects and interspecific effects cover crop species biomass differed. Rye yield increased, while legume yield decreased slightly in biculture. Poultry litter increased legume N content and a decrease in legume C:N, while rye N content and C:N were unaffected. The synthesis corroborates that mixed and biculture cover crops yield more than the individual component species. Overyielding was transgressive in 60% of cases studied. Mixture effects varied by species: rye and brassica yield increased, while legume decreased in mixtures. The effect of mixed CC on crop yields varied by crop species and management practices, though generally crops increased 8 to 18% overall. This work can be applied to the design of complex CC and PL systems that optimize individual species functions to enhance ecosystem services. / Ph. D.

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.

<p></p><p>It is estimated that in the United States, agronomic weeds are responsible for about 50% of crop yield loss, costing nearly $27 billion each year. As interest in cover crops across the Midwest increases, so does the need to understand when to terminate cover crops for maximum weed control while still maintaining crop yield. Field experiments were conducted in 2017 and 2018 in Indiana to evaluate the effect of cover crop termination timings on weed control, and corn and soybean yield. Cereal rye (<i>Secale cereale </i>L.) and canola (<i>Brassica napus </i>L.) were subjected to early- or late- termination utilizing glyphosate-, saflufenacil- or glufosinate-based burndown herbicide programs. In corn, cereal rye and canola reduced early season weed biomass by 58 to 67% compared to fallow (no cover crop) plots. Cereal rye and canola reduced horseweed (<i>Erigeron canadensis </i>L.) and giant ragweed (<i>Ambrosia trifida </i>L.) emergence by 42 to 50% compared to fallow plots. Early- and late- terminated cereal rye reduced corn yields by 55 to 67% (5,173 to 7,116 kg ha^-1) compared to canola or fallow plots. In soybean, cereal rye and canola reduced early season weed biomass by 73 to 88% compared to fallow plots. Cereal rye and canola reduced horseweed emergence in 2017 and 2018 by 16 to 67 % compared to fallow plots. In 2017, both cover crop and termination timing influenced giant ragweed emergence. Early- and late- terminated cover crop plots reduced giant ragweed emergence by 50 to 76% compared to fallow plots. In 2018, cover crop termination timing influenced soybean yield. Late-terminated plots reduced yields by 48% compared to early-terminated plots. Results from this study suggest that cereal rye and canola planted at these rates can be effective for weed suppression prior to corn and soybeans, however, yield loss in both corn and soybean is expected. </p><p>Reports from Indiana in 2015 suggested that growers planting canola as a cover crop were experiencing difficulties when terminating with glyphosate prior to corn and soybean production. This suggests the utilization of inadequate herbicide programs, or perhaps a seed contamination event containing glyphosate resistant canola. Field experiments were conducted in 2016 and 2017 to determine the most effective herbicide treatment for terminating glyphosate resistant canola in Indiana, and to quantify how these herbicide programs influence corn yield. Canola was planted in early September and herbicide treatments were applied in the spring three weeks before corn planting. Visual ratings of control and above-ground biomass reduction were collected 21 days after treatment (DAT). The highest control of canola occurred following the application of paraquat + saflufenacil + 2,4-D or metribuzin, resulting in 88 to 94% control. These control ratings are supported by applications with paraquat + saflufenacil + 2,4-D or metribuzin resulting in 88 to 97% biomass reduction. Auxin herbicides alone provided very poor control, less than 41% at both locations. In general, saflufenacil-containing herbicide treatments provided the highest control of canola compared to mesotrione or atrazine. Herbicide treatments had no effect on corn grain yield.</p><br><p></p>