Field experiments were conducted to evaluate cover crop interseeding time and species effect on sugarbeet production during 2018 and 2019 growing seasons. Cover crops were first interseeded in June and second interseeding was done in late June or early July. Four cover crops species, Austrian pea (Pisum sativum L.), winter rye (Secale cereale L.), winter camelina [Camelina sativa (L.) Crantz], and brown mustard (Brassica juncea L.), were examined. First interseeding resulted in significantly higher cover crop biomass than second interseeding. In 2018, the highest recoverable sugar yield was observed with pea (13.9 Mg ha-1) and camelina (6.6 Mg ha-1) first-interseeded, at Ada and Downer, MN, respectively. In 2019, camelina (11.2 Mg ha-1) at Ada, MN, and pea (12.4 Mg ha-1) at Prosper, ND both second-interseeded, had the highest recoverable sugar yield. Cover crops had no negative impacts on sugarbeet, but the selection of species and planting time are critical.

Cover crops are typically sown between cash crops and can suppress weed emergence and growth. If cover crops are sown after cash crop harvest the system is left susceptible to weed emergence while they establish. Interseeding cover crops into a standing cash crop may limit this bare period by allowing cover crops to become established, go into dormancy, and then revive around cash crop senescence. Studies were conducted in Princeton and Lexington, KY, to determine (i) which corn pre-emergent herbicides and mixtures of herbicide active ingredients commonly used by Kentucky growers would impact interseeded cover crop density and biomass, (ii) which grass entries that are adapted to Kentucky would be best to interseed in corn, and (iii) if interseeded cover crops would suppress weeds similar to a cover crop planted after cash crop harvest. There were few reductions in interseeded cover crop density and biomass from the pre-emergent herbicides tested. Among the entries interseeded in four site-years, the tall fescue pre-cultivars generally performed the best but none were consistently able to survive the summer when interseeded into corn. Compared to a cereal rye cover crop seeded after corn harvest, interseeded cover crops produced less biomass and therefore suppressed fewer weeds.

Interseeding legumes in native warm-season grasses (NWSG) may improve the nutritive value of the stand, result in more consistent forage availability throughout the growing season, and increase forage yield. These benefits are often not realized due to difficulties in establishing legumes in existing NWSG stands. The objective of this study was to investigate the effect of planting method of legume interseeding, timing of legume interseeding, and the efficacy of burning plant residue on legume establishment in NWSG. Two forage legumes, 'Alice' white clover (Trifolium repens L.) and 'Freedom HR' red clover (Trifolium pratense L.), were interseeded into mixed 'Niagara' big bluestem (Andropogon gerardii Vitman), 'GA Ecotype' Indiangrass (Sorghastrum nutans Nash), and 'Camper' little bluestem (Schizachyrium scoparium) pasture in 2022 and 2023 at the Southern Piedmont AREC in Blackstone, Virginia. Planting method at three levels (no-till drill, broadcast, and non-planted control) were evaluated at three planting timing levels (fall planting, winter planting, and winter planting with burned residue). Among the treatment combinations, burned plots that were drilled resulted with the greatest spring clover count of 236 plants m-2, followed by winter drill (146 plants m-2) and burn broadcast (133 plants m-2). All fall plantings and all control plots were similar with a mean of 21 plants m-2. As a result of greater initial clover emergence, plots that were burned or seeded in the winter had greater clover content throughout the experiment; burned and drilled plots had over 90% clover ground cover throughout the second year. Domination of plots by clover in the second year caused yields and the proportion of NWSG in the stand to decline, with burned plots yielding 5,757 kg ha-1 compared to a winter-fall mean of 7,429 kg ha-1. Plots with greater clover content were able to sustain higher crude protein content and lower neutral detergent fiber content in both the establishment year and the second year. Though interseeding legumes benefitted nutritive values, these results suggest that red clover may be incompatible with the NWSG evaluated. Burned plots were especially affected by excessive competition. Further research is needed to evaluate forage legume species which complement NWSG in mixture rather than compete with them. / Master of Science / Interseeding legumes in native warm-season grasses (NWSG) may improve the nutritive value of the stand, result in more consistent forage availability throughout the growing season, and increase forage yield. These benefits are often not realized due to difficulties in establishing legumes in existing NWSG stands. The objective of this study was to investigate the effect of planting method of legume interseeding, timing of legume interseeding, and the efficacy of burning residue on legume establishment in NWSG. Two forage legumes, 'Alice' white clover (Trifolium repens L.) and 'Freedom HR' red clover (Trifolium pratense L.), were interseeded into mixed 'Niagara' big bluestem (Andropogon gerardii Vitman), 'GA Ecotype' Indiangrass (Sorghastrum nutans Nash), and 'Camper' little bluestem (Schizachyrium scoparium) pasture in 2022 and 2023 at the Southern Piedmont AREC in Blackstone, Virginia. Planting method at three levels (no-till drill, broadcast, and non-planted control) were evaluated at three planting timing levels (fall planting, winter planting, and winter planting with burned residue). Among the treatment combinations, burned and drilled plots produced more clover plants in spring at 236 plants m-2, followed by winter drill (146 plants m-2) and burn broadcast (133 plants m-2). All fall plantings and all control plots were similar with a mean of 21 plants m-2. As a result of greater initial clover emergence, plots that were burned or seeded in the winter had greater clover content throughout the experiment; burned and drilled plots had over 90% clover ground cover throughout the second year. Domination of plots by clover in the second year caused yields and the proportion of NWSG in the stand to decline, with burned plots yielding 5,757 kg ha-1 compared to a winter-fall mean of 7,429 kg ha-1. Plots with greater clover content were able to sustain higher crude protein content and lower neutral detergent fiber content in both the establishment year and the second year. Though interseeding legumes benefitted nutritive values, these results suggest that red clover may be incompatible with the NWSG which were evaluated. Burned plots were especially affected by excessive competition. Further research is needed to evaluate forage legume species which complement NWSG in mixture rather than compete with them.

Agroecosystem sustainability as a framework for agriculture production systems requires attention to detail to multiple facets of the underlying production system. Production systems must achieve optimal cash crop yields while remaining profitable. Likewise, production practices must be tailored to reduce its environmental footprint. Identifying practices that encourage improved soil physical and chemical properties while maintaining yields have largely been challenging. Cover crops have been an integral part of the conversation regarding practices that can generally improve those properties of soil responsible for overall soil health. Use of winter cereal cover crops (WCCC’s) have shown promise as a tool for reducing soil and nutrient run-off, thereby reducing nitrogen (N) and phosphorus (P) nonpoint source pollution in the Upper Mississippi River Basin (UMRB). However, corn-cash crop yield penalties are often incurred following the use of WCCC’s such as winter cereal rye (Secale cereal) (WCR), as N is immobilized by cover crop residues in the decomposition processes. Additionally, traditional planting methods of cover crops have resulted in reductions of harvestable populations of corn and soybeans. These problems indicate a necessity for novel cover crop planting methods that reduce the consequential outcomes of implementing traditional cover crop practices. Using a method called “Skipping the corn row” (STCR), otherwise identified as “precision planted” cover crops, we aimed to reduce the cash crop yield-limiting interactions of cover crop residues within the cash crop row. We hypothesized that removing cover crop biomass from the subsequently planted cash crop row (chapter 1) could minimize N immobilization by residues, thereby increasing our subsequent yield potential and economic optimum return to N (EORN). In novel cover crop planting methods preceding soybeans (chapter 3), our hypothesis indicated that mixtures of WCR and crimson clover (Trifolium incarnatum) would impact biomass accumulation of weed communities, while novel measures that allowed for reduced seeding rates would permit competitive soybean yields while reducing input costs for cover crop seed. Chapter 2 focused on interseeding mixtures of WCR and crimson clover, where we hypothesized that residual rates would marginally impact percent cover of WCR and crimson clover mixtures. Our results indicated, in chapter one, that reducing seeding rate by using STCR planting method did indeed drive seed cost savings while improving yield and EORN in comparison to a traditionally planted cover crop. Our results in chapter 3 also indicated reduced seeding rates found in novel planting methods improved the on-farm economics of using cover crops while maintaining healthy soybean yields. Lower-than-average rainfall accumulations later in the growing season coupled with cover crop residues likely influenced soil moisture retention, benefiting the cash crop during the dry spell, helping maintain yields. Interseeding methods, as studied in chapter 2, did not show any significant impact on corn grain yield or yield components. Subsequently, half- and full-rate residual herbicides did not impact percent cover of cover crops. However, use of residual herbicides should be consistent with all herbicide labels and laws, and producers should use label-recommended amounts to maintain maximum efficacy of herbicides and to prevent resistant weed populations. Also, interseeded cover crops failed to successfully establish, resulting in minimal cover crop biomass in later sampling dates.