Thesis (M.S.)--California Polytechnic State University, 2009. / Title from PDF title page; viewed on December 2, 2009. Major professor: Brent G. Hallock, Ph.D. "Presented to the faculty of California Polytechnic State University, San Luis Obispo." "In partial fulfillment of the requirements for the degree [of] Master of Science in Agriculture with specialization in Soil Science." "November 2009." Includes bibliographical references (p. 67-71). Also available on microfiche.

The effect of cover crops on N and weed dynamics was assessed within a pea (Pisum sativum L.) – cover crop – sweet corn (Zea mays L.) rotation. Cover crops of oat (Avena sativa L.), perennial rye (rye) (Secale cereale L.), oilseed radish (OSR) (Raphanus sativus L. var. oleoferus Metzg Stokes), and OSR plus perennial rye (OSR+rye) increased plant available N (PAN) over the cover crop growing season compared to the no cover control at the Bothwell site only. However, at neither site did cover crops result in increased PAN for the sweet corn, indicating that these cover crops will not reduce required N fertilizer applications. Also, cover crops posed neither an increased or decreased need for weed management during sweet corn production. However, OSR may be useful in pesticide reduced programs due to its potential ability to reduce fall herbicide applications, provided it does not set viable seed.

The use of high N fertilizer in sweet corn (Zea mays L.) and wheat (Triticum aestivium L.) production often results in leaching losses and contamination of ground water. Cover crops planted after harvest of sweet corn and wheat may reduce residual soil NO$ sp- sb3$-N levels by crop N uptake and subsequently minimize NO$ sp- sb3$-N content in gravitational water. Field experiments were conducted on a Ste. Rosalie heavy clay (Humic Gleysol) and a St. Bernard sandy clay loam (Melanic Brunisol) to determine the contribution of the six cover crops to nutrient uptake, subsequent N release, leaching losses, denitrification rates and soil properties such as aggregate stability, organic matter. The cover crops were red clover (Trifolium pratense L.), crimson clover (Trifolium incarnatum L.), forage radish (Raphanus sativus L.), canola (Brassica rapa L.), barley (Hordeum vulgare L.), annual rye grass (Lolium multiflorum L.). Three replicates were used in a split plot arrangement of a randomized complete block experiment. Sweet corn and wheat were grown at three fertilizer N rates, 0-75-150 kg N ha$ sp{-1}$ for sweet corn and 0-45-90 kg N ha$ sp{-1}$ for wheat. Cover crop of forage radish, canola and barley were more effective at absorption or soil N than rye grass and clover species at all sample times. Levels of soluble N in the soil were reduced with cover crop in the off-season. Cover crop plots had higher NO$ sp- sb3$-N levels than control plots in the spring, indicating net mineralization and nitrification. Gravitational water NO$ sp- sb3$-N contents were higher in the control plots relative to cover crop plots at both sites. Therefore growing cover crops after harvest of sweet corn and wheat can reduce residual NO$ sb3$-N level in the soil and thus restrict ground water contamination with fertilizer N.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Vita. Includes bibliographic references.

Thesis (M.S.) in Plant, Soil and Environmental Sciences--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 88-93).

Thesis--Auburn University, 2008. / Abstract. Vita. Includes bibliographical references (p. 54-59).

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 89-96). Also available on the World Wide Web.

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Includes bibliographical references (leaves 159-167). Also available on the World Wide Web.

AN ABSTRACT OF THE THESIS OF Taylor J. Sievers, for the Master of Science degree in Plant, Soil, and Agricultural Systems, presented on May 13, 2016, at Southern Illinois University Carbondale. TITLE: COVER CROP CHARACTERISITICS AND IMPACTS ON AGRONOMIC SYSTEMS IN SOUTHERN ILLINOIS MAJOR PROFESSOR: Dr. Rachel L. Cook Midwestern farmers face the dual challenge of increasing crop production while reducing environmental impacts. Best management practices to decrease nutrient and soil loss in agronomic systems has fueled the resurgence of the cover cropping practice, but many growers are uncertain about the effects that different cover crop species may have in their fields or how combinations of tillage and cover crops may influence yields or soil characteristics. Different cover crop characteristics, such as above and belowground biomass production, nitrogen content, and decomposition may affect both soils and crop yields. Field experiments were conducted across two sites in southern Illinois from 2013 to 2015 to study characteristics of cover crops and the impact of cover crops and tillage on soils, nutrient availability, and agronomic field crop performance. Specifically, these studies 1) determine the effects of cover crops on soil nitrogen, 2) quantify above and belowground biomass production of cover crops, 3) quantify the grain yield and belowground biomass of the following crops of corn (Zea mays L.) and soybeans (Glycine max L. Merr.), and 4) evaluate cover crop decomposition and nutrient release of a leguminous and non-leguminous species. In both field sites, Hairy vetch (Vicia villosa Roth) treatments produced the most biomass and accumulated the most nitrogen of all cover crop treatments. Cover crop establishment was a problem for the 2014−2015 field season. Cover crops, for the most part, did not have an influence on corn or soybean grain yields, except that corn following Hairy vetch treatments tended to be higher in grain yields than corn following Annual ryegrass treatments. Soybeans following Annual ryegrass treatments tended to be higher in grain yield than soybeans following Canola treatments. Root biomass production was higher for cover cropped plots than non-cover cropped plots (weed root biomass), and corn or soybean root biomass was more affected by tillage practices rather than the main effect of cover crop. Tilled treatments were typically higher in soil nitrate and total inorganic nitrogen compared to No-till treatments, and Annual ryegrass treatments were consistently lower in soil nitrogen compared to other cover crop treatments. Hairy vetch and cereal rye (Secale cereale L.) decomposition and nutrient release was monitored over a 16 week period, with litterbag and intact root core collections at 2, 4, 6, 8, 12, and 16 weeks. Decomposition and nitrogen release data were fit to a single exponential decay model with an asymptote. Cereal rye aboveground (k = 0.14) and belowground (k = 0.19) biomass decomposed more gradually compared to hairy vetch aboveground (k = 0.45) and belowground (k = 0.68) biomass. The same trend developed for nitrogen release with cereal rye aboveground (k = 0.07) and belowground (k = 0.19) biomass releasing nitrogen slower and more gradually compared to hairy vetch aboveground (k = 0.61) and belowground (k = 0.61) biomass. Most of the hairy vetch nitrogen was released around Week 2, but the corn crop did not reach the V6 growth stage until Week 8, therefore cover crop nitrogen release and cash crop uptake may have not been synchronized. Plant Root Simulator™ ion exchange resin membrane probes also captured significantly more nitrogen in hairy vetch plots compared to cereal rye plots at weeks 2, 4, 6, 8, and 12, which indicates that hairy vetch could increase the readily plant available total nitrogen (nitrate + ammonium) in the soil throughout the bulk of cover crop decomposition. Farmers should decrease the time between cover crop termination and cash crop planting in order to increase the likelihood of crop synchrony. This research will help farmers develop better management practices regarding inclusion of cover crops into traditional agronomic production systems.