The pairing of cover crops with spring application of nitrogen has shown improved nitrogen efficiency in corn production systems. However, studies have shown that only 50% of central Illinois farmers practice spring application of nitrogen. Furthermore, the literature demonstrates that in years with above average rainfall, fall applied N management systems are more susceptible to N loading relative to spring systems. Therefore, the objective of this research was to determine the efficacy of winter cover crops to impact the distribution of soil inorganic N following fall applied anhydrous ammonium. The experimental site is located at the Illinois State University Research and Teaching Farm in Lexington, IL. The treatments consisted of a control, daikon radish, cereal rye and a cereal rye/daikon radish mixture. All treatments received a fall application of 200 kg N ha-1 in the form of anhydrous ammonia. Soil samples were collected in the spring at four separate depths and were analyzed for inorganic N. At the 0-5cm depth, we determined that tillage radish resulted in 18% greater soil NO3- relative to the control. In the environmental depth of 20-80cm, we observed that fall applying N into a living cover crop resulted in 35% (cereal rye) and 22% (daikon radish) less soil NO3- when compared to the control. In 2014 and 2015, each treatment was further divided into three nitrogen rate subplots: 200, 145 and 90 kg N ha-1. However, no obvious trend within the rate applied (90, 145 and 200 kg ha-1) was observed. After four consecutive years of established cover crops, corn uptake and yield data was collected. On average the addition of daikon radish at 200 kg N ha-1 increased total crop uptake by 20%; while the inclusion of cereal rye despite application rate significantly (P= 0.0021) increased total N at R6. Consequently, sampling at harvest (2014) demonstrated the capacity of the cover crops (cereal rye, P= 0.0323) despite rate to increase the crop yielding potential 3-6%. Over a four year period, winter cover crops reduced nitrate leaching and stabilized a greater concentration of soil NO3- in the agronomic depths following fall applied N, relative to the control. The results of this study also suggest that cover crop inclusion into a fall applied system has the potential to advance nitrogen use efficiency, yield and profitability.

Nitrate loss studies in Midwestern tile-drained fields have found that fall applied nitrogen (N) resulted in elevated nitrate concentrations in tile water during both the corn and soybean year of a 2 year rotation. The effectiveness of cover crops to reduce nitrate leaching when N is spring applied has been well demonstrated, however there is a dearth of knowledge on the ability of cover crops to reduce nitrate leaching in a system where N is fall applied. Thus, the objectives of this research were to (i) investigate the efficacy of winter cover crops to reduce nitrate leaching from fall applied nitrogen and (ii) investigate the impact of cover crops on N mineralization in the spring before planting main crops. The experimental site was located at the Illinois State University Research and Teaching Farm in Lexington, IL. All treatments received fall nitrogen at a rate of 200 kg ha-1 into standing cereal rye, tillage radish and control (no cover crop). Cover crops were sampled and analyzed for total nitrogen to calculate N-uptake. Soil samples were collected during the fall and spring months and analyzed for nitrate and ammonium. Despite variable weather conditions, both cover crop treatments demonstrated the potential to reduce nitrate leaching compared to a no cover crop control. The tillage radish treatment resulted in consistently greater soil inorganic N compared to other treatment immediately before planting. In contrast, cereal rye residue slowly decomposed over time and resulted in a slower rate of mineralization. Therefore, both cover crop species increased the efficiency of fall applied N by reducing nitrate leaching and increasing inorganic N at the soil surface.

"Many farmers apply manure in the fall (autumn season), but without an actively growing crop in the ground, the nitrogen (N) in the manure is susceptible to over-winter losses. Periods of freeze-thaw cycling can exacerbate N losses by stimulating soil microbes to transform reactive substrates like soil mineral N into nitrous oxide (N2O), a potent greenhouse gas. The uptake of reactive N from fall-applied manure by a fall-sown cover crop may reduce over-winter N losses. The objective of my research was to investigate the effect of combining fall manure application with cover cropping on soil N dynamics over winter and during periods of freeze-thaw cycling under field and laboratory conditions. I also examined the relationship between N2O production and reactive soil substrate concentrations. The field experiment was a full factorial in a randomized complete block design with three manure treatments (none, liquid, solid) and four cover crop types (no cover crop, 100% ryegrass [Lolium multiflorum Lam.], a 75% ryegrass/25% hairy vetch [Vicia villosa Roth] mixture and a 50% ryegrass/50% vetch mixture). The experiment was established at two field sites in Québec, Canada. A partial N mass balance (g N m-2) was calculated in fall (sum of the fall soil N stock to 0.15 m depth, N in fall-applied manure, and N in cover crop biomass) and in spring (sum of the spring soil N stock to 0.15 m depth and N in the winter-killed cover crop) for each treatment combination. After terminating the cover crop, spring wheat (Triticum aestivum L.) was planted, and each main plot was split into two subplots that received either 100 kg N ha-1 urea fertilizer or no fertilizer. Wheat samples were taken at tillering, flowering, and maturity to determine N content. Final yield was also measured. Cover crops were not effective at retaining manure N (≤7% uptake) and there was no difference in the fall and spring N balance among the manure and non-manure plots. Residual N was not supplied from fall-applied manure to the spring wheat in the next growing season, and average wheat yields were 11–14% less in the subplots that received no spring N fertilizer than those that received 100 kg N ha-1. In the laboratory, pots with 280–285 g soil received four N fertilizer treatments (none, liquid manure, solid manure, urea), with or without an annual ryegrass cover crop. The pots were exposed to 0, 1, 2, or 3 simulated freeze-thaw cycles (FTCs) at -4 to +4°C. The N2O production was measured at 0, 3, 6 and 9 h for each FTC, then pots were destructively sampled to determine the soil mineral N concentration. There was no difference in N2O production among the treatment combinations across all FTCs, but the pots that received urea or liquid manure had the highest soil mineral N concentration. The cover crop had minimal effect on the soil mineral N concentration. Soil mineral N explained approximately 14% of the variation in N2O production. Pots that underwent FTCs had a remarkable 937–1000% increase in N2O production compared to unfrozen pots. This suggests that N2O-producing microbial activity occurred in the frozen soils at -4oC, causing N2O to accumulate under ice and be released when the soils thawed at 4oC, mostly within the first 3 h. The results of both the field and laboratory studies suggests that microbial N transformations do not stop during the winter months, leading to substantial losses of N in fertilized soils during the non-growing season in cold humid temperate regions"--

Cover crops slow erosion, improve soil, smother weeds, enhance nutrient and moisture availability, help control many pests and bring a host of other benefits to your farm. At the same time, they can reduce costs, increase profits and even create new sources of income. You¿ll reap dividends on your cover crop investments for years, since their benefits accumulate over the long term. This book will help you find which ones are right for you. Captures farmer and other research results from the past ten years. The authors verified the info. from the 2nd ed., added new results and updated farmer profiles and research data, and added 2 chap. Includes maps and charts, detailed narratives about individual cover crop species, and chap. about aspects of cover cropping.

Leguminous cover crops systems have been envisaged as a critical component of sustainable agriculture due to their potential to increase soil productivity through cycling of carbon (C) and nitrogen (N) in agricultural systems. The objectives of this study were to evaluate the performance of leguminous summer cover crops; cowpea [Vigna unguiculata (L.) Walp.], pigeon pea [Cajanus cajan (L.) Millsp], sunn hemp (Crotalaria juncea L.) and double-cropped grain crops; grain sorghum [Sorghum bicolor (L.) Moench] and soybean [Glycine max (L.) Merr.] after winter wheat (Triticum aestivum L.) and to determine the effects of these crops and varying N rates in the cropping system on nitrous oxide (N2O) emissions, growth and yield of succeeding grain sorghum and maize (Zea mays L.) crop, soil aggregation, aggregate-associated C, and N. Field and laboratory studies were conducted for two years. The cover crops and double-cropped grain crops were planted immediately after winter wheat harvest. The cover crops were terminated at the beginning of flowering. Nitrogen fertilizer (urea 46% N) rates of 0, 45, 90, 135, and 180 kg N ha−1 were applied to grain sorghum or maize in fallow plots. Pigeon pea and grain sorghum had more C accumulation than cowpea, sunn hemp and double-cropped soybean. Pigeon pea and cowpea had more N uptake than sunn hemp and the double-cropped grain crops. Fallow with N fertilizer application produced significantly greater N2O emissions than all the cover crops systems. Nitrous oxide emissions were relatively similar in the various cover crop systems and fallow with 0 kg N ha−1. Grain yield of sorghum and maize in all the cover crop and double cropped soybean systems was similar to that in the fallow with 45 kg N ha−1. Both grain sorghum and maize in the double-cropped soybean system and fallow with 90 kg N ha−1 or 135 kg N ha−1 gave profitable economic net returns over the years. The double-cropped grain sorghum system increased aggregate-associated C and whole soil total C, and all the cover crop and the double-cropped soybean systems increased aggregate-associated N and soil N pools. Inclusion of leguminous cover crops without N fertilizer application reduced N2O emissions and provided additional C accumulation and N uptake, contributing to increased grain yield of the following cereal grain crop.

Review of the principles and management implications related to nitrogen in the soil-plant-water system.