Coupling winter small grain cover crops (CC) with manure (M) application may increase retention of manure nitrogen (N) in corn ( Zea mays L.), -soybean [ Glycine max (L.) Merr], cropping systems. The objective of this research was to quantify soil N changes after application of liquid swine M ( Sus scrofa L.) at target N rates of 112, 224, and 336 kg N ha -1 with and without a CC. A winter rye ( Secale cereale L.)-oat ( Avena sativa L.) CC was established prior to fall M injection. Surface soil (0-20 cm) inorganic N concentrations were quantified every week for up to 6 weeks after M application in 2005 and 2006. Soil profile (0-120 cm in 5, 20-cm depth increments) inorganic N, total N, total organic carbon and bulk density were quantified for each depth increment in the fall before M application and before the CC was killed the following spring. Surface soil inorganic N on the day of application averaged 318 mg N kg -1soil in 2005 and 186 mg N kg -1soil in 2006 and stabilized at 150 mg N kg -1soil in both years by mid-November. Surface soil NO 3-N concentrations in the M band were more than 30 times higher in the fall of 2005 than in 2006. The CC reduced surface soil NO 3-N concentrations after manure application by 32% and 67% in mid- November 2005 and 2006, respectively. Manure applied at 224 kg N ha -1 without a CC had significantly more soil profile inorganic-N (480 kg N ha -1) in the spring after M application than manured soils with a CC for the 112 (298 kg N ha -1) and 224 (281 kg N ha -1) N rates, and equivalent inorganic N to the 336 (433 kg N ha -1) N rate. These results quantify the potential for cover crops to enhance manure N retention and reduce N leaching potential in farming systems utilizing manure.
