Winter and growing season nitrogen mineralization from fall-applied composted or stockpiled solid dairy manure

Adequate characterization of nitrogen (N) mineralization with time from manure and other organic sources is needed to maximize manure N use efficiency, decrease producer costs, and protect groundwater quality. The objective of our 2-year field study at Parma, ID, was to quantify in situ N mineralization with time as affected by a one-time fall application of solid dairy manure, either composted or stockpiled. The experiment included five treatments: a non-N fertilized control, two first-year rates of stockpiled solid dairy manure (21.9 and 43.8 Mg ha−1, dry wt.) and two rates (53.1 and 106.1 Mg ha−1, dry wt.) of composted dairy manure (hereafter termed compost). Net N mineralized (mineralization less immobilization) was determined to a depth of 0.3 m by repeatedly measuring soil inorganic N (NH4-N + NO3-N) concentrations in buried polyethylene bags. Overwinter mineralization was measured between amendment incorporation in fall and sugarbeet (Beta vulgaris L.) planting the following spring. In-season mineralization was measured in situ for seven consecutive incubation periods during the c. 220-day growing season for furrow-irrigated sugarbeet. Net N mineralized often varied among amendments and from year to year through mid-season, likely due to seasonal variation in soil temperature, annual differences in amendment properties, and other factors. In early spring 2003 after a warmer-than-normal winter, immobilization exceeded mineralization, regardless of treatment. In-season net N mineralized peaked between mid-August and early September (DOYs 230–251) each year, regardless of treatment. Annual (c. 11-month) net N mineralized in 2003 averaged 52 kg N ha−1, similar among treatments. In 2004, annual net N mineralized was similar between rates within amendments and averaged 250 kg N ha−1 where manure treated, 150 kg N ha−1 where compost treated, and 106 kg N ha−1 where untreated. On average in 2004, 31 % of compost’s annual net N mineralized occurred before the growing season and 69 % during the season while essentially all of manure’s net N mineralized occurred during the season. None of the amendments’ total N was, in net, mineralized in 2003 but in 2004 on average, 2 % of compost’s and 16 % of manure’s total N was mineralized, similar between rates within amendments. When estimating annual net N mineralized from fall-applied organic amendments, one must account for abnormal temperatures, including those overwinter.