Overwinter and in-Season Nitrogen Mineralization for Sugarbeet from Solid or Composted 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 two-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.  We studied four replications of five treatments: a non-N fertilized control, two rates of stockpiled solid manure (21.9 and 43.8 Mg ha^-1, dry wt.) from dairy cattle (Bos taurus) replacement heifers, and two rates (53.1 and 106.1 Mg ha^-1, dry wt.) of composted dairy cattle manure.  Net N mineralization, calculated as 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-d growing season for furrow-irrigated sugarbeet.  Net N mineralization often varied among amendments and from year to year through mid-season, likely due to seasonal variation in temperature and other factors.  In early spring 2003 after a warmer-than-normal winter, immobilization exceeded mineralization, regardless of treatment.  In-season net N mineralization peaked between mid-August and early September (DOYs 230 to 251) each year, regardless of treatment.  Annual (c. 11-mo) net N mineralization in 2003 averaged 52 kg N ha^-1, similar among all treatments.  In 2004, annual net N mineralization averaged 250 kg N ha^-1 for manure, 150 kg N ha^-1 for compost, similar between rates within amendments, and 106 kg N ha^-1 where untreated.  On average in 2004, 31% of compost’s annual net N mineralization occurred before the growing season and 69% during the season while essentially all of manure’s occurred during the season.  Of the amendments’ total N, none was mineralized in 2003 while in 2004 on average, 2% of compost's and 16% of manure's was mineralized, similar between rates within amendments.  Abnormal temperatures, including those overwinter, must be accounted for when, the following spring, one estimates annual net N mineralization from fall-applied organic amendments.