WATER MANAGEMENT EFFECTS ON MINERALIZATION OF SOIL ORGANIC-MATTER ANDCORN RESIDUE

Water table control is being used on large areas of poorly drained Atl antic Coastal Plain soils during the winter to reduce N losses to surf ace waters. This study was conducted to determine the effect of water table depth (WTD) and control on N mineralization of added corn (Zea m ays L.) residue, Soil columns (15-cm-diam.) were extracted to 70-cm de pth from a Portsmouth loam (fine-loamy over sandy or sandy-skeletal, m ixed, thermic Typic Umbraquult), placed in polyvinyl chloride (PVC) wa ter table columns, and buried even with the surrounding soil surface, Labeled corn residue (18.01 atom % excess N-15) was incorporated in th e upper 15 cm of the PVC columns and WTDs of 0, 15, 30, and 45 cm main tained. Soil microsamples were taken over time for N analyses. After 2 09 d, approximately 8 to 13% of the inorganic N came from the N added as plant residue, even though the added N was only 1.1% of the total s oil N. Although the 0- and 15-cm WTD treatments accumulated little (NO 3)-N-15-N, they contained appreciable (15)NR(4)-N. In contrast, the 30 - and 45-cm WTD treatments ac cumulated primarily (NO3)-N-15-N as inor ganic N accumulation increased with time and rising soil temperatures. It was concluded that WTD control could be used during the winter to promote denitrification of available NO3-N and thus to minimize NO3-N lost to drainage water.