EFFECT OF SEWAGE-SLUDGE AND AMMONIUM-NITRATE ON WHEAT YIELD AND SOIL-PROFILE INORGANIC NITROGEN ACCUMULATION

The beneficial effect of sewage sludge in crop production has been dem onstrated, but there is concern regarding its contribution to nitrate (NO3) leaching. The objectives of this study were to compare nitrogen (N) rates of sewage sludge and ammonium nitrate (NH4NO3) on soil profi le (0-180 cm), inorganic N [ammonium nitrate (NH4-N) and nitrate nitro gen (NO3-N)] accumulation, yield, and N uptake in winter wheat (Tritic um aestivum L.). One field experiment was established in 1993 that eva luated six N rates (0 to 540 kg . ha(-1). yr(-1)) as dry anaerobically digested sewage sludge and ammonium nitrate. Lime application in 1993 (4.48 Mg ha(-1)) with 540 kg N ha(-1). yr(-1) was also evaluated. A l aboratory incubation study was included to simulate N mineralization f rom sewage sludge applied at rates of 45, 180, and 540 kg N ha(-1). yr (-1). Treatments did not affect surface soil (0-30 cm) pH, organic car bon (C), and total N following the first (1994) and second (1995) harv est. Soil profile inorganic N accumulation increased when greater than or equal to 270 kg N ha(-1) was applied as ammonium nitrate. Less soi l profile inorganic N accumulation was detected when lime was applied. In general, wheat yields and N uptake increased linearly with applied N as sewage sludge, while wheat yields and N uptake peaked at 270 kg N ha(-1) when N was applied as ammonium nitrate. Lime did not affect y ields or N uptake. Fertilizer N immobilization was expected to be high at this site where wheat was produced for the first time in over 10 y ears (previously in native bermudagrass). Estimated N use efficiency u sing sewage sludge in grain production was 20% (average of two harvest s) compared to ammonium nitrate. Estimated plant N recovery was 17% fo r sewage sludge and 27% for ammonium nitrate.