Transformation of nitrogen in urea and DAP amended soils

Nitrogen (N) and phosphorus (P) transformation pattern in urea and diammonium phosphate (DAP) amended alluvial, calcareous and red soils of Bangladesh were studied. Nitrogen (4) 0, 100 and 200 pg g soil was added from urea or DAP. Ammonification and nitrification were monitored over 90 days of incubation period maintaining 30% moisture at room temperature. Depending on soil types and N sources and doses, transformation of N varied significantly over the incubation period. The rate of ammonification increased rapidly, reached the maximum level between 6 and 10 days, and almost disappeared within 30 days. On the other hand, the nitrification rate decreased temporarily, then it showed increasing trend and reached the maximum level within 30 to 40 days and almost disappeared within 50 days. Among the soils, the highest rate of N mineralization was observed in alluvial soil and the lowest in red soil. Although 200 pg g-1 N amended soils produced higher amount of NF14+-N and NO3--N than 100 pg g-1 N amendment, relative performance of 100 pg g N amended soil was better than 200 pg g-1 N amendment. Between two fertilizers, urea showed a faster and higher rate of mineralization while DAP had a steady state and relatively slower rate of mineralization for the incubation period