Department of Agricultural Chemistry, Soil Science and Biochemistry, College of Agriculture, Orissa University of Agriculture and Technology, Bhubaneswar, Orissa, 751003.
* USDA/ARS, University of Nebraska, Lincoln, NE, USA.
Field experiments were carried out in replicated microplots (1 m × 1 m) with rice (cv. Pathara) to study urea hydrolysis using several urea based N-fertilizer sources, viz. gypsum coated urea (GCU), urea nitrophosphate (UNP) (19-19-0), urea nitrophosphale (UNP) (27-9-0), urea super granule (USG), prilled urea (PU) + encapsulated calcium carbide (ECC) along with PU, FYM with no nitrogen (control). Urea tagged with 15N (10% a.e.) was also applied to rice grown in polyethylene enclosed microplots. Results indicated highly significant grain yield response due to all urea based N-jertilizers, among which usa and PU (applied in two splits) could be rated as the most efficient sources of N. Based on measured ammonia volatilization loss, NH2-N concentration in flood water and soil solution (following fertilizer application); urea hydrolysis was observed to be faster in the case of PU, usa, PU + ECC and UNP (19-19-0) than in the case of GCU and UNP (27-9-0) treatments. Based on the 15N tagged prilled urea experiment, it is observed that about 24 per cent of fertilizer nitrogen was utilized by the crop in closed system as compared to 18 per cent in naturalfree system. About 6–7 per cent of nitrogen got volatilized, 40–48 per cent of nitrogen remained in soil in complex form and 23 per cent of nitrogen was lost either through leaching and! or denitrification in the closed system.
Urea hydrolysis, ammonia volatilization, free system, closed system, soil solution, flood water
