Department of Soil Science and Agricultural Chemistry, Orissa University of Agriculture and Technology, Bhubaneswar, Orissa, 751003
Present address: 1Asst. Soil Conservation Officer, Directorate of Soil Conservation, Government of Orissa
The efficiency of urea super granules (USG) for increasing rice grain yield in flooded condition is well established. But the transport mechanism and transformation process of USG-N in submerged rice soil is not very well understood. A field experiment was conducted during 1995 to study the transport of N species originating from 1g urea super granules (USG) point-placed in the rice root zone at 0.025 and 0.05 m soil depth. Velocity of urea-N at 0.20 m soil depth was higher than that of NH4+-N. The velocity of water was lower than urea-N and NH4+-N. Nitrogen in the form of urea-N and NH4+-N to the extent of 20–55% of applied USG-N was detected in soil solution collected at 0.20 m soil depth. Downward movement of NH4+-N was higher than upward diffusion from the point of placement of USG. No NO3−-N was detected in the soil solution. Manual placement of USG at 0.05 m soil depth increased both grain and straw yield significantly over surface application of prilled urea at same N dose. On the other hand, grain yield due to mechanical application of USG was at par with that of yield due to the application of USG manually. Mechanical placement of USG at 0.05 m soil depth in flooded rice soil will be cost-effective and economical without much reduction in yield.
USG, urea hydrolysis, leaching, rice, flooded soil
