0023-6152

AA00697606

4520

Unrefereed

0023-6152

AA00697606

Nitrogen efficiency of two methods of application of urea at topdressing of paddy rice (Oryza sativa L. cv. Koshihikari) before panicle initiation stage (BPIS) as well as recovery of basally applied nitrogen and topdressed nitrogen BPIS were studied in a pot experiment. Three N rates (200 (N200), 400(N400) and 600 (N600) mg kg[-1] soil) and equal P[2]O[5] and K[2]O rates (150mg kg[-1] soil) were applied. Topdressing BPIS was made by broadcasting [15]N-labeled urea and by injection of [15]N-labeled urea only for basal application was used. Concentration of the ammonium in leaching water varied from 45mg NH[4-]N L[-1] (N200) to 192 mg NH[4-]N L[-1] (N600) one week after transplanting date (TD) of rice and dropped to zero for about a month. The amount of urea determined a week after TD was 3, 9 and 13mg urea-N per pot at the three N rates (higher N rate led to higher leaching of K) and plant growth. No positive effect was found of the injection method of urea application into the soil on the grain yield and the nitrogen accumulation in the plants in comparison with the broadcast method of urea application BPIS. The differences in [15]N recovery among studied N rates were less with injected urea BPIS where [15]N recovery was from 68% at the lowest N rate to 75% at the highest rate, while that was from 57 to 79%, respectively with broadcast urea BPIS. The recovery of basally applied nitrogen was less than topdressed nitrogen and renged from 39 to 44%. There was no significant difference between methods of N application BPIS on the aooarent nitrogen recovery, which varied between 58 and 68%.