Research within the coordinated programme on the use of isotopes in rice production studies

In the wet season experiment, water management practices (continuous flooding versus two days' drainage before top dressing of N-fertilizer) had no significant effect on the yield of rice plant, nor were any significant differences observed for the sources of N tested. Local rice variety Patnai produced greater yield than IR.22. There were no varietal differences in fertilizer-N absorption. The recovery of fertilizer-N by the plant was affected by the time of N application. Overall utilization from ammonium sulfate and urea was 5.6 and 5.7% respectively, for IR.22 and 7.3 and 7.3% for Patnai. Rice plants, especially IR.22, did not perform well in the acid sulfate soils. Continuous flooding was found to be more efficient than mid-term drainage in the conversion of fertilizer-N into grain protein. Both IR.22 and Patnai absorbed more soil-N. In dry season experiments (1971) water management was seen to have no effect on grain production. Application of N-fertilizer did not increase paddy yield significantly. Here, too, ammonium sulfate proved better than urea. Water management did affect the percentage and yield of fertilizer-derived N. Its recovery was affected by the time and source of fertilizer but not by water management. With top dressing at primordial initiation, the fertilizer-N was more efficiently absorbed by the plant (74.3% for ammonium sulfate and 46.2% for urea). A similar trend was observed with other water management practices