Yield of no-tillage direct-seeded lowland rice as influenced by different sources and application methods of fertilizer nitrogen

Due to high the labor cost, direct seeding is being gradually applied for c rop establishment throughout Asia. Recently, the development of the so-call ed, "controlled release fertilizers" (CRFs) which requires only "one shot d ose" of N, has enabled to reduce the cost of labor for the application of t opdressed N. Thus, in order to limit pollution and cost, no-tillage direct- seeded lowland rice cultivation accompanied by the use of CRF is being reco mmended. To evaluate the effects of CRFs on the growth and yield of no-till age direct-seeded rice, a field experiment was carried out in the north-eas tern region of Japan in 1993 and 1994. Five N treatments were used: (1) amm onium sulfate (AS) band placement application with seeds at the time of see ding (AS1); (2) AS broadcast application after irrigation (AS2); (3) CRF (L P100) co-situs application at the time of seeding (L1); (4) CRF (LPS100) co -situs application at the time of seeding (L2); and (5) minus N (MN). The r ate of basal N was 60 kg N ha(-1) Topdressed N in the AS1 and AS2 treatment s was applied at 25 d before heading at the rate of 20 kg N ha(-1). The hig hest yield was obtained in the L1 treatment in both years. The number of gr ains per unit area was affected by the amount of N in the plants at heading . The percentage of filled grains in the L2 treatment was the lowest by abo ut 15 to 20% among the treatments. The recovery percentages of basal N on J uly 20 were about 20 to 30% in the AS1, AS2, and L1 treatments, and only ab out 14% in the L2 treatment. About 75 to 80% of basal N was absorbed by the plants at harvest in the L1 and L2 treatments. On the other hand, the plan ts had absorbed only about 25 to 30% of the applied basal N in the AS1 and AS2 treatments at harvest. There was no difference in the N-recovery percen tage (based on the amount of released N) between the L1 and L2 treatments. Nitrogen-use efficiency was not significantly different among the treatment s. However, higher N-use efficiency was obtained in this experiment than in early studies in the tropics. The agronomic efficiency of CRFs was higher than that of ammonium sulfate.