Characteristics of yield determination and N uptake in direct-seeded rice as affected by planting methods

To achieve high yields and stable production in direct-seeded rice, there is a need to stabilize crop establishment and to understand yield-determining processes, in rice growth under various seeding methods. Three direct seeding methods, surface broadcast, anaerobic broadcast, and anaerobic drill and transplanting were compared for crop establishment, growth characteristics, and N uptake pattern at an IRRI [Philippines] lowland field. Three lowland genotypes were used: IR41996-50-2-1-3 and IR52341-60-1-2-1, tolerant to anaerobic seeding, and PSBRc 4 as control. Grain yield was first related to spikelet number per unit area across crop establishment methods. The interaction of plant types and crop establishment methods, direct seeding and transplanting to grain yield indicated the importance of selecting suitable genotypes for each establishment method. Higher plant population in broadcast seeding led to higher tiller and panicle number per unit area compared with transplanting, but spikelet number per panicle decreased. During the initial growth stage, dry matter and N accumulation in broadcast-seeded plants were much faster than in transplanted plants, but they slowed down after the late vegetative stage. This resulted in unstable yield due to a decrease in spikelet number, especially in high tiller-type genotypes, in broadcast seeding. Nitrogen content in the shoot was much lower in the early stage in direct seeding than in transplanting. The difference remained until maturity. Root density increased in direct seeding compared with transplanting in the surface layer, but not in the subsoil. Lower N uptake might be partly associated with shallower roots in direct-seeded rice. Anaerobic drill seeding showed intermediate growth and N uptake might be partly associated with shallower roots in direct-seeded rice. Anaerobic drill seeding showed intermediate growth and N uptake for both transplanting and broadcast seeding. Repeated field trials in IRRI and PhilRice confirmed that anaerobic drill seeding can reduce yield fluctuation compared with broadcast seeding. Anaerobic drill seeding using anaerobic-tolerant genotypes could effectively stabilize the yield in direct seeding