NITROGEN USE EFFICIENCY OF IRRIGATED TROPICAL RICE ESTABLISHED BY BROADCAST WET-SEEDING AND TRANSPLANTING

Broadcast wet-seeding is gradually replacing transplanting in irrigate d rice systems of Southeast Asia. Previous studies reported higher fer tilizer-N use efficiency for broadcast-seeded than transplanted rice d espite similar grain yields in treatments that received N fertilizer. To re-examine this issue, we compared crop performance and the recover y efficiency (epsilon(r) Delta N uptake per unit N applied), agronomic efficiency (epsilon(a), Delta grain yield per unit N applied), and pa rtial factor productivity from applied N (PFP, grain yield per unit N applied) in broadcast-seeded and transplanted rice across a wide range of N fertilizer rates at research stations and in farmers' fields. Ri ce crop established by broadcasting had more rapid leaf area developme nt, dry matter accumulation, and N uptake than transplanting during ve getative growth stages, but slower growth rates and N uptake after pan icle initiation, particularly during the grain filling period. Without applied N, grain yield and N accumulation at maturity were significan tly lower in broadcast-seeded than transplanted rice, whereas yields a nd N uptake were comparable for both planting methods with equivalent rates of applied N. Although both epsilon(r) and epsilon(a) were highe r for broadcast-seeded than transplanted rice, this advantage was an a rtifact of lower yields and reduced N uptake by broadcasting without a pplied N rather than improved performance with applied N. In contrast, PFP values were similar for broadcast-seeded and transplanted rice at comparable fertilizer-N rates and in the absence of lodging. We concl ude that the PFP from applied N provides a more relevant measure of N use efficiency of different crop establishment methods, and that the s ystem-level N use efficiency of broadcast-seeded rice was not greater than that of transplanted rice.