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Late-season nitrogen applications improve grain yield and fertilizer-use efficiency of dry direct-seeded rice in the tropics

Liu, Hongyan, Won, Phyo L.P., Banayo, Niño P.M., Nie, Lixiao, Peng, Shaobing, Kato, Yoichiro
Field crops research 2019 v.233 pp. 114-120
Oryza sativa, canopy, cultivars, direct seeding, dry season, fertilizer application, field experimentation, filling period, grain yield, harvest index, heading, leaves, nitrogen, nitrogen fertilizers, panicles, research institutions, rice, temperature, tropics, vegetative growth, wet season, Philippines
Efficient nitrogen (N) management plays an important role in rice cultivation. Previous studies in the tropics mainly focused on split-N applications before panicle initiation in transplanted rice. In this study, we examined the effects of top-dressing at panicle initiation and flowering of dry direct-seeded rice on yield and fertilizer-use efficiency in field experiments at the International Rice Research Institute, the Philippines, in the dry and wet seasons. Two high-yielding indica cultivars (Rc222 and Rc282) were drill-seeded under four split-N application regimes and a control with no supplemental N. The timing of the split-N applications significantly affected grain yield, even though the total N input was unchanged. The late-season N application at heading increased yield by 6% (0.49 t ha−1) in the dry season and 7% (0.49 t ha−1) in the wet season. The N recovery efficiency also increased with an increasing proportion of N applied at later growth stages. The yield advantage of the late-season N application over the early-season N application (seeding to panicle initiation) may be attributable to delayed senescence (maintenance of more and greener leaves toward maturity), higher canopy photoassimilation, greater grain-filling, and a higher harvest index. Our results underline the importance of late-season N application in dry direct-seeded rice under favorable lowland conditions in the tropics. The optimal split-N regimes during the vegetative stage may depend on the season or temperature regime, so this subject requires additional investigation.