Late nitrogen application enhances spikelet number in indica hybrid rice (Oryza sativa L.)

ABSTRACT To increase rice yield potential, field experiments were conducted in farmers’ paddies in 2011 and 2012 to evaluate the effects of different nitrogen applications on the yield and panicle components of three typical indica hybrid rice varieties in Sichuan Province. The number of grains per panicle resulting from late nitrogen application (LA) was 12 % greater than that obtained from traditional nitrogen application (TA); this increase was the main source of improvements in yield. The number of surviving and differentiated spikelets (NSS and NDiS) resulting from LA was significantly higher than that measured under TA, especially for the Fyou498 cultivar, where the NSS and NDiS increased by 15 % and 14 %, respectively. Compared with TA, the number of degenerated secondary branches and the percentage of degenerated secondary branches (NDeSB and PDeSB) were significantly reduced by 9 % and 11 %, respectively, by LA. This is the first study to demonstrate that an increase in NSS and a decrease in NDeSB lead to yield-improving effects attributable to LA. The grain yields of different varieties ranged from 9225.6 to 9408.7 kg ha−1, the PDeSB was as high as 31 %, and the number of surviving secondary branches (NSSB) was significantly and positively correlated with NSS. These data indicate that the yield of indica hybrid rice has considerable potential for being improved, and increasing NSSB is key to increasing NSS and improving the grain yield. These improvements should be pursued so as to increase the yield of hybrid rice to ensure both food security and sustainable agricultural development.

摘要 为提升水稻的产量潜力，本研究于2011年与2012年在四川省农户稻田开展田间试验，评估不同施氮方案对3个典型籼型杂交水稻品种的产量及穗部性状的影响。晚施氮肥（Late Nitrogen Application, LA）处理下的每穗粒数较传统施氮肥（Traditional Nitrogen Application, TA）处理高出12%，该增量是产量提升的主要来源。晚施氮肥处理下的存活与分化小穗数（Number of Surviving Spikelets, NSS；Number of Differentiated Spikelets, NDiS）显著高于传统施氮处理，尤以Fyou498品种最为突出，其NSS与NDiS分别提升15%与14%。相较于传统施氮处理，晚施氮肥处理可使退化二次枝梗数（Number of Degenerated Secondary Branches, NDeSB）与退化二次枝梗占比（Percentage of Degenerated Secondary Branches, PDeSB）分别显著降低9%与11%。本研究首次证实，晚施氮肥可通过提升存活小穗数、降低退化二次枝梗数实现增产效应。供试品种的稻谷产量区间为9225.6至9408.7千克·公顷⁻¹，退化二次枝梗占比最高可达31%，且存活二次枝梗数（Number of Surviving Secondary Branches, NSSB）与存活小穗数呈显著正相关。上述数据表明，籼型杂交水稻的产量具备可观的提升潜力，而提升存活二次枝梗数是增加存活小穗数、进而提升稻谷产量的关键。通过推进此类改良措施，可进一步提升杂交水稻产量，为保障粮食安全与农业可持续发展提供支撑。