Rice (Oryza sativa L.) plants grown in southwestern Japan are subjected to large variations in air temperature and solar radiation during the rainy season which can affect their growth. Therefore, in this study, a novel nitrogen (N) application method for topdressing was proposed to increase grain yield under different weather conditions. Field experiments were conducted to determine the grain yield response to the soil and plant analyzer development (SPAD) readings and normalized difference vegetation index (NDVI) during the early reproductive stage in 2018 and 2019. As the rainy season ended in early July in 2018 but continued until late July in 2019, the daily mean solar radiation during the vegetative and early reproductive stages was 26% lower in 2019 than in 2018. Grain yield was 10% lower in 2019 than in 2018, mainly due to the lower number of spikelets. During the early reproductive stage, the SPAD readings and NDVI were higher in 2019 than in 2018, suggesting that the biomass and N concentration in 2019 were lower and higher than those in 2018, respectively. Statistical modeling examination of grain yield response to growth‐related factors revealed that the N application rate during the reproductive stage and SPAD readings were significant predictors in 2018, whereas the N application rate and NDVI were significant predictors in 2019. Our findings suggest that SPAD readings and NDVI are key factors for determining N application rate during the reproductive stage under higher and lower solar radiation conditions during the vegetative and reproductive stages, respectively.

中文翻译：

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一种提高日本西南部水稻产量的天气适应追肥方法

水稻（水稻在日本西南部生长的植物（L.）在雨季期间会遭受气温和太阳辐射的极大变化，这可能会影响其生长。因此，在这项研究中，提出了一种新颖的追施氮肥的方法，以增加不同天气条件下的谷物产量。进行了田间试验以确定2018年和2019年早期生殖阶段对土壤和植物分析仪发育（SPAD）读数和归一化植被指数（NDVI）的谷物产量响应。由于雨季于2018年7月初结束，但持续到2019年7月下旬，营养和生殖早期的日平均太阳辐射在2019年比2018年降低了26％。2019年的谷物产量比2018年降低了10％，这主要是由于小穗数量减少所致。在生殖早期，2019年的SPAD读数和NDVI高于2018年，这表明2019年的生物量和氮浓度分别低于和高于2018年。谷物产量对生长相关因子响应的统计模型检验显示，生殖阶段的氮肥施用量和SPAD读数是2018年的重要预测指标，而氮肥施用量和NDVI是2019年的重要预测指标。我们的发现表明SPAD读数NDVI和NDVI分别是确定营养阶段和生殖阶段较高和较低太阳辐射条件下生殖阶段氮肥施用量的关键因素。表明2019年的生物量和氮浓度分别低于和高于2018年。谷物产量对生长相关因子响应的统计模型检验显示，生殖阶段的氮肥施用量和SPAD读数是2018年的重要预测指标，而氮肥施用量和NDVI是2019年的重要预测指标。我们的发现表明SPAD读数NDVI和NDVI分别是确定营养阶段和生殖阶段较高和较低太阳辐射条件下生殖阶段氮肥施用量的关键因素。表明2019年的生物量和氮浓度分别低于和高于2018年。谷物产量对生长相关因子响应的统计模型检验显示，生殖阶段的氮肥施用量和SPAD读数是2018年的重要预测指标，而氮肥施用量和NDVI是2019年的重要预测指标。我们的发现表明SPAD读数NDVI和NDVI分别是确定营养阶段和生殖阶段较高和较低太阳辐射条件下生殖阶段氮肥施用量的关键因素。