Nitrogen and density treatment to improve resource utilization and yield in late sowing <italic>japonica</italic> rice

Abstract

<p id="C3">Recently, the phenomenon of late sowing and late transplanting in rice is becoming more and more common in central Jiangsu, a rice and wheat double cropping system area, which is caused by climate change and the expanding of comprehensive rice-and-shrimp planting model. It will lead to the mismatch of rice growth period with light and temperature resources, restricting the stable high yield of rice. This study was conducted under the condition of late sowing and late transplanting (sowing date was June 12th, transplanting date was June 30th) and the seedling was transplanted by machine. Four nitrogen application rates (N₀: 0 kg hm^-2; N₂₄₀: 240 kg hm^-2; N₃₀₀: 300 kg hm^-2; N₃₆₀: 360 kg hm^-2) and three density treatments (D₃: 3 seedlings per hole; D₄: 4 seedlings per hole; D₅: 5 seedlings per hole) were arranged, and the suitable sowing period (May 29), conventional nitrogen application rate, and the seedling number per hole (N₃₀₀D₄) were taken as the controls. Our goal is to explore the effects of nitrogen fertilizer and seedling number per hole on the growth and yield formation in late-sown <italic>japonica</italic> rice, and to provide theoretical basis for improving yield potential and resource use efficiency in late sowing and late transplanting <italic>japonica</italic> rice in central Jiangsu province. The results showed that compared with CK, the yield of each treatment decreased, mainly because of the significantly reduced spikelet number under the late sowing and late transplanting condition. The highest spikelet numbers were 11.94% and 8.12% lower than those of CK in the two years. In addition, the utilization rate of temperature and light resources, nitrogen uptake, and nitrogen utilization rate decreased under late sowing and late transplanting treatment, leading to a decrease in dry matter accumulation and yield. The yield increased with the increase of nitrogen application rate and seedling number per hole under the late sowing and late transplanting condition, while there was no consistent with the trend under N₃₆₀D₅ treatment. We assumed that it was mainly due to the increased spikelet number, larger leaf area index at heading stage, the larger proportion of efficient leaf, and the extended growth period. In summary, the utilization of temperature and light resources and the dry matter accumulation at maturity stage was improved, and the decline in yield was alleviated. Nitrogen use efficiency increased first and then decreased with the increase of nitrogen rate, and N₃₀₀D₅ treatment reached the maximum. In general, under the late sowing and late transplanting condition, in order to alleviate the yield loss and reduce nitrogen fertilizer waste, we should increase the seedling number per hole and then increase the amount of nitrogen fertilizer.