Effects of nitrogen reduction on grain yield and quality of mechanical transplanting hybrid indica rice

【Objective】To study the effect of nitrogen reduction on grain yield and quality of mechanical transplanting hybrid indica rice and provide a theoretical basis for reasonable nitrogen reduction in mechanical transplanting hybrid indica rice cultivation.【Method】Based on the nitrogen application rate（180 kg/ha，CK）for high-yield cultivation of the variety，the effect of nitrogen reduction［30 kg/ha of nitrogen reduction，（N_-30）；60 kg/ha of nitrogen reduction，（N_-60）and no nitrogen application，（N₀）］on grain yield，processing quality，appearance quality，nutritional quality，cooking and eating quality of mechanical transplanting hybrid indica rice were investigated in Guiyang and Meitan with rice varieties Yixiangyou 2115 and F you 498 as materials.【Result】The grain yield and quality of mechanical transplanting hybrid indica rice were basically the same changes after nitrogen reduction in Guiyang and Meitan. With the increase in the degree of nitrogen reduction，the total number of spikelets and grain yield of mechanical transplanting hybrid indica rice gradually decreased，processing quality（brown rice rate，milled rice rate，and head milled rice rate）of rice first increased and then decreased，and appearance quality（chalkiness percentage and chalkiness degree）and protein content of rice gradually decreased，while the cooking and eating quality of rice（gel consistency and amylose content）gradually increased，and comprehensive of rice increased. Compared with CK，the total number of spikelets and grain yield of hybrid indica rice in nitrogen reduction decreased by 4.43%-35.08% and 1.76%-38.77%，respectively；the chalkiness percentage，chalkiness degree and protein content of rice decreased by 2.08%-29.58%，3.57%-45.33% and 3.10%-21.37%，respectively；the gel consistency，amylose content，comprehensive of rice increased by 3.89%-49.28%，0.52%-13.24% and 0.25%-5.67%，respectively；the change trend of rice processing quality at the two ecological sites in the same nitrogen reduction treatment was slightly different，but the overall difference was small. Correlation analysis showed that there was extremely significant positive correlation between grain yield and total number of spikelets（P<0.01，the same below）. The grain yield and the total number of spikelets were significantly（P<0.05，the same below）or extremely significantly negatively correlated with the most of the cooking and eating quality of rice（gel consistency，alkali spreading value and comprehensive），and were significantly or extremely significantly positively correlated with processing quality（brown rice rate and milled rice rate），appearance quality（chalkiness percentage and chalkiness degree）and protein content of rice.【Conclusion】An appropriate amount of nitrogen reduction（N_-30）can improve processing quality，appearance quality and cooking and eating quality of mechanical transplanting hybrid indica rice，while the grain yield can still be maintained above 9.80 t/ha，synergistically to achieve stable yield and high quality of mechanical transplanting hybrid indica rice. However，excessive nitrogen reduction（N_-60 and N₀）can improve the appearance quality and cooking and eating quality of rice，but the processing quality of rice tends to deteriorate and grain yield of rice is significantly reduced，which is difficult to achieve high yield of mechanical transplanting hybrid indica rice.