| Excessive use of nitrogen fertilizer in rice production in China not only reduces nitrogen use efficiency and increases costs,but also causes significant pollution to agriculture and the ecological environment.Therefore,reducing nitrogen fertilization has become an inevitable choice for modern rice cultivation.Reducing nitrogen use while maintaining high yields is a complex problem that requires selecting varieties with high nitrogen absorption efficiency and determining reasonable and appropriate cultivation management measures.At the same time,serious rural labor outflow in China has made it important to pursue high-yield and highquality machine-transplanted rice in order to ensure food security and improve full-process mechanization of rice production.However,there is still a lack of systematic research on how nitrogen levels and transplanting methods interact with planting density to affect rice yield and quality.In this study,new cultivars developed by Yangzhou University,including Wumijin and Yangnongjing 1030,as well as Huaidao 5 and Nanjing 46,which have relatively good yield and rice quality,were used as experimental materials for field planting.By conducting combination experiments of nitrogen application levels and transplanting methods and densities,the study analyzed the effects of nitrogen fertilizer levels and cultivation management measures on rice yield and its compositional factors,material production and distribution,and rice quality.Additionally,the study compared the differences in rice quality under different saltwater ratios.The research results have certain guiding significance for accurately evaluating nitrogen fertilizer effects,reasonable use of high-yield genes,and balancing and optimizing the relationship between reducing nitrogen fertilizer input and ensuring stable yield and high quality rice production.The main results are as follows:1.Rice grain yieldUnder various nitrogen application levels and transplanting methods,the yield of Yangwumi was higher than that of the other three varieties.Although Yangwumi is not excellent in terms of seed setting rate and thousand grain weight,it has the highest number of panicles and larger total spikelet yield at various nitrogen application levels,leading to the highest yield.Under N16 treatment,the number of panicles per unit area and grains per panicle of rice increased,but it decreased the seed setting rate and thousand grain weight of nce.Under the same variety and nitrogen fertilizer level,the number of panicles per unit area of machine transplanted seedlings is significantly higher than that of hand transplanted seedlings,but the number of grains per panicle,seed setting rate,and thousand grain weight are lower than those of hand transplanted seedlings,ultimately resulting in a decrease in yield.Under hand transplanting treatment,the yield of Huaidao 5 reached its peak under N12 treatment,while the yield of the other three varieties was the highest under N16 treatment;However,during machine transplanting treatment,all four varieties showed the highest yield under N12 treatment,and the yield rate under N16 treatment was lower than that under N12 treatment.Under the same variety and nitrogen fertilizer level,the yield of machine transplanting is significantly lower than that of hand transplanting.2.Dry matter production and distributionUnder N16 treatment,the overall dry matter content of rice at heading stage increased,and the peak dry matter content at heading stage affected by nitrogen varied among different varieties.Huaidao 5 reached its peak under N12 treatment,and continued to increase nitrogen,resulting in a decrease in dry matter production.Due to the influence of transplanting methods,the number of panicles per unit area of machine transplanting treatment is higher,and the dry matter production during the heading period of rice increases.Under the same nitrogen level treatment,the overall dry matter production is higher than that of hand transplanting treatment.Under N16 treatment,the harvest index of rice increased.The harvest index of machine transplanting was significantly lower than that of hand transplanting.There is a significant interaction effect between genotype,transplanting method,nitrogen fertilizer,and transplanting method on dry matter production and harvest index.In terms of dry matter weight ratio,the stem sheath dry weight ratio and ear dry weight ratio of the four varieties at heading stage were negatively correlated with nitrogen application rate,while the leaf dry weight ratio was significantly positively correlated with nitrogen application rate.Under N16 treatment,the increase in leaf dry weight during heading period under hand transplanting was significantly higher than that under machine transplanting.The dry weight of panicles during heading period under hand transplanting treatment was significantly greater than that under machine transplanting treatment.The trend of dry weight ratio change during the mature period is not entirely the same.Under two transplanting methods,the proportion of dry weight per panicle at maturity of the four varieties was positively correlated with nitrogen application rate;There is a significant negative correlation between the dry weight ratio of stem and sheath during the mature stage and nitrogen application rate.Under the same nitrogen level treatment,the proportion of dry weight per panicle at maturity of the four varieties under hand transplanting treatment was generally higher than that under machine transplanting treatment.3.Rice grain qualityThe trend of the impact of different rice varieties’ processing quality on different nitrogen application rates is not the same.The appropriate nitrogen application rate has a promoting effect on the processing quality of Huaidao 5 and Yangwumi,while the processing quality of Nanjing 46 and Yangnongjing 1030 decreases with the increase of nitrogen application rate.Under N16 treatment,the appearance quality of rice significantly decreased,and the chalkiness and chalkiness percentage of rice significantly increased.Under hand transplanting treatment,the chalkiness index of all four varieties reached its peak under N16 treatment.However,under machine transplanting treatment,the chalkiness index of Nanjing 46 reached its peak under N12 treatment,while the chalkiness index of the other three varieties reached its peak under N8 treatment.Among the four varieties,Yangnongjing 1030 has the best appearance quality,while Nanjing 46 has the worst appearance quality.The appearance quality of rice is significantly affected by density,and the chalkiness and chalkiness percentage of rice under high-density treatment are significantly higher than those under lowdensity treatment.The effect of nitrogen application rate on amylose content is not significant.With the increase of nitrogen application rate,the protein content of the four varieties of rice has been improved to varying degrees.The application of nitrogen fertilizer and machine transplanting can both reduce the taste value of rice.Among the four varieties,Nanjing 46 has the highest taste value,and the decrease in taste value is most significant after nitrogen application.Reducing nitrogen appropriately can improve the appearance quality,processing quality,and cooking taste quality of rice,while the nutritional quality is the opposite.The impact trend of different transplanting methods on rice quality is relatively consistent,and the rice quality under hand transplanting is better than that under machine transplanting.The processing quality of rice increases first and then decreases with the increase of salt water proportion,and the processing quality of grains with high filling degree is poor.The appearance quality of grains with high plumpness is improved,and the chalkiness and chalkiness percentage are significantly reduced.The nutritional quality of grains with high plumpness decreases,protein content and amylose content decrease,and taste value improves. |
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