Effects Of Crop Straw Returning And Nitrogen Fertilizer Management On Rice Yield And Nitrogen Use Efficiency

Rice is the largest grain crop in China.Its cultivated area accounts for about 27%of the total cultivated land and its output accounts for about 40%of the total grain production in China.At present,there are many problems in rice production,such as excessive fertilization,low nitrogen utilization rate,and difficult to effectively return the previous crop straw to the field.Previous studies on the effects of straw returning and nitrogen fertilizer operation on rice yield and nitrogen use efficiency mostly focused on a single straw type,but there were relatively few studies on the effects of different straw returning nitrogen application ratio on rice yield and nitrogen use efficiency.In this study,under the total nitrogen application rate of 270kg hm-2,Nanjaponica 9108 and Huaidao 5 were used as materials.Under the condition of wheat/rape straw returning to the field,the two nitrogen application ratios were set to study their effects on rice yield,nitrogen use efficiency and some soil nutrients.Three nitrogen management modes of inorganic nitrogen fertilizer,inorganic nitrogen fertilizer combined with organic fertilizer,and slow-release fertilizer combined with organic fertilizer were set based on the ratio of increased base fertilizer application with high yield(base fertilizer,tillering fertilizer,ear fertilizer=7:1:2)to study the effects on rice yield,nitrogen use efficiency and some soil nutrients.In order to screen out the suitable straw returning and nitrogen fertilizer management mode under the condition of wheat/rape straw returning,and to provide theoretical and practical basis for high yield cultivation of rice.The main research conclusions are as follows:1.Compared with conventional nitrogen application(base fertilizer,tillering fertilizer,ear fertilizer=5:1:4),increasing the ratio of base fertilizer(base fertilizer,tillering fertilizer,ear fertilizer=7:1:2)reduced the percentage of tiller heading,leaf area index at heading stage and dry matter accumulation at heading to maturity stage,which significantly reduced rice yield.Under the normal nitrogen application ratio,the grain number and grain weight per panicle were increased to some extent,and the yield was slightly increased.Under wheat(rape)straw returning,combined with base fertilizer:tillering fertilizer:ear fertilizer=7:1:2 nitrogen fertilizer management mode could achieve high yield of rice,which increased by 10.34%to 11.70%(13.79%to 14.89%)compared with conventional nitrogen application under straw not returning.Under the same nitrogen application ratio,compared with wheat straw returning to field,rape straw returning to field resulted in higher panicle number and grain number per panicle,and slightly increased rice yield,but grain weight and seed setting rate were lower than that of wheat straw,so rice yield was not significant among straw types.2.Under the same nitrogen application ratio,straw returning reduced the nitrogen accumulation before jointing,but increased the nitrogen accumulation from jointing stage to heading stage and from heading stage to maturity stage,and improved various indexes of nitrogen use efficiency.Compared with conventional nitrogen application,increasing the proportion of base fertilizer further increased nitrogen accumulation before jointing and from jointing to heading stage,but decreased nitrogen accumulation from heading to maturity stage.In terms of soil nutrients,straw returning increased the contents of soil organic matter,total nitrogen,ammonium nitrogen and nitrate nitrogen at maturity stage under the same nitrogen application ratio.At the same time,soil nutrient indexes of rape straw were higher than those of wheat straw.3.Under the condition of wheat(rape)straw returning,fertilizer type had significant effects on rice yield and dry matter accumulation.Compared with urea alone,urea combined with organic fertilizer and slow-release fertilizer combined with organic fertilizer significantly increased panicle number per unit area,1000-grain weight and seed setting rate.Urea combined with organic fertilizer increased yield by 2.13%-5.49%(4.12%-6.52%),slow release fertilizer combined with organic fertilizer increased yield by 4.17%-6.59%(6.52%-9.78%),and there was no significant difference in yield between the two organic fertilizer treatments.Urea combined with organic fertilizer decreased dry matter accumulation at tillering stage,but increased dry matter accumulation at jointing stage to maturity stage.However,slow release fertilizer combined with organic fertilizer increased dry matter accumulation at different growth stages of rice.Under the same fertilizer type,the rice yield and dry matter accumulation of all periods were better than those of wheat straw.4.Under the condition of wheat(rape)straw returning,urea combined with organic fertilizer reduced the nitrogen accumulation of rice before jointing,but significantly increased the nitrogen accumulation from jointing to heading and heading to maturity.The nitrogen accumulation of slow-release fertilizer combined with organic fertilizer was higher than that of urea alone.The above two treatments improved the indices of nitrogen use efficiency of rice.For soil nutrients,compared with urea alone,urea combined with organic fertilizer could increase the content of soil organic matter and total nitrogen,and increase the content of soil mineral nitrogen at maturity stage.Meanwhile,slow release fertilizer combined with organic fertilizer is beneficial to further improve the above indexes.