Characteristics Of Nutrient Requirements And Reasonable Management Of Nitrogen Fertilizer In Rice-ratoon Rice System

By improving the multiple cropping index of cultivated land to protect the sown area of rice is an important measure to ensure the high and stable rice production,to ensure China's food security.In recent years,due to the reduction of agricultural labor force,high labor costs,low net income,double cropping rice sown area decreased,which resulted in a sharp reduction of rice sown area.The ratoon rice has the characteristics of short growth period,low input of the seed and labor,high economic efficiency.Planting ratoon rice has become another important measure to increase the cropping index and the rice yield per unit area.Studying the nutrient uptake,utilization and rational fertilization of rice-ratoon rice system is significant to obtain high yield and high efficiency of rice in China.In this study,two years field trials were conducted to clarify the rule of dry matter accumulation,nutrient uptake and transport of the rice-ratoon rice system.The effects of different time of nitrogen application and amount of bud fertilizer on the yield of ratoon rice were discussed.The effect of nitrogen application on the yield and nitrogen use efficiency of rice-ratoon rice system was discussed in order to provide theoretical reference of efficiency nitrogen management.The main results are summarized below.1.The total dry matter accumulation in the main rice was the growth trend of "slow-fast-slow" in the whole growth period.The rapid accumulation period of the total dry matter was between jointing stage and filling stage.Dry matter accumulation in ratoon rice appeared S-type curve,and its rapid growth occurred at harvest of main rice to heading stage.The dry matter accumulation of stem and leaf continued to grow in the filling stage.The dry matter weight of stubble was from the photosynthesis of stem and leaf in the lower part of main rice,which decreased after harvest of main rice.And the dry matter accumulation of stem and leaf in the ratoon rice were transferred from stubble.2.The total accumulation of nitrogen(N)in the main rice and ratoon rice showed an increasing trend.The growth rate of the main was relatively stable,and the ratoon rice showed “fast-slow” trend.The total accumulation of phosphorus(P)in the main rice and the ratoon rice was increased first and decreased.Potassium(K)accumulation in the main rice reached maximum at filling stage,decreased after heading stage in the ratoon rice.The nutrient accumulation of stubble is the main source of N,P and K of ratoon rice in earlier growing stage.After harvest of the main rice,N,P and K nutrient accumulation of stubble decreased 60.0%,79.0% and 84.4%,respectively.3.The combined application of bud fertilizer and tiller fertilizer obtaining a better yield of ratoon rice than single fertilization,the yield response of ratoon rice to bud fertilizer could be described by the model of linear plus plateau.Under the experimental conditions,the appropriate amount of bud fertilizer is 60 kg N /hm2.And then use 60 kg N/hm2 tiller fertilizer increased by 13.0%-17.6% of the number of ratooning buds in the germination stage,and decreased death rate in the late period of ratooning buds.The effects of single application of bud fertilizer was decreased effective panicle number of ratoon rice due to lack of N.The effects of single application of tiller fertilizer was increased the mortality of ratooning buds and decreased effective panicle number due to shorten growth period.On the other hand,the application of high bud fertilizer was not significant increased the yield of ratoon rice,but decreased by 20.9% and 28.1% of agronomic efficiency of applied N and partial factor productivity from applied N respectively.4.The effect of optimal N application on the yield and nitrogen use efficiency of rice-ratoon rice system was the best.The effect of increasing N fertilizer or changing nitrogen applicationon on the yield of rice-ratoon rice system was not significant compared with the optimal treatment,but significantly reducing N use efficiency.Under this experimental condition,the effect of fertilization on the yield of ratoon rice was better than that of the main rice by increasing panicles and spikelets per panicle.Appling high N or increased panicle fertilizer in the main rice increased the accumulation of dry matter and nutrients by about 10%-20%,but did not significantly of sink capacity,even reduced by 15.3%-30.5% of nitrogen use efficiency.The effect of later N topdressing on the yield and N use efficiency was similar of the optimal treatment.The increase of the amount of bud fertilizer was not conducive to the improvement of the yield and nitrogen use efficiency.Increasing panicle fertilizer increased the spike rate of the ratoon rice,but decreased the seed setting rate.