Study On Rice Yield Differences And Nutrient Mechanism Between Rapeseed-rice And Wheat-rice Rotation Systems

The Yangtze River Basin is the main production area of winter rapeseed,and it is also an important base for the rapeseed-rice?RR?and wheat-rice?WR?rotation systems in China.Rapeseed oil is a traditional edible oil,and various functions of rapeseed has gradually developed in recent years in China.However,since 2011,area harvested and production of rapeseed continued to decline in China.Farmers'enthusiasm for rapeseed cultivation was greatly limited by the high cost and low efficiency.Therefore,further clarifying the dominant position of rapeseed in the rotation and putting it into the crop rotation system are of great significance to the sustainable development of the rapeseed industry and agriculture.In order to explore the differences of rice yield between the two rotation systems and analyze the mechanism,RR and WR rotation systems were studied.The study combined large-scale fertilization field experiments'data and literature data,and the database of yield,fertilization,nutrient uptake and nitrogen loss were established for RR and WR rotation systems.By synthetically data analysis,the difference of rice yield and its response to nitrogen?N?fertilizer of the two rotation systems were compared,also including the comprehensive evaluation of soil chemical fertility,and further exploring the nutrient budget difference.Otherwise,the study assisted the allelopathic experiment to expound the mechanism of rapeseed benefit to soil fertility.The main results are as follows:1.There was significant difference in rice yield between the two rotation systems.Especially in the N₀ treatment,the rice yield of RR?6469 kg/hm²?was 420 kg/hm²higher than the WR rotation system?6049 kg/hm²?.To achieve the 95%of highest yield,N application rate would be 168 kg N/hm² for the RR,which was significantly lower than that of the WR rotation system?180 kg N/hm²?.The economically optimal yield and nitrogen rate were similar with the above results.The RR rotation showed a better fertilizer-saving effect under the same rice yield level.Soil organic matter,total N and available N content of RR rotation were 14.2%,10.4%and 25.1%higher than WR rotation system,respectively.The soil comprehensive attribute score of RR?0.129?was significantly higher than WR rotation system?-0.128?.2.With no straw returning to the field,nutrient budget of the RR was 51.8 kg N/hm²,58.4 kg P₂O₅/hm² and-145.0 kg K₂O/hm²,and-0.4 kg N/hm².53.3 kg P₂O₅/hm²and-138.3 kg K₂O/hm² in the WR.Among of which,soil potassium was deficit,and N was surplus in RR but keep balance and/or slightly deficit in WR rotation system.With the straw returning,nutrient budget changed to 147.5 kg N/hm²,93.1 kg P₂O₅/hm² and229.0 kg K₂O/hm² for the RR,and 107.2 kg N/hm²,90.2 kg P₂O₅/hm² and 178.0 kg K₂O/hm² for the WR.Fallen leaves of rapeseed was an important source of nutrient during the rapeseed season.3.There was no significant difference in N loss between RR and WR rotation systems.Annual averaged N loss was 82.24-83.20 kg N/hm²,accounting for 21%of the annual N application rate.The N loss proportion was highest in NH₃ volatilization?12.0%?,then N leaching?3.8%-4.8%?and run off?4.0%-4.5%?,and the lowest through N₂O emission?0.9%?.The amount of N loss for rice season was about twice of the winter crop season.Otherwise,through literature analysis,quantitative equations for N₂O emission,NH₃ volatilization and nitrogen rate were established for the two rotation systems.Through optimal fertilization management,there were large greenhouse gas emission reduction potentials for the growing seasons of rice?2.3 Tg CO₂ eq?,rapeseed?0.69 Tg CO₂ eq?,and wheat?0.44 Tg CO₂ eq?in the Yangtze River basin.4.Two types of straw decomposing liquids had no significant effects on rice seed germination.The aboveground dry weight and plant height of rice treated with rape straw decomposition were significantly higher than those treated with wheat straw decomposition under 100 and 500 kg/mu straw returning amounts.Under the condition of distilled water decomposition,the aboveground dry weight of rice treated with rape straw was 10.7%-44.4%higher than that treated with wheat straw.Under the condition of nutrient solution decomposition,the aboveground dry weight of rice treated with rape straw was 2.2%-12.1%higher than that treated with wheat straw.The difference in nutrient between different straw decomposing liquids was an important factor affecting the growth of rice seedlings.At the same time,the presence of allelochemicals in the rapeseed straw decomposing liquid could better promote rice growth.In summary,the rice yield of the R-R rotation system was 420 kg/hm² higher than that of the W-R rotation.The higher soil chemical comprehensive fertility of R-R rotation was the main reason for the difference between the two rotation systems.Among them,the rapeseed season had more nitrogen surplus to supply rice in the later season.In addition to nutrient,the rapeseed planted in the previous season could also produce allelochemicals to promote the growth of rice.