Long-term Straw Retention And Nitrogen Fertilization Effects On Soil Physiochemical Properties,N₂O Emission And Yield Of Wheat-soybean Rotation System

Nitrogen loss and N₂O emissions caused by excessive fertilization are important sources of greenhouse gases.The effect of straw storage and fertilizer cultivation is significant,which is an important measure of greenhouse gas emission reduction in farmland.but how to combine with chemical fertilizer resources still needs to be further explored.As a planting system with the combination of use and cultivation,wheat-bean rotation system is of great value to popularize in Guanzhong Plain.The study of straw retention and nitrogen fertilizer application has important guiding value for greenhouse gas emission reduction in Guanzhong Plain.In this study,the wheat-bean rotation was selected as the research object to continue the long-term in-situ field experiment（2010）with split design.The main plots were the amount of straw retention to the field,including straw retention（S0）,half straw retention（S0.5）and straw retention（S）.The subplots were the level of nitrogen fertilizer application,including no nitrogen fertilizer（F0）,reduced nitrogen application（F0.8）and conventional nitrogen application（F）,which consists of 9 treatments.Through the positioning and monitoring of soil physiochemical properties,N₂O emission and yield indexes,the internal relationship of each index and its response to the treatment were clarified.The main results are as follows:（1）Long-term straw retention with nitrogen fertilizer effect on soil physiochemical propertiesStraw retention combined with reasonable nitrogen application can adjust soil temperature and increase soil mater storage,promote the content of soil carbon and nitrogen content.Among them,S improved significantly compared with S0.The content of total nitrogen（TN）、nitrate nitrogen（NO3--N）and ammonium nitrogen（NH4+-N）in F0.8 was significantly lower than that in F,and microbial biomass carbon（MBC）between F0.8 and F.However,the content of soil microbial biomass nitrogen（MBN）in F0.8 was significantly higher than that in F0 and F.（2）Long-term straw retention combined with nitrogen fertilizer effect on N₂O emission and crop yield in farmlandFertilization increased the N₂O emission rate,and accurs a peak after fertilization.N₂O cumulative emission in soybean season was higher than that in wheat season.Compared with F0,the N₂O emission of F0.8 increased by 56.1%-79.8%（wheat）and 85.2%-105.4%（soybean）.Straw retention to the field can promote N₂O emission,and S compared with S0 8.5%-22.1%（wheat）and 12.6%-30.9%（soybean）.S-F0.8 t significantly reduced N₂O emissions by 11.8%（wheat）and 7.7%（soybean）compared with S-F.Straw retention had very limited effect on crop yield increase,but straw retention combined with nitrogen fertilizer could significantly increase crop yield.S-F0.8 treatment significantly increased wheat yield by 7.1% and soybean yield by 9.5% compared with S0-F.Under F0.8,the nitrogen partial productivity and nitrogen agronomic efficiency of crops were significantly improved compared with conventional n application（F）,while the yield had no significant difference compared with F treatment.S-F0.8 had the best N partial productivity and N agronomic efficiency,which were 36.7 kg grain·kg N-1,9.3 kg grain·kg N-1（wheat）,15.4 kg grain·kg N-1,4.5 kg grain·kg N-1（soybean）.（3）Correlation between soil physiochemical properties and soil N₂O emission and crop yield The contents of NH4+-N and NO3--N were significantly positively correlated with soil N₂O emission.Which may be the main environmental factor affecting N₂O emission.At the same time,there was a positive correlation between soil N₂O emission and soil organic carbon content.There was a negative correlation between soil total nitrogen content and N₂O emission in wheat season,but on the contrary in soybean season.SOC had the strongest correlation with wheat yield,while TN had the strongest correlation with soybean yield.In summary,S-F0.8 not only ensured crop yield,but also reduced soil N₂O emissions,improved soil nitrogen residues,increased nitrogen use efficiency,and played a positive role in stable yield cultivation,nitrogen fixation and emission reduction in wheat-bean rotation cropping system in Guanzhong Plain.