Study On Agronomic And Environmental Effects Of Combined Application Organic And Chemical Fertilizers Under Winter Wheat And Summer Maize Cropping System

Winter wheat and summer maize,double cropping system,is the main cropping system in north China.A large number of studies have shown that the combined application of organic manure and chemical fertilizers can improve soil fertility and increase crop yield,but their effects on emissions of N₂O and other nitrogen（N）gases have inconsistent results.Moreover,the reasonable ratio between organic manure and chemical fertilizers in their combination also needs to be further studied.Based on three-year field experiment and modelling approach,the present study is to investigate the comprehensive effects of combined application of organic manure and chemical fertilizers on wheat and maize yields,N use efficiency,N gas emissions and N balance under winter wheat and summer maize rotation system on Lou soil in Guanzhong Plain of Shaanxi Province.There are 7 treatments involved in field experiment,i.e.no fertilization input as control（CK）,100%NPK supplied by chemical fertilizers（NPK）,25%,50%,75%and 100%of the N substituted by manure（recorded as 25%M,50%M,75%M and 100%M,respectively）,and wheat and maize straw return plus NPK（SNPK）.The manure amendment treatments received the same N input as NPK on an annual basis,345 kg N ha^-1yr^-1.The main results and conclusions obtained were as follows:（1）The 3 years field study showed that substituting 75%of chemical N by organic manure could optimize yield components and effectively increase crop yields compared with NPK treatment,while other proportion manure substitution treatments had equal crop yields to that of NPK treatment.Compared with NPK treatment,straw returning also significantly increased crop yield and optimized yield components,especially in the wheat season.Long-term simulation showed that different fertilization treatments were similar in wheat yield,and the variation was not significant different among different years.However,different fertilization treatments had a greater effect on maize yield and showed different performance.For example,compared with NPK treatment,25%M treatment had no effect on maize yield for all years,while 50%M,75%M and 100%M treatments produced lower yield than NPK treatment in the beginning of 6,10 and 15 years,respectively,and thereafter yield was similar among treatments.The effect of straw returning had no significant effect on crop yield relative to NPK treatment on tested years.（2）The results of field experiment also showed that N use efficiency presented a trend of increase first and then decrease with increasing proportion of manure N application,among which 75%M treatment was the highest.The yield increase on SNPK treatment was relatively low,resulting in a lower N use efficiency than NPK treatment.In general,the contents of nitrate N in 0-200 cm soil layer treated by NPK and SNPK were higher than that by manure amendment.The content of ammonium N in 0-200 cm soil layer were low,and there were no differences among different fertilization treatments.With the increasing of substitute ratio by manure N,the mineral N left in soil gradually decreased,while N balance showed an increasing trend,indicating that most of the soil N existed in the form of organic N in the manure amendment treatments.The mineral N left in soil and N balance under straw returning treatment were higher,so the amount of N input should be reduced when long-term straw returning would be performed.（3）Field monitoring results of gas emissions showed that fertilization treatments increased N₂O emissions in both wheat and maize seasons,especially in NPK and SNPK treatments,which were significantly higher than in manure amendment treatments.Also,N₂O emissions were the lowest under 75%M and 100%M treatments and showed no significant difference compared with CK treatment.In terms of N₂O emission intensity,75%M treatment can both ensure crop yield and reduce N₂O emission.In addition,the duration of ammonia（NH₃）volatilization peak in wheat season was longer than that in maize season,and the peak was also higher in wheat season than in maize season.Compared with NPK treatment,50%M,75%M and 100%M treatments can significantly reduce the annual NH₃ volatilization under wheat and maize rotation system,while SNPK treatment increased NH₃ volatilization.Long-term simulation of DNDC model on emissions of N gases（N₂O,NO,N₂ and NH₃）showed that fertilization can significantly increase N gas emissions,the effectiveness of treatments was in order as SNPK>NPK>25%M>50%M>75%M>100%M>CK.The emission factor of different treatments showed that NPK treatment had the highest emission factor,significantly higher than the manure amendment treatments and SNPK treatment.Additionally,with the increasing of manure N substitution,the emission factor gradually decreased,especially for 75%M and 100%M treatments with the lowest values.In conclusion,DNDC model can successfully simulate crop yield and N₂O emission with combination of organic and chemical fertilization under wheat and maize rotation system in Guanzhong Plain.The results both from field experiment and long-term simulation of DNDC model showed that the substituting 75%chemical N by organic manure can not only ensure the yield stability of wheat and maize cropping systems and also reduce the accumulation of soil nitrate N in soil profile and N gases emissions.Hence,75%M treatment is the best combination of organic manure and chemical fertilizer under wheat and maize rotation system in this area.