| Straw returning is not only an important way to fertilize soil,but also a vital guarantee for high and stable crop yield.However,the high C/N of straws may lead to crop yield reduction for the nitrogen competition between microbes and crops.Therefore,it is of great significance to strengthen the study of nitrogen application model with straw returning for regulating soil C/N,improving N supply,increasing crop yield and nitrogen use efficiency.The fixed position experiments of rice field in Jiangxi Province and corn field in Henan Province were conducted,in order to investigate the effects of different basal-topdressing N ratio(4:6,6:4 and 8:2 for rice season,respectively and 1:1,1:1.5 and 1:2 for maize season,respectively)with rice/wheat straw returning on crop yield,nitrogen use efficiency,soil physicochemical parameters,extracellular enzyme activity and microbial community structure.The results were showed as follows:1.Effect of nitrogen application model with straw returning on crop yield and nitrogen fertilizer utilization efficiency.The highest rice yield was recorded under the model of base to topdressing ratio of N at 6:4 with straw returning,which was 20.08% higher than that of single N treatment,and the nitrogen use efficiency increased by 8.23 percentage points.The highest maize yield was observed under the model of base to topdressing ratio at 1:1 with straw returning,which was 9.98% higher than that of single N treatment,and the nitrogen use efficiency increased by 5.75 percentage points.2.Effect of nitrogen application model with straw returning on soil physicochemical properties.Compared with the single N treatment,the treatments that different basal-topdressing N ratio with straw returning significantly increased the contents of soil organic matter and total nitrogen,also increased the contents of soil nitrate nitrogen,ammonium nitrogen,available potassium and available phosphorus as well as adjusted the soil pH value,especially for the model of straw returning with base to topdressing ratio of N at 6:4 and 1:1 for rice season and maize season,respectively.3.Effects of nitrogen application model with straw returning on extracellular enzyme activities.Compared with the single N treatment,the treatments that different basal-topdressing N ratio with straw returning significantly increased the enzymes activities of ?-glucosidase,cellobiose,?-xylosidase,?-glucosidase,aminopeptidase,phenol oxidase and peroxidase.Except for phosphatases,the other extracellular enzyme activities were the highest under the model of straw returning with basal-topdressing N ratio at 6:4 and 1:1 for rice season and maize season,respectively.4.Effects of nitrogen application model with straw returning on soil microbial community structure.Compared with the single N treatment,the treatments that different basal-topdressing N ratio with straw returning significantly increased the richness and diversity of soil bacteria,especially for straw returning with base to topdressing ratio of N at 6:4 and 1:1 for rice season and maize season,respectively.The dominant bacterial phyla in rice season were Proteobacteria,Acidobacteria?Nitrospira and Actinobacteria,respectively.While,Proteobacteria,Actinobacteria,Acidobacteria and Chloroflexi were the most abundant phyla in maize season,respectively.LEfSe analysis showed that the highest LDA values were Actinobacteria and Proteobacteria in rice season and maize season,respectively.Canonical correspondence analysis showed that soil pH(P=0.028),organic matter(P=0.042),total nitrogen(P=0.038)in the tillering stage and organic matter(P=0.02),total nitrogen(P=0.046),available potassium(P=0.019)in the mature stage had significant effects on bacterial community structure in rice season,respectively.Whereas,soil pH(P=0.002),organic matter(P=0.004)in the silking stage and soil pH(P=0.03),nitrate nitrogen(P=0.036),available potassium(P=0.044)in the mature stage had significant effects on bacterial community structure in maize season,respectively.In conclusion,rational nitrogen application model with straw returning could not only significantly increase crop yield,nitrogen use efficiency,organic matter and total nitrogen content,but also regulate soil pH,enhance enzyme activities of carbon and nitrogen hydrolase and oxidase and improve soil microbial community structure.Straw returning with base to topdressing ratio of N at 6:4 and 1:1 were the optimal model for rice season and maize season,respectively. |
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