Effects Of Straw Returning And Nitrogen Application On Soil Nutrients And Microbial Community Structure In Typical Black Soil Region

Long-term single application of chemical fertilizers has led to a decline in black soil fertility of the Northeast China,while straw returning has been advocated to increase soil fertility.However,the influences of different N fertilizer rate on physical and chemical soil properties and microbial diversity under long-term straw returning in the black soil are still unclear,and the differences in extracellular enzyme activities and soil microbial community response still urgently require in depth and systematic research.In this study,a specific-site experiment was conducted in 2017-2021 with different N fertilizer application rate(0,70,140,210,280 and 350 kg/hm~2)under the conditions of straw returning and removing,to investigate the effects of N fertilizer application on maize yield and nutrient uptake,to explore the response mechanism of soil enzyme activity and microbial community structure.The main conclusions are as follows:(1)Straw returning with reasonable nitrogen fertilizer application can improve soil available nutrients and alleviate soil acidification process.Straw returning significantly increased soil total nitrogen,organic carbon and available potassium content.The mean values of total nitrogen,soil organic carbon and available potassium content in the 0-20 cm soil layer of maize at harvesting stage increased by 9.26%,13.30%and 23.93%in the straw returning treatment compared to the straw removing treatment.Soil p H decreased with the increase of nitrogen application,for the 0-20 cm soil layer,the N350 treatment reduced by 17.59%,13.53%and 8.82%under the straw removing treatment compared to the N0 treatment for maize at the elongation,filling and harvesting stages,and the SN350 treatment reduced by 11.04%,5.65%and 6.96%under the straw returning treatment compared to the SN0 treatment for maize at the elongation,filling and harvesting stages,but the decrease in p H of the straw returning treatment was lower than that of the straw removing treatment,indicating that straw returning has the effect of alleviating soil acidification to a certain extent.(2)Straw returning with reasonable nitrogen fertilizer application can improve maize yield and nitrogen use efficiency.The highest mean yields were obtained at the N application rate of210 kg/hm~2 and 280 kg/hm~2 under straw returning and removing conditions,respectively,and the former increased by 325.76 kg/hm~2 compared to the latter.When obtaining the highest yield,the cumulative N agronomic efficiency,cumulative N recovery efficiency and cumulative N partial productivity of the straw returning treatment increased by 10.25 percentage points,4.29kg/kg and 15.70 kg/kg,respectively,compared to the straw removing treatment.Using 95%confidence interval of the nitrogen application rate obtained when the theoretical surplus ratio is 0,and taking into account three aspects of nitrogen uptake,yield and nitrogen surplus ratio,it is calculated that the threshold value of nitrogen fertilizer input under straw returning in study region is 181.19-200.27 kg/hm~2.(3)Straw returning with reasonable nitrogen fertilizer application can significantly improve the soil extracellular enzyme activities.The mean values ofβ-glucosidase,cellobiose hydrolase,β-N-acetamidoglucosidase and phosphatase activities in the 0-20 cm soil layer of maize at harvesting stage increased by 46.17%,87.87%,19.66%and 18.71%in the straw returning treatment,and by 71.77%,119.99%,110.95%and 29.51%in the 20-40 cm soil layer compared with the straw removing treatment.The enzyme activity ofβ-glucosidase was higher at 210 kg/hm~2 of nitrogen application rate and decreased when the nitrogen application rate exceeded 210 kg/hm~2.(4)Straw returning with reasonable nitrogen fertilizer application can change microbial community structure.Long-term single application of chemical fertilizer significantly reduced the richness and diversity of the microbial community.The 0-20 cm soil bacterial Chao1 index N280 treatment decreased by 19.01%,20.01%and 6.56%compared to the N0 treatment at the elongation,filling and harvesting stage stages of maize,and the 0-20 cm soil fungal Chao1index N280 treatment decreased by 9.61%and 16.06%compared to the N0 treatment at the elongation and harvesting stage stages of maize.There was no significant difference in the composition of the soil microbial community at the phylum level in different maize growth stages,and the dominant species with higher relative abundance were consistent,but the relative abundance of the dominant taxa changed under each fertilizer application treatment.The phyla Actinobacteria and Proteobacteria were the dominant bacterial groups in the tested soils,while the phyla Ascomycota and Basidiomycota were the dominant fungal phyla in the tested soils each treatment.