| China is an agricultural country with rich crop straw resources.Crop straw contains a lot of nitrogen,phosphorus,potassium and other nutrient.Crop straw returning can improve soil structure,enhance soil fertility and increase crop yield.In recent years,biochar as a new type of soil amend,widely used in agriculture.It is of great significance to study the similarities and differences between straw returning and biochar application to soil and crops,and to explore the model of high-efficiency straw returning to field.Application rates of N fertilizer were designated as 0,150 and 300 kg N ha-1(N0,N150 and N300),with three treatments(CK;crop straw returning,S;biochar application,B)were implemented in this experiment to explore the effects of nitrogen fertilizer and straw returning and biochar application on soil nutrients,soil carbon pool and cotton nutrient uptake.The main results were as follows:1.Effects of straw and biochar on soil physical and chemical properties and cotton nutrient uptake under different nitrogen ratesStraw returning and biochar returning had no significant effect on soil total nitrogen content.They could improve soil water content,soil ammonium nitrogen,available phosphorus and available potassium content,reduce soil bulk density,soil salt content and nitrate nitrogen content,and buffer soil pH,and the two-year trend was basically the same.By analyzing the source of soil nutrient variation,the way of straw returning to the field had a significant impact on soil total nitrogen,available nitrogen,available phosphorus and available potassium.The interaction between straw returning and nitrogen application had no significant effect on soil nutrients.Both straw returning and biochar returning combined with nitrogen fertilizer could significantly increase cotton biomass accumulation.The increase of cotton biomass is mainly due to the increase of soil available P and available K content,and the increase of plant phosphorus accumulation has a significant effect on the improvement of plant biomass.By analyzing the variation sources of cotton biomass and nutrient uptake,the inter-annual changes have a very significant impact on cotton biomass,nitrogen,phosphorus and potassium uptake.The way of straw returning to the field had significant or extremely significant effects on cotton biomass and plant P and K uptake.The interaction between straw returning and nitrogen application had no significant effect on cotton biomass and nitrogen,phosphorus and potassium uptake by cotton plants.2.Effects of straw and biochar on soil carbon pool and soil enzyme activity under different nitrogen ratesBoth straw returning and biochar returning combined with nitrogen fertilizer increased the contents of soil organic matter,water-soluble organic carbon,microbial biomass carbon and oxidizable organic carbon,and mainly increased the total organic matter content and soil carbon pool-index by increasing the content of soil active organic carbon.The effect of biochar on organic matter,water-soluble organic carbon,oxidizable organic carbon and soil carbon pool index was greater than that of straw,and the effect of straw on microbial biomass carbon was better than that of biochar.Based on the analysis of variation sources of soil organic carbon components,inter-annual changes have significant or extremely significant effects on soil organic matter,water-soluble organic carbon and microbial biomass carbon,and the interaction between straw returning and nitrogen application has significant effects on soil organic matter.Straw returning and biochar returning could improve soil invertase,urease and alkaline phosphatase activities,and the effect of straw returning was better than biochar,but had no significant effect on catalase activity.Under straw and biochar returning,soil alkaline phosphatase and urease promoted soil nutrients and organic carbon pool components mainly directly,while catalase and invertase mainly indirectly. |
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