| Biochar has significant effects on soil nitrogen and crop nitrogen use.However,biochar aging in farmland environment(temperature,water,root exudates,soil,etc.)will change the effect of biochar on nitrogen utilization.Therefore,this study began with the aged analysis of cotton straw charcoal(hereinafter referred to as cotton stalk charcoal)to explore the characteristics of different aged cotton stalk charcoal and its effect on ammonia volatilization,leaching loss of nitrogen in soil and nitrogen utilization in crops.The main conclusions are as follows:(1)Dry-wet alternation,freeze-thaw cycle,citric acid and 6 years of field treatment all affected the physical and chemical properties of cotton stalk charcoal.Compared to fresh cotton stalk charcoal,the changes of structure and properties of different aged cotton stalk charcoal are as follows: the p H value and electrical conductivity decreased,the contents of total phosphorus and total potassium decreased,the surface oxygen-containing functional groups increased,and the content of total nitrogen,specific surface area and pore diameter changed;the structure and properties of citric acid aged cotton stalk charcoal were the most obvious,the p H value and electrical conductivity decreased by 5.14 units and 7.31 m S/cm,the total nitrogen content increased by 7.8%,and the specific surface area,total pore volume and mesoporous volume increased by 1.88,1.37 and 1.36 times.(2)The fresh and different aged cotton stalk charcoal were mixed with aeolian sand at 2% mass ratio,and Urea(three nitrogen application levels: 0,200 and 400mg/kg)was applied to the surface layer.The indoor static soil ammonia volatilization culture experiment showed that: at the N200 and N400 levels,compared with that without cotton stalk charcoal treatment,the ammonia volatilization accumulation of fresh and different aged cotton stalk charcoal treatments increased by 47.6%-126.2% and 14.0%-83.0%,respectively.Compared with the fresh cotton stalk charcoal treatment,the ammonia volatilization accumulation of different aged cotton stalk charcoal treatment decreased,and the citric acid aged cotton stalk charcoal treatment significantly decreased 34.7% and 37.7%,which had a relatively strong inhibition effect on ammonia volatilization in soil.(3)Used laboratory soil column simulation test,studied on effects of different aged cotton stalk charcoal on soil nitrogen leaching under nitrogen added treatment at 0 、 200 and 400mg/kg nitrogen application levels.The results show that: compared with the without adding cotton stalk charcoal treatment,under different nitrogen application levels,fresh and different aged cotton stalk charcoal treatments increased the soil nitrogen leaching loss;but compared with the fresh cotton stalk charcoal treatment,the soil nitrogen leaching loss of different aged cotton stalk charcoal treatment were reduced,at the N200 level,the total nitrogen cumulative leaching loss of citric acid aged cotton stalk charcoal treatment was the least,which decreased by 30.8%,and at the N400 level,the total nitrogen cumulative leaching loss of dry-wet aged cotton stalk charcoal treatment was the least,which decreased by 11.2%.(4)In the aeolian sand soil-wheat planting system,under different nitrogen application levels,soil total nitrogen content of different aged cotton stalk charcoal treatments was higher than that of fresh cotton stalk charcoal treatments and untreated cotton stalk charcoal treatments,while soil p H value and electrical conductivity were higher than that of untreated cotton stalk charcoal treatments and lower than that of fresh cotton stalk charcoal treatments.The interaction of low nitrogen fertilizer(N200)with fresh and aged cotton stalk charcoal promoted dry matter accumulation and nitrogen use efficiency of wheat,and the nitrogen uptake efficiency of citric acid aged cotton stalk charcoal was the highest.When high nitrogen fertilizer(N400)interacted with fresh and aged cotton stalk charcoal,the dry matter quality of wheat was decreased and excessive nitrogen fertilizer application inhibited the growth of wheat,reduced the nitrogen use efficiency of wheat.N absorption efficiency of wheat under N200 level was significantly higher than that under N400 level.In conclusion,the interaction between cotton stalk charcoal and low nitrogen(200mg/kg)has good economic and productive benefits,compared with fresh cotton stalk charcoal treatment,dry-wet alternate,freeze-thaw cycle and citric acid aged cotton stalk charcoal treatment reduced soil ammonia volatilization and nitrogen leaching loss,and increased nitrogen use efficiency of wheat,and the citric acid aged cotton stalk charcoal treatment had the highest nitrogen use efficiency. |
