Preparation Of Magnesium Modified Biochar At Different Pyrolysis Temperatures And Its Effect On Soil Chemistry Properties And Enzyme Activity

Biochar has been widely studied in recent years for its importance in soil improvement,fertiliser innovation and greenhouse gas reduction.The structural and physicochemical properties of modified biochar have been improved,and its effect on soil fertility can be improved to different degrees.In order to investigate the mechanism of the effect of Mg-modified biochar with different physicochemical structures on soil properties,Mg-modified biochars were prepared from rice and maize straw and the effect of different pyrolysis temperatures(300°C,400°C,500°C and 600°C)on the structure and physicochemical properties of Mg-modified biochar were investigated.Mg-modified biochar was mixed thoroughly with soil at 1%(w/w)addition level for indoor simulated soil tests.Soil chemical properties were measured on60 th,120th and 180 th days of incubation,and soil enzyme activity and soil microbial biomass carbon and nitrogen content were measured on 180 th day.The investigation of the effects of Mg-modified biochar on soil chemical properties,enzyme activity and microbial biomass carbon and nitrogen would help to improve the added value of waste agroforestry resources on the one hand,and provide the necessary theoretical basis and scientific basis for its application in soil and subsequent research on the other hand.The main conclusions are as follows.(1)The high p H,C(%)content and rich pore structure as well as the large specific surface area of the Mg-modified biochar from rice and maize straw are advantageous for acidic soil amendment.As the temperature increased,the p H,ash,specific surface area,pore volume and C(%)content of the Mg-modified biochar increased,while the yield,H(%),N(%),O(%)content and functional groups such as-OH,C=O,-COOH and-CHO decreased,and the aromaticity and hydrophobicity increased but the polarity decreased.Compared to unmodified biochar,Mg-modified biochar has more-OH and-COOH functional groups.The pore types of the Mg-modified biochar were mainly slit pore,and the higher temperatures favoured the formation of micropores and smaller mesopores in the rice straw Mg-modified biochar,but not mesopores and macropores,whereas for the maize straw Mg-modified biochar,the higher temperatures promoted the development of both micropores,mesopores and macropores.At the same time,higher temperature can promote the formation of different types of mineral salts on the surface or inside the Mg-modified biochar.(2)Indoor simulated soil experiments showed that the addition of Mg-modified biochar could reduce soil acidity and improved soil fertility.Compared to the control group,Mg-modified biochar treatment significantly increased the contents of soil available potassium,available phosphorus,total phosphorus,organic carbon and exchangeable calcium and magnesium,and effectively increased the content of total nitrogen.Comparing the effects of the two Mg-modified biochar treatments on soil improvement,the Mg-modified biochar treatment of rice straw was more effective in increasing soil available potassium,available phosphorus,total phosphorus and exchangeable magnesium,while the Mg-modified biochar of maize straw was more effective in increasing soil organic carbon and exchangeable calcium content.(3)As the pyrolysis temperature varied from 300 to 600°C,the contents of available potassium,available phosphorus,total phosphorus and p H of the soils treated with Mg-modified biochar showed an increasing trend,while the contents of alkaline dissolved nitrogen,exchangeable calcium and magnesium and microbial biomass nitrogen showed a decreasing trend.It can be seen that the Mg-modified biochar with high pyrolysis temperature promoted the contents of available potassium,available phosphorus and total nitrogen better,while the Mg-modified biochar with low pyrolysis temperature promoted the content of soil alkaline dissolved nitrogen,exchangeable calcium and magnesium and microbial biomass nitrogen better.As the incubation time in the simulated soil increased,the available potassium content of the soil treated with Mg-modified biochar from rice straw tended to increase and then decrease,while the available phosphorus content tended to increase and the organic carbon and exchangeable magnesium content tended to decrease.Soils treated with Mg-modified biochar from maize straw showed an increasing trend in available phosphorus,total phosphorus and exchangeable magnesium,and a decreasing trend in available potassium and organic carbon.(4)Mg-modified biochar had a large effect on soil urease activity,with some treatments increasing urease activity.The MCBC-500 treatment was the most effective in increasing soil urease activity.While the overall effect of straw Mg-modified biochar application on soil ?-glucosidase and acid phosphatase activities was not significant,but MCBC-600 treatment significantly enhanced soil ?-glucosidase activity by 6.7% compared with the control and the MCBC-400 and MCBC-600 treatments significantly enhanced soil acid phosphatase activity by 11.2% and 7.1%,respectively.(5)The effects of Mg-modified biochar on soil microbial biomass carbon and nitrogen were different for rice and maize straw.The addition of Mg-modified biochar reduced soil microbial biomass carbon content by 1.8% to50.9%,but had an increasing effect on microbial biomass nitrogen content,with significant increases of 256.2% and 161.4% for MRBC-300 and MCBC-400 treatments,respectively.The correlation results showed that soil p H and microbial biomass carbon and nitrogen content and urease activity were significantly correlated,soil total nitrogen was significantly correlated with?-glucosidase activity and acid phosphatase activity,and soil organic carbon was significantly correlated with urease activity and microbial biomass nitrogen content.