Study On Biochar Returning By Biochar Prepared Under Different Pyrolysis Temperatures And Atmospheres

Biochar,containing large amounts of carbon,macro or micro-nutrients and porous structure,is the solid product obtained by pyrolyzing biomass at complete or partial exclusion of oxygen.Various common residual forms of the biomass can be utilized as a feedstock for the preparation of biochar.In recent years,there is a growing interest applying biochar to improve agricultural soil.However,study shows that preparation conditions?temperature,atmosphere,raw material,pyrolysis rate,etc?will directly affect the physicochemical properties of biochar.At present,many uncertainties exist in defining “biochar quality”,less attention has been paid on the effect of biochar returning and their own nitrogen supply.Given this,This article chose rice straw and 15 N labelled wheat straw as the feedstock to prepare biochars under different atmospheres?N2 and CO₂?and pyrolysis temperatures,and characterized the products through biochar yield calculation,elemental analysis,FESEM-EDS,BET specific surface,EA-IRMS and other analysis methods to figure out the effect of preparation condition on the regulation of biochar physicochemical properties,investigated the the effect after biochar returning on plant growth through the pot experiment,and discussed the regulation of biochar own nitrogen supply on plant growth with 15 N tracer method,which was expected to provide a theoretical reference for the preparation condition of high-quality biochar and its reasonable use in agriculture.The main results we have achieved are as follows:?1?At the same pyrolysis atmosphere,the yield and nutrient elements of the rice straw-derived biochar decreased,but the pH,total pore volume and specific surface area increased with an increase of pyrolysis temperature,the raw rice straw could not be pyrolyzed completely at 300 ?,char structure gradually developed,more developed pore structure in biochars prepared at intermediate temperate?400??and a collapse was seen in high temperatures?800??.Mesopores were the dominant pores in all the rice straw-derived biochars,which can reach its peak at 400 ?,while micropores and macropores will get a maximum at 800 ? and 600 ?,respectively.At the same pyrolysis temperature,CO₂ prepared biochars exhibited a better nutrient characteristics and pore structure than N2 prepared biochars.?2?The results of the pot experiment showed that the porous structure and specific surface area of biochar enhances its soil porosity,soil particles attached on the surface of biochar or into its pore structure,which can reduced the compressive force of soil particles,thus improved soil physical properties.Available soil nutrients and pH were improved with the addition of biochars to different degrees,plant growth in the biochar treatments was better than in the control treatment,indicating the positive effect of biochars returning on plant growth.Plants performed well at 400°C prepared biochar returning for its higher nutrient content rather than the 800°C prepared biochar.Plant growth in the BC treatments was much better than that in the BN treatments,the higher pH in the BC treatments indicated stronger nitrification,which favoured plant growth.The best effect can obtain at the 400°C and CO₂ prepared biochar returning.?3?The results of pot experiments carried out by 15 N labeled wheat straw biochar showed that a certain amount of nitrogen could release after biochar rerurning.Pyrolysis temperature and atmosphere affected biochar nitrogen supply.Biochar prepared at 400°C and CO₂ can provide more nitrogen by its own supply and promoting N release of soil to plants,which contributed to the remarkable dry matter accumulation of plants.