Research On Soil Nutrient Stoichiometric Balance Based On Biochar Compensation

Soil degradation,represented by soil nutrient decline,is becoming more and more serious in China.Soil quality is facing a great challenge.Biochar,as an emerging environment-friendly carbon-based biological material,has a broad application prospect in the remediation of degraded soil.In this study,biochar was used as a slow-release fertilizer in soil conditioning.The individualized fertilization scheme of different soils was determined by the data statistics and model construction and balance calculation of soil nutrient stoichiometry,so as to guide the rational application of fertilizers and provide a certain theoretical basis for nutrient compensation of degraded soil.Through yield calculation and element analysis,the optimal carbon temperature was determined,and the carbon sequestration and nutrient resources of biochar were estimated to show its field application prospect.The results showed that the yield,hydrophilicity and polarity of biochar were negatively correlated with pyrolysis temperature,while the degree of aromatization was positively correlated with pyrolysis temperature.In 2017.the total estimated annual nutrient resources of maize straw biochar and chicken manure biochar in China was up to 6.76×107 t.The release kinetics experiment was conducted to analyze the soluble nutrient release of biochar,and the nutrient release mechanism of biochar was discussed by combining the quasi-first and quasi-second kinetics models.The results showed that R2 obtained by quasi-second-order kinetic model fitting was closer to 1 in the kinetic study on the release of soluble nitrogen and soluble potassium of corn stalk biochar and chicken faecal biochar,indicating that the reaction process was a chemical reaction accompanied by changes in chemical bonds.The reaction rate constant less than 1 indicates that the reaction is rapid.The quasi-first kinetic model fitting effect of soluble phosphorus in the two biochar materials was better,indicating that the reaction was dominated by physical process and was a dissolution process of phosphate in biochar.Biochar can be used as a fertilizer to supplement nutrient contents of N,P and K lacking in soil.In this paper,a soil nutrient stoichiometric balance model was constructed,and the individualized fertilization scheme of different soils was given by combining the soil basic fertility and the nutrient content provided by biochar.Risk assessment of soil heavy metal contamination was also carried out for these programmes.The results showed that in the single element conditioning plan,when biochar was applied to supplement the deficiency of three soil nitrogen elements,most of the plans resulted in the excessive P element in the soil and the environmental risk.When biochar was applied to supplement the phosphorus deficiency in the three soils,additional nitrogen fertilizer was needed,and 13.07%～92.24% of nitrogen fertilizer and 100% of phosphorus fertilizer and potash fertilizer could be reduced.When biochar is used to regulate soil potassium,additional chemical fertilizers are needed to supplement N and P elements in the three soils,and nitrogen,phosphorus and potash fertilizer were reduced by 4.56%～62.19%,32.17%～67.42% and 100% respectively.At the same time,the field application of biochar has not been found to have a potential risk of heavy metal pollution.