Study On The Adsorption Effect Of Biochar On Nitrogen And Phosphorus And Its Fertilizer Application

In China’s agricultural production,there are problems such as excessive input of nitrogen and phosphorus fertilizers and low fertilizer utilization efficiency.Nutrients that are not absorbed by crops are lost through surface runoff,underground leakage,and dry and wet deposition,causing environmental pollution to ecosystems such as soil,water,and atmosphere.Due to its well-developed pore structure,huge specific surface area,and high stability,biochar is widely used to reduce water eutrophication,improve soil quality,increase crop yields,and control greenhouse gases emissions.However,the physical and chemical properties of biochar are quite different because of the different raw materials.Therefore,the study of the physical and chemical properties of biochar from different sources and the adsorption of nitrogen and phosphorus provides a scientific basis for the resource utilization of agricultural waste and the reduction of nitrogen and phosphorus pollution,and the development of biochar-based organic fertilizer with biochar as the carrier also opens up new ideas for the application of biochar and the sustainable development of agricultural production.In this paper,attapulgite rice hull biochar composite,rice hull biochar and sludge biochar are used as raw materials to study their physical and chemical properties such as pH,element composition,specific surface area,pore structure and functional group structure,and explore the adsorption mechanism of three kinds of biochar for ammonium nitrogen and phosphate under different pH conditions,reaction time and initial concentration conditions.The biochar-based organic fertilizers were made by attapulgite rice hull biochar composite,rice hull biochar,and sludge biochar as carriers,to study its effects on tomato growth and soil physical and chemical properties in greenhouse.The main conclusions are as follows:(1)The three types of biochar are all alkaline.The content of nitrogen and biochar in rice hull biochar is the highest,the H/C value is the smallest,and the aromaticity is the highest.The attapulgite rice hull biochar composite has the largest specific surface area,and the smallest pore size.The attapulgite rice hull biochar composite and rice hull biochar both have a rough surface tubular structure with developed pore structures and rich functional groups.The pore structure of sludge biochar is a wedge-shaped pore structure formed by the accumulation of flake particles.The total pore volume and pore diameter are the largest.The adsorption/desorption isotherms of attapulgite rice hull biochar composite,rice hull biochar,and sludge biochar all belong to type Ⅳ,with H3 type hysteresis loop.(2)The results of adsorption test show that,pH,reaction time and initial concentration all affected the adsorption effect of biochar on ammonium nitrogen and phosphate.The maximum adsorption capacity for ammonium nitrogen was 5.18 mg·g-1 in rice hull biochar treatment,with the condition of pH 7,180 min reaction time,and 100 mg·L-1 initial concentration.The adsorption behavior conformed to the pseudo-second-order kinetic equation and the Langmuir isotherm equation.The best adsorption effect on phosphate,and the largest adsorption capacity can reach 30.31 mg·g-1 in the attapulgite rice hull biochar,when the pH is 5,the reaction time is 720 min,and the initial concentration is 150 ng·L-1.The pseudo-first-order kinetic equation and Freundlich isotherm equation can better fit the adsorption behavior of phosphate.(3)The results of pot experiment showed that,the biochar-based organic fertilizer significantly improved the physical and chemical properties of soil,increased enzyme activity,promoted the development of chlorophyll content,and improved tomato yield and quality.Compared with the conventional fertilizer treatment,the attapulgite biochar-based organic fertilizer treatment significantly increased soil pH value,total nitrogen,available potassium content,and soil urease and catalase activities,whereas the rice hull biochar-based organic fertilizer treatment significantly increased soil total nitrogen and organic matter contents and increased soil acid phosphatase and sucrose enzyme activities.Compared with the conventional fertilizer treatment,the rice hull biochar-based organic fertilizer treatment was more conducive to the accumulation of chlorophyll in tomato plants,thereby increasing the tomato yield by 14.9%.The amount of nitrogen absorption was also increased by 8.47%in plants under rice hull biochar-based organic fertilizer treatment.In tomato plants grown under the rice hull biochar-based organic fertilizer and sludge biochar-based organic fertilizer treatments,the contents of VC,soluble sugar,and nitrate increased by 16.5%and 19.5%,14.7%and 12.1%,and 36.9%and 34.9%respectively,and the soluble solid content of tomatoes grown under attapulgite biochar-based organic fertilizer and rice hull biochar-based organic fertilizer treatments increased by 14.8%and 25.9%compared with that of the tomatoes grown under the conventional fertilizer treatment.Based on the comparative analysis of soil physical and chemical properties,tomato chlorophyll content,plant nitrogen uptake,tomato yield and quality,rice hull biochar-based organic fertilizer was the best,followed by attapulgite biochar-based organic fertilizer.In summary,rice hull biochar has a relatively functional group structure and better adsorption performance.When the pH is 7,the reaction time is 180 min,and the initial concentration is 100 mg·L-1,it has a better adsorption effect on ammonium nitrogen.It is an ideal material for the development of biochar-based organic fertilizer products.Moreover,rice hull biochar-based organic fertilizer developed in this project is more suitable for improving the soil of facility tomato cultivation,while promoting the excellent growth of tomatoes,improving tomato nutrient absorption,and providing a reference scientific basis for the control of nitrogen and phosphorus pollution in farmland.