Effect Of Biochar-Based Conditioner On Nitrogen And Phosphorus Retention From Soil And On Phosphate Adsorption From Aqueous Solutions

Nowadays,a crucial issue in agricultural non-point source pollution is how to reduce the loss of nitrogen?N?and phosphorus?P?from soil and water,and phosphorus is the primary control factor of eutrophication.Therefore,the development of conditioning agents for preventing the phosphorus loss has become a research focus.This research aimed at developing new conditioner for non-point source pollution.Firstly,three kinds of widely used soil conditioners?anionic polyacrylamide,biochar,peat soil?combination were applicated through the greenhouse leaching experiment to explores the synergistic effects of different soil conditioners on N and P retention under two irrigation modules:spray and drip irrigation,and selected the optimal combination of conditioner used for P retention.After that,two kinds of biochar-based conditioner?PSBC and PMBC?that derived from rice straw biochar and sheep manure biochar were explored on phosphate adsorption and adsorption behavior.The main research conclusions are as follows:?1?The significance influence order of the of three soil conditioners on the leachate volume is PAM>peat soil>biochar,among which PAM had a very significant influence.Under sprinkler irrigation and drip irrigation,the optimal application level combinations of three conditioners for soil water retention were 2 g·kg^-1 of PAM,20 g·kg^-1 of peat soil,and 10g·kg^-1 of biochar;2 g·kg^-1 of PAM,10 g·kg^-1 of peat soil,and 40g·kg^-1 of biochar,respectively.?2?The conditioner combination P₂S₂B₃(2 g·kg^-1 of PAM,10 g·kg^-1 of peat soil,and 40g·kg^-1 of biochar)could achieve the highest amounts of P retention under two irrigation modules.The highest amounts of P retention under sprinkler irrigation was 11.88mg·kg^-1 and this number for drip irrigation was 7.47 mg·kg^-1.The conditioner combination P₂S₃B₁(2 g·kg^-1 of PAM,20 g·kg^-1 of peat,and 10g·kg^-1)achieved the highest amounts of N retention under two irrigation modules.The cumulative N retention amount under sprinkler irrigation was 83.12 mg·kg^-1,and this number under drip irrigation was 50.09 mg·kg^-1.?3?The order of retention ability of the three soil conditioners on P was PAM>biochar>peat soil.The SEM results showed that increasing PAM could increase the number of soil aggregates and enhance the water holding capacity of soil.At the same time,the combined application of PAM and biochar helps to increase the pore volume of biochar and soil,so as to enhance its adsorption and retention on phosphorus.?4?Both the application of biochar and biochar combined with PAM increased the leachate pH from soil under soil column leaching experiment.The application of 4%rice straw biochar or 4%sheep manure biochar increased the phosphorus concentration of leachate from 3 soils to varying degrees?p<0.05?,and then decreased.But the application of biochar combined with PAM decreased the phosphorus concentration of leachate from 3 soils,and the reduction rate were 31.1%?61.8%,31.65%?50.0%and 30.5%?47.9%,respectively.?5?Biochar-based conditioner was prepared based on two kinds of biochar.The adsorption results of phosphate showed that the two biochar-based conditioners modified by PAM had higher specific surface area and total pore volume,and its adsorption capacity on phosphate was better than that of biochar.The batch adsorption studies displayed that adsorption kinetics data of biochar and surface modified biochar fitted very well pesudo-second-order kinetic model and the isotherm adsorption data fitted well the Freundlich isotherm model.The maximum adsorption capacities of PSBC and PMBC were 22.41 mg P/g and 12.08 mg P/g respectively,which were higher than that of SBC?14.67 mg P/g?and MBC?9.04 mg P/g?.FTIR analysis shows that the adsorption of phosphate by two biochar and biochar-based conditioners were surface adsorption processes dominated by chemical adsorption,and the oxygen-containing functional groups play an important role.In addition,this study shows that the adsorption of phosphate by several biochar and biochar-based conditioners was highly correlated with pH value,and the presence of calcium ions will enhance the adsorption capacity of biochar-based conditioners on phosphate.