Stability Of Soil Colloid And Its Adsorption Characteristics Of Tetracycline Under Different Fertilization

Analyzing the stability of soil colloid and its ability to adsorb tetracycline from farmland soil under different fertilizations would help provide a theoretical basis for clarifying the colloid facilated-migration of tetracycline in soil.In our study,the soil particles were divided into three fractions:0.053-2 mm,2 ?m-0.053 mm and<2?m(Soil colloid),respectively.The soil fertilization treatments were without fertilization(CK),chemical fertilizers only(NPK)and organic manure(OF).The dispersion stability of different soil colloids was analyzed by combination of static sedimentation method and dynamic light scattering technique.The kinetics of soil colloid under different electrolyte conditions was investigated.The effect of different electrolyte solutions on the surface potential of soil colloid was determined by zeta potential analyzer.Finally,the adsorption capacity,kinetics and isotherm of tetracycline on soil with different particle size were analyzed by batch adsorption method.Our main results showed that:1.The application of chemical fertilizers and organic fertilizers could reduce the release of soil colloid.However,the application of organic manure was more favorable for the formation of large aggregates.The sedimentation rate of soil colloid followed the order CK>NPK>OF in the sedimentation method,and the sedimentation ratio had the same pattern.2.The application of organic manure could increase the content of large aggregates in soil and decrease the release of colloid.The released colloid content was highest in CK,The colloid in CK was easier to deposit and possessed the lowest stability.The critical coagulation concentration(CCCcaCl2)of soil colloid was in the order of OF>NPK>CK indicating that the application of organic fertilizer will increase the soil colloid in the water.This result is consisted with the finding of sedimentation method.3.The cation valence is important for stability of soil colloid,but the effects of anion species and valence are not significant.The addition of electrolyte can reduce the zeta potential of the soil colloid,and then promote the soil colloid coagulation.For the soil colloid from OF treatment,the particle size was smaller,the zeta potential was higher and the adsorption capacity of tetracycline was stronger compared to soil colloids in other treatments.4.The adsorption capacity of tetracycline in the soil in OF treatment was higher than other treatments.Among various particle sizes,soil colloid from OF treatment had the highest adsorption capacity towards tetracycline.Therefore,the application of organic fertilizer can effectively reduce the release of colloid in soil.Meanwhile,it can also improve the stability of colloid in water and the adsorption capacity for tetracycline,thus affecting the distribution and migration of pollutant tetracycline in soil structure.