| Soil dissolved organic carbon(DOC)can be adsorbed by soil colloids and minerals to increase its stability.DOC is also one of the important sources of soil organic carbon.Studying the adsorption and desorption characteristics of DOC in different soils under different fertilization conditions is of great significance for maintaining and improving soil productivity,maintaining the stability of agricultural ecosystems,and rational fertilization of farmland soils.Based on the long-term fertilization test platform of Shenyang brown soil and Qiyang red soil,this study selected four long-term fertilization treatments,no fertilizer(CK),single application of organic fertilizer(M),application of chemical fertilizer(NPK),and combined application of organic fertilizer(NPKM).Using indoor kinetic adsorption,isothermal adsorption and isothermal desorption experiments,combined with three-dimensional fluorescence spectroscopy,the adsorption-desorption characteristics of two different sources of DOC(fresh pig manure and fresh forest soil)on brown soil and red soil treated with long-term different fertilization were analyzed and the main controlling factor.The main results are as follows:(1)The adsorption capacity of DOC in different soils varies with the adsorption time as follows: it increases rapidly in the first 2 hours of adsorption,slows down in 2-6 hours,and reaches equilibrium in about 12 hours.The quasi-first-order kinetic equation,the quasi-second-order kinetic equation and the parabolic diffusion equation can all be used to fit the kinetic adsorption characteristics of soil to DOC,and the quasifirst-order kinetic equation and the quasi-second-order kinetic equation have good fitting effects.Based on the parabolic diffusion equation,it shows that the fast adsorption stage of soil to DOC is diffusion adsorption,and the slow adsorption stage is chemical adsorption.(2)Different soils have the same isotherm adsorption trend for DOC derived from fresh pig manure and fresh forest soil,and red soil is larger than brown soil under different fertilization treatments.The equilibrium adsorption of DOC on brown soil with different fertilization treatments showed a trend of NPKM>M>NPK>CK,and the red soil with different fertilization treatments showed a trend of NPKM>NPK>M>CK.The main substances adsorbed by soil to DOC from fresh pig manure are protein-like substances and soluble microbial metabolites,and the substances adsorbed by DOC from fresh forest soil are mainly protein-like substances and fulvic acid-like substances.(3)The desorption amount of DOC in the soil increased with the increase of the added concentration,and the desorption amount of red soil was greater than that of brown soil.In brown earth,compared with no fertilization treatment,the application of chemical fertilizers and organic fertilizers can significantly increase the desorption of DOC.Under different fertilization treatments,the amount of DOC desorption in red soil was: NPKM>NPK>M>CK.The desorption of DOC from fresh forest soil by soil was significantly lower than that of DOC from pig manure.The desorption substances of DOC from fresh pig manure in soil are mainly humic acid-like substances,tyrosinelike protein substances and soluble microbial metabolites.The desorption substances of DOC from fresh forest soil are mainly humic acid-like substances with different molecular weights.And fulvic acid-like substances. |
