Effects Of Organic Manure And Its Dissolved Organic Matter On The Transport And Transformation Of Pb In Soil

Livestock and poultry breeding industry is developing rapidly in China,and the conversion of abundant livestock and poultry manure into organic fertilizer is the best embodiment of resource utilization,which is significant to waste utilization and ecological optimization.Organic fertilizer prepared from livestock and poultry can improve soil fertility and increase crop yield.However,the application of organic manure with low maturity may cause environmental problems in soil,such as heavy metal pollution.Because organic manure contains a large amount and high activity of dissolved organic matter（DOM）,they can change the activate heavy metals（even those that have been stabilized in the soil）,and cause their migration in soil,which will increase the absorption of heavy metals by crops and ultimately endanger human health.Therefore,in this study,farm chicken manure organic fertilizer,commercial chicken manure organic fertilizer and their DOM were used as test materials,acid black soil and red soil were used as test soil,and Pb was used as target pollutant.Soil cultivation,adsorption,migration and leaching were employed to investigate the effects of chicken manure organic fertilizer and DOM with different maturity on the migration and transformation of heavy metals in soil,which will provide theoretical basis for the safe utilization of organic fertilizer.The main results are as follows:（1）The soil fertility of black soil used in this study was better than that of red soil,and the content of heavy metals in red soil was higher than that of black soil.The organic fertilizer from farm chicken manure smelt bad,and the extracted DOM was dark in color,bad in taste,high in total organic carbon（TOC）and rich in protein compounds.However,commercial chicken manure organic fertilizer had no peculiar smell,and the extracted DOM was light in color,low in TOC and rich in humic acid and fulvic acid content.The contents of heavy metals in both organic fertilizers were low.Overall,the maturity of farm chicken manure organic fertilizer was obviously inadequate.（2）Different organic fertilizers,DOM and soil types have important effects on the proportion of Pb in soil.Compared with no fertilization,the application of farm chicken manure organic fertilizer（FCM）increased soil p H by 1.18-1.63 units,increased the proportion of residual Pb by11.24-23.21%,and kept the proportion of weak acid extracted Pb at a minimum of 2.6%.The application of commercial chicken manure organic fertilizer（CCM）increased the soil p H by 0.35-0.79 units,increased the residual content of Pb by 8.75-19.02%,and increased the weak acid extracted content of Pb by 0.21-9.21%The addition of farm manure DOM（FCMD）reduced the residual content of Pb in soil by 16.3-27.52%,and increased the weak acid extracted content of Pb the residual content of Pb in soil by 6.66-13.98%.And the potential action sequence of organic fertilizer DOM on Pb migration and activation in black soil was FCMD>CCMD>CK>CCM>FCM,the order of action on low pollution concentration red soil was FCMD>CCMD>CK>CCM>FCM,and the order of action on red soil with high pollution concentration was FCMD>CCMD>FCM>CK>CCM.Generally speaking,FCM and CCM had passivation effect on Pb,while FCMD and CCMD had obvious activation effect on Pb.（3）The adsorption amount of Pb²⁺in soil was significantly reduced by FCMD.FCM and FCMD were involved in the process of adsorption of Pb²⁺in black soil and red soil.After adsorption equilibrium,the p H and electrical conductivity（EC）of FCM treatment group were 1.32-1.61 units and 735.7-748.3μs/cm higher than those of FCMD,respectively.Fourier transform infrared analysis showed that FCM was mainly composed of carbohydrates,while the content of aromatic unsaturated functional groups and other active functional groups of FCMD was high.The adsorption amount of Pb²⁺in soil with MD was obviously lower than that in FCMD group,and the adsorption amount of Pb²⁺in black soil was higher than that in red soil.（4）The application of FCMD could obviously change the physicochemical properties of black soil and red soil,and promote the migration and dissolution of heavy metal Pb.When the concentration of Pb²⁺in the influent was 300 mg/L,the complexation ability between FCMD and Pb²⁺was weak,and the acidic environment of soil could promote the leaching of FCMD.The concentration of Pb²⁺in the effluent of black soil and red loam column was 1.39 times and 0.22times higher than that in the influent,respectively,which indicated that FCMD would cause the original Pb²⁺in the soil to be dissolved and released into the effluent.FCMD obviously promoted the release of Pb²⁺in Pb-polluted black soil and red soil,and increased the leaching amount of Pb²⁺in Pb-polluted black soil and red soil by 0.82-6.73 times and 3.08-3.91 times,respectively,which indicated that FCMD could indeed activate Pb in soil and the stable Pb was transformed into a more active state.The dissolution and release of Pb²⁺from Pb-contaminated soil by FCMD was also related to soil types,and the activation of black soil was stronger than that of red soil.To sum up,farm chicken manure organic fertilizer with insufficient maturity could passivate Pb,but it could’t promote Pb migration,and its effect was obvious only in black soil with high organic matter content and strong self-purification ability.However,when the pollution concentration of Pb in red soil with poor self-purification ability exceeds 300 mg/kg,farm chicken manure organic fertilizer hardly passivated Pb,and even the stable Pb would be activated.In addition,DOM of farm chicken manure organic fertilizer can significantly activate Pb.Therefore,in the planting areas polluted by Pb,especially in the soil with high Pb content,livestock manure and livestock manure organic fertilizer with insufficient maturity should be carefully applied.