室内模拟水分管理对土壤溶液磷质量浓度影响研究

The Effects of Soil Water Content on Distribution of Mobile Phosphorus Concentration in Soil

【目的】探究不同水分管理模式下、不同土层土壤溶液磷的环境行为。【方法】本研究采取土柱试验研究了3种水分管理模式下(模式1—模式3土壤含水率均恒定分别为:50%、75%、100%)84 d剖面土壤(表层0~10 cm、中层10~20 cm、下层20~30 cm)溶液磷质量浓度变化规律及其与土壤溶液中TOC、总铁、总铝、总钙之间关系。【结果】水分管理对土壤溶液磷质量浓度有显著的影响,并与土层有关;表层土壤表现为:模式3(1.27 mg/L)>模式2(0.82 mg/L);中层土壤表现为:模式3(1.60 mg/L)>模式2(1.40 mg/L);下层土壤表现为:模式3(0.31 mg/L)>模式2(0.17 mg/L)>模式1(0.13 mg/L)。逐步回归分析揭示土壤溶液总磷质量浓度与土壤溶液TOC、总铁、总铝、总钙有关,并受水分管理模式和土壤层深度的影响。室内模拟3种水分管理模式下土壤溶液总磷质量浓度都大于地表水富营养化标准值(0.1 mg/L)。【结论】退耕还湿期间土壤磷释放可能会引起上覆水磷质量浓度突然升高,其造成的生态环境问题值得关注。

【Background and objective】Concentration of mobile phosphorus(P)in soil affects not only plant growth but also water quality because of its potential leaching.Most studies on soil P focused on topsoil while overlooking subsoil which is equally important.The objective of this paper is to study the dynamics of mobile P at different soil depths and its driving forces in attempts to help improve P uptake by plants while in the meantime reducing its leaching.【Method】Column experiments filled with soil taken from Sanjiang plain in China were conducted with average volumetric soil water content controlled at 50%(M1),75%(M2)and 100%(M3)respectively.In each treatment,we measured the changes in mobile phosphorus in the depths of 0~10 cm(topsoil)10~20 cm(middle soil)and 20~30 cm(subsoil).We also analyzed its relationship with total organic carbon(TOC),total Fe,total Al and total Ca in soil solution;the experiments lasted 84 days.【Result】When soil water content was 50%,soil solution was not extractable from the topsoil and the middle soil,and only was limited water extracted from the subsoil.When soil water content exceeded 75%,soil solution was more mobile for extraction in which the P concentration in the middle soil was found to be the highest,1.3~1.7 times that in the topsoil and 5.2~8.2 times that in the subsoil.The impact of soil water on P concentration varied with soil depth and was ranked in the following order:In the topsoil,M3(1.27 mg/L)>M2(0.82 mg/L),in the middle soil M3(1.60 mg/L)>M2(1.40 mg/L),and in the subsoil M3(0.31 mg/L)>M2(0.17 mg/L)>M1(0.13 mg/L).A stepwise regression analysis indicated that P concentration in the soil solution was related to TOC,total Fe,total Al,and total Ca in soil solution,with the correlations varying with soil water and soil depth.These suggested that improving soil water management could shift dissolution and/or decomposition of P in different forms in the soil,and can thus bed used to manage soil P.Regardless of soil water content,P concentration in the soil was much higher than the critical P concentration,0.1 mg/L,which could trigger eutrophication in surface water.【Conclusion】Increasing soil water could result in a quick release of P from soil to the overlying surface water,triggering eutrophication as a result.Care thus must be taken when temporally returning dry farmland to wetland.