农牧交错带草地开垦对土壤有效态微量元素的影响及评价

为明确草地利用方式转变对土壤微量元素的影响,以华北农牧交错带2种类型草地及其相应开垦的农田为对象,采用成对设计的方法研究了开垦对草地土壤表层(0～20cm)有效态微量元素(铜、铁、锰、锌、硼、钼)的影响并对其进行了评价,以期为农牧交错带的科学管理提供参考。结果表明:典型草地开垦导致土壤有效态铜、锌含量分别上升8.8%和16.4%,其他4种微量元素含量下降16.4%～28.1%。根据土壤有效态微量元素评价标准,典型草地区域有效态硼、钼含量处于高水平,有效态铜处于中等水平,有效态锌处于极低水平;有效态铁、锰在典型草地为高水平和中等水平,开垦为农田后分别降到中等水平和低水平。低湿草甸开垦导致微量元素含量下降10.6%～77.7%,其中有效态铁、硼、钼处于极高水平,有效态锰处于中等水平,有效态锌处于极低水平;有效态铜由低湿草甸的高水平降到农田的中等水平。整个研究区土壤有效锌含量限制草地植被和农作物生长发育,由典型草地开垦的农田其土壤有效锰含量不能够满足作物的需求。建议研究区禁止开垦草地并对已开垦的草地实行退耕还草,同时建议建立基于土壤微量元素密度的评价体系。

Effect and evaluation of soil trace elements after grassland converted into cropland in agro-pasturage ecotone of northern China

The soil available trace elements are very important to plant growing. The paired-site design was used to explore the effect of different grassland use on soil trace elements and evaluate the contents of soil trace elements, which would be helpful to develop scientific strategies for land use in the agro-pasturage ecotone of northern China. In the present study, the contents of soil available trace elements (Cu, Fe, Mn, Zn, B, Mo) were measured in typical grassland, meadow and their counterpart croplands. The results showed that the soil available Cu, Zn contents increased by 8.8% and 16.4% respectively after typical grassland converted into cropland; Soil available Fe, Mn, B and Mo contents decreased by 16.1% to 28.1%. According to soil available trace elements evaluation criteria, the soil available B and Mo were at high level, and Cu at medium level, Zn at extremely low level in both typical grassland and counterpart croplands. The soil available Fe and Mn decreased from high and medium levels to medium and low levels after typical grassland converted into cropland. The meadow reclamation made six soil available trace elements contents decrease by about 10.6%-77.7%, where the available Fe, B, and Mo were at extremely high level, and Mn at medium level, Zn at extremely low level in meadow and counterpart croplands. Soil available Cu decreased from high level to medium level after meadow converted into cropland. The soil trace elements below medium level could not meet the demands of grass vegetation and crop growing. It was suggested that the farmers should reserve high crop residue in the farmland and improve soil quality by returning straw to field and applying trace element fertilizer. Meanwhile it would be an importance to stop reclaiming the typical grassland, to return the crop field into grassland and scientifically use the meadow in agro-pastoral ecotone of northern China. It is suggested that the new evaluation criteria of soil trace element based on soil trace element density should be built.