奶牛放牧对人工草地土壤理化特性的影响

2004-2005年在华北农牧交错带研究奶牛不同放牧强度及放牧制度对紫花苜蓿、无芒雀麦、新麦草和蓝茎冰草混播人工草地土壤理化特性的影响，结果表明：放牧强度对人工草地土壤的物理结构影响较大，与轻度轮牧相比，中度连续放牧使土壤（0-20cm）紧实度增加19．8％，容重上升2．8％，孔隙度减少2．1％，通气性变差，含水量下降5．8％，〉0．25mm团聚体比例降低14％。放牧强度对土壤物理特性的影响随土层深度增加而显著减小，土壤pH值、全氮、速效氮和速效钾含量增加，而速效磷含量降低。

Effects of Dairy Cows Grazing on Soil Physical and Chemical Properties of Alfalfa-grass Pasture in Agro-pastorai Transitional Zone of North China

The effects of grazing dairy cows on physical and chemical characteristics of soil of the swards of Alfalfa-grass were studied from 2004 to 2005 at Guyuan Grassland Research Station of China Agriculture University in Hebei province.The result showed that grazing intensity directly influenced the physical structure of soil for the swards.The soil bulk density increased along with the increment of grazing intensity,while water content and porosity were decreased both for 0~10 and 10~30cm layer.The impact of grazing intensity on soil physical characteristics decreased with the increment of soil depth.The increment of soil bulk density,compaction,total porosity,water content and proportion of >0.25mm soil aggregates in the 0~20cm layer were 2.8%,19.8%,-2.1%,-5.8% and 14% respectively in moderate continuous grazing compared with light rotational grazing.The content of available phosphorus in the soil decreased with the increment of grazing intensity at 2.5%,while the contents of pH,gross nitrogen and available potassium in the soil increased with the increment of grazing intensity at 0.5%,9%,13% and 7.6%,respectively.