放牧对降雨条件下黄土高原退耕草地土壤水分补给的影响

Effects of grazing on soil water recharge of rehabilitated grassland under natural rainfall on the Loess Plateau,Northwest China

降雨是影响土壤水分补给和坡面产流的关键因素,放牧可改变地表覆被特征和表层土壤结构,进而影响坡面产流和土壤水分补给。目前鲜有研究关注放牧对土壤水分补给的影响。本研究通过围栏放牧试验,定位监测自然降雨条件下土壤水分动态,对比了不同放牧强度(G1~G5:2.2、3.0、4.2、6.7、16.7羊·hm^(-2))下地表覆被、土壤理化属性和降雨土壤水分补给特征。结果表明:放牧显著影响植被和生物结皮盖度,与不放牧样地(NG)相比,G1~G5放牧强度下植被盖度降低8.3%~16.4%,G2放牧强度下生物结皮盖度较NG增加106.9%。G1~G5放牧强度下地表粗糙度增加53.1%~152.5%,G5放牧强度下生物结皮厚度降低24.1%。土壤湿润锋速随降雨强度增加而降低,G2放牧强度下0~5 cm土层湿润锋速在不同降雨条件下(降雨量18.0~70.3 mm)与NG相比降低60.0%~83.3%。放牧对土壤湿润锋速的影响与生物结皮盖度和0~5 cm土壤容重显著相关。放牧未显著影响黄土高原降雨条件下土壤水分补给速率。综上,G2放牧可通过增加藻结皮盖度,延长土壤水分在表层土壤的运移时间,有益于干扰后表层土壤微生态环境恢复。本研究结果可为“后退耕时代”黄土高原退耕草地水分管理提供科学依据。

Rainfall is critical to the regulation of slope runoff and soil water recharge.Grazing affects land cover and soil structure,with consequence on slope runoff generation and soil water recharge.Little attention has been paid to the effects of rainfall on soil water recharge caused by grazing.In this study,we examined land covers and soil water contents under different grazing intensities(G1-G5:2.2,3.0,4.2,6.7,16.7 sheep·hm^(-2))and no grazing sites(NG),aiming to analyze soil water recharge under natural rainfall conditions after grazing.The results showed that grazing exerted significant effects on vegetation and biocrust coverage.The vegetation coverage was decreased by 8.3%-16.4%under G1-G5 grazing,while the biocrust coverage was increased by 106.9%under G2 grazing compared to NG.The soil surface roughness under G1-G5 grazing was increased by 53.1%-152.5%,and the thickness of biocrust was decreased by 24.1%under G5.Soil wetting front velocity decreased with increasing rainfall intensity,and that of 0-5 cm layer under the G2 grazing intensity decreased by 60.0%to 83.3%under rainfall between 18.0 mm and 70.3 mm compared to NG.The effect of grazing on soil wetting front velocity was significantly related to biocrust coverage and soil bulk density of 0-5 cm soil layer.Generally,grazing did not affect soil water recharge rates of the slope grassland on the Loess Plateau.G2 grazing may prolong the migration time of soil water in the surface layer by increasing the coverage of cyanobacteria biocrusts,which may be beneficial to the restoration of soil microenvironment.Our results provided scientific basis for water management in the enclosure grassland of the Loess Plateau in the“post-conversion era”.