Abstract: This paper focused on the changes of chemical composition of shallow groundwater in the process of agricultural land use and its the effect on the quality of shallow groundwater by investing the soils and sampling groundwater and runoff in karst rocky desertification areas of Guizhou province. The results showed that under the order of ecological pattern from forest ecological system, forest-agriculture ecological system, dry farming ecological system to complex agriculture ecological system, the contents of HCO3−, SO42−, Ca2+, Mg2+ , Na+, K+, NO3−, Cl−, NH4+, PO43−, Pb in the groundwater of karst rocky desertification areas were significantly taken place to change, which the contents of NH4+, Pb, Cd were obviously increased in the regions with lower index of planting crops and the contents of SO42− , NO3−, NH4+, Pb, Cd , Cr were丂significantly enhanced in the regions with higher index of planting crops so to impact on the quality of groundwater. In the process of agricultural land use, the mainly factors of impacting on the quality of groundwater were the structures of planting crops and fertilizing level in those areas, which with increasing of planting crop index and fertilizing levels, the quantities of NO3−, PO43− from agricultural soil to water body were obviously enhanced so to potentially effect on the quality of groundwater. Thus, developing agricultural productions must pay attention to protect groundwater resource in karst areas.

Key words: Karst, Rocky desertification, Agricultural land use, Shallow groundwater, Water quality