Impacts of Slope Gradient and Slope Aspect on Soil Properties of Farmland in Red Soil Hilly Region

The variation rules of soil properties in farmlands with different slope gradients and slope aspects in Nanjiang Town,Pingjiang County,Hunan Province,red soil hilly area,were studied by field sampling,laboratory analysis,statistical analysis,and the slope gradient and slope aspect were determined by digital terrain model(DTM).The results showed that the contents of soil organic matter and total nitrogen increased with increase of slope gradient,but there were no significant differences,while that in south-facing slope land was significantly higher than that in north-facing slope land in red soil hilly region;slope gradient and slope aspect had no obvious impact on soil pH value;the content of soil alkali-hydrolysable nitrogen in slope with 0~5° or 5-10° was significantly higher than that in slope with 10~15° and 15~20°,while that in north-facing slope land was higher than that in south-facing slope land;the contents of soil total phosphorus(P) and available P decreased with increase of slope gradient,that in slope with 0~5° were markedly higher than that in slope with other three gradients,while that in south-facing slope land were significantly higher than that in north-facing slope land;the soil total K content not changed with different slope gradients and slope aspects,but the soil available K content changed significantly.