Spatial Distribution of Water Repellency of Soils on Plots Planted with Different Crops in Karst Regions

Spatial distribution of water repellency of the soils from plots planted with different crops was studied under the dry, moderately or wet soil conditions. Soybeans, sugarcane or pear trees were grown on the plots in the karst region near Guilin Institute of Agricultural Sciences in Guangxi. The spatial distribution of water repellency in the soils from the plots was determined by using a geostatistical analysis on the plots of 135 m×105 m in size. There were 100 sampling points on each plot for measurement of water drop penetration time (WDPT). The soils were also classified according to their moisture content as dry (0.062±0.025) cm³·cm^-3, moderately (0.151±0.045) cm³·cm^-3 or wet (0.237±0.086) cm³·cm^-3. The results showed that, under dry and wet conditions, the greatest WDPT and contents of moisture and organic matters were found in the soil where pear trees were grown, while the lowest on the soybean plot. However, under the moderately wet soil condition, the lowest values on these parameters were on the sugarcane plot. Meanwhile, the water retention time reached a maximum for all plots. It appeared that geostatiatical analysis significant correlation existed among the spatial distribution of water repellencies in 3 planting plots under 3 soil conditions as the ratio was substantially greater than 75%.Due to the high threshold water repellency distribution, the soil at the sugarcane plot seemed to be more stable than that at the soybean field, while that at the pear tree plot being the weakest of all. It suggested that the soils might be able to recover spatial distribution of water repellency after being disturbed by human activity.