The effect of different levels of soil water repellency resulting from the addition of manure on soil stability and soil water availability characteristics

Soil water repellency is an important physical phenomenon. In sub-critical water repellency conditions, many studies have reported positive repellency impacts. It seems that the presence of soil water repellency in a Specified range (Optimum water repellency) is not only a cause of destructive impacts in the soil but also is a positive factor in improving the soil physical quality. In this study, pre-treatment of organic matter (as a hydrophobic agent) was applied on 0, 1, 3, 5, 8 and 10% by weight of manure, on sandy loam and clay loam samples (In Kerman province; through 2020-2021). After three months incubation period and wetting and drying cycles of soils, soil water repellency was calculated using WDPT (Water drop penetration time), RI (Repellency index) and β methods. Then 21 soil quality indices (water availability and soil stability structure characteristics) were measured in the samples, and MDS (Minimum data set) indicator were selected using PCA (Principal component analysis). The Optimum water repellency, which is equal to 0.95 of the predicted values with the equation fitted to data, was calculated by plotting the data of MDS indicator and water repellency index. Considering the significant effect of manure on soil water repellency indices, and also the significant correlation of RI with most of the water availability and soil structure characteristics, RI was selected to determine the optimum water repellency. After checking the results of graph and 11 MDS indictors, it was determined that DC, TS and Ql indictors had a decreasing and then increasing trend with increasing water repellency, and the rest of indictors showed an increasing trend and then a decreasing trend. The Range of Optimum water repellency (0.95LL-0.95UL) is defined in an extensive range (4.40-4.86), when the soil structure indictors are investigated and in a limited range (3.72-4.28) when it is only affected by water availability. Finally, in unlimited conditions, the lower limit of 3.72 and the upper limit of 4.28 were considered for the optimum water repellency.