Extent of soil water repellency under long-term no-till soils

Abstract

Water repellency (WR), the ability of a soil to slow the water entry (contact angle < 90°), can be indispensable to stabilize soil aggregates and promote long-term soil organic carbon (SOC) sequestration. Data on WR for agricultural soils are, however, extremely limited to ascertain the extent of this property. Thus, we assessed the WR in long-term no-till (NT) fields adjacent to plow tillage (PT) and woodlot (WL) and its statistical relationships with SOC concentration, soil particle-size distribution, and aggregate stability across 11 soils distributed in Major Land Resources Areas (MLRAs: 121, 122, and 125 in Kentucky, 99, 124, and 139A in Ohio, and 139B, 139C, 140, 147, and 148 in Pennsylvania) in the eastern US. The WR tended to increase with increasing soil water potential, and management impacts on WR depended on soil water potential. Mean water drop penetration test (WDPT) ranged from 0.5 to 12 s while water repellency index ( R index) ranged from 1.5 to 5 for air-dry aggregates in the surface 0- to 5-cm soil depth. At the same depth, WR in NT was significantly higher than in PT by 1.5 to 6.0 times in 8 out of 11 soils. These soils had weak and very weak water repellency. In MLRA 124, NT had WR 30% higher than PT soil in the 0- to 5-cm depth but had lower WR in lower depths. The SOC concentration explained 28% ( P < 0.001) of the variations in LogWDPT, which, in turn, explained 45% ( P < 0.001) of the variations in aggregate stability. The LogWDPT increased with an increase in sand concentration ( r = 0.44; P < 0.001) and decrease in clay concentration ( r = − 0.41; P < 0.001). The WDPT was moderately correlated ( r = 0.39; P < 0.05) with R index. The WDPT was more strongly correlated with SOC concentration, aggregate stability, and soil texture than R index. Overall, NT farming induced a slight increase in water repellency in most soils, attributed to increases in SOC concentration.