Development of Seasonal Water Repellence under Direct Drilling

Water repellence was detected in an Oxic Paleustalf medium‐textured surface soil (27% clay,) under direct drilling but not under conventional cultivation. The phenomenon was apparently seasonal in nature, evident after the first rain in summer but disappearing after a period of relatively high rainfall. Water repellence was reproduced in the laboratory by slow drying soil cores under high relative humidity and was associated with fungal hyphae growing on the organic‐matter‐rich surface layer developed under direct drilling. Either rapid drying or wetting of the soil with a dilute thymol [5‐methyl‐2‐(1‐methylethyl) phenol] solution instead of water stopped the fungal growth and development of water repellence. Water repellence significantly slowed infiltration when water was applied at 40‐mm suction using a sorptivity tube. The seasonally developed water repellence found in the direct‐drilled soil was probably the result of enhanced fungal growth due to the absence of soil disturbance and presence of a permanent layer of organic matter.