Effects of gypsum‐slotting on infiltration rates and moisture storage in a swelling clay soil

Previous studies have shown marked increases in wheat yields on a swelling clay soil due to gypsumslotting compared to no‐gypsum and surface gypsum applications, largely through improved aeration in the surface layers. In the present study, steady infiltration rates indicated 2‐fold increases due to surface gypsum applications and 4‐ to 6‐fold increases due to slotted gypsum. This should provide increased moisture storage and reduced soil erosion hazards during prolonged heavy rainfall periods, provided that a crust does not form under the impact of raindrops. However, gypsum‐slotted lands should not be used in crop rotations which include ponded rice, due to increased potential water use and risk of rising watertables and salinization. The effect of the ‘throttle’ in the upper B horizon which restricts moisture storage in the lower soil layers during short‐term and prolonged ponding was reduced, but not eliminated, by surface and slotted gypsum applications. Thus the moisture contents of the lower depths in both the non‐ameliorated and ameliorated soils were less than the moisture content at saturation or at ‐10 kPa potential even after flooding for 11 days.