The effects of gypsum-enriched slots on moisture movement and aeration in an irrigated swelling clay

Abstract

The low yields of flood irrigated row crops on transitional red-brown earths have been attributed to low infiltration rates and poor aeration. A new method for soil amelioration using gypsum-enriched slots to overcome these limitations was investigated in a field experiment. Gypsum-enriched slots were formed by excavating 0.4 m deep and 0.15 m wide parallel slots, mixing the excavated soil with gypsum and loosely refilling the slots. Moisture and aeration profiles were regularly monitored using a neutron moisture meter during the cropping season on field plots with gypsum enriched slots, and on plots with surface gypsum application and without gypsum. A sorghum crop was grown on all plots. Owing to faster flow through the slots during irrigation, the slotted plots showed deeper wetting than the no gypsum and surface gypsum treatments. Consequently the surface soil layers between the slots were subjected to less wetting and better aeration than in the other plots. The slots, which except immediately after an irrigation, showed high air-filled porosity values due to faster redistribution rates, should provide pathways for oxygen flow to the soil between slots and to lower depths. Infiltration rates measured using infiltration rings showed a twofold increase with addition of surface gypsum and a further two- to three-fold increase through the gypsum-enriched slots. The implications of the changes in the moisture and air filled porosity profiles due to slotting with gypsum for irrigated and non-irrigated cropping on these soils are briefly discussed.