AMELIORATION OF A HARDSETTING ALFISOL THROUGH DEEP MOLDBOARD PLOWING,GYPSUM APPLICATION AND DOUBLE CROPPING .2. SOIL-WATER RELATIONS

Deep mouldboard ploughing to a depth of 0.45 m, gypsum (5 t ha-1) and double cropping wheat (Triticum aestivum) with a summer forage crop we re applied individually, and in combination, to modify a hardsetting r ed-brown earth (Alfisol) used for flood-irrigated wheat production. Th e effects of these treatments upon water infiltration, storage and int ake during irrigations, application efficiency, and depletion between irrigations were measured. Gypsum markedly increased saturated hydraul ic conductivity (K(S)) immediately after being applied in June 1984 bu t not in 1985. Mouldboard ploughing and double cropping had little eff ect on K(S). All K(S) values were less than 0.5 m day-1. Plant availab le water content (PAWC) was increased by gypsum application and mouldb oard ploughing after the initial irrigation in 1984, and by the three main treatments in 1985. The order in which the main treatments increa sed PAWC was: gypsum > mouldboard ploughing > double cropping. Water a pplied and water intake during irrigations were increased by mouldboar d ploughing and gypsum during the first irrigation in 1984 by as much as 60 mm. Thereafter mouldboard ploughing, gypsum and double cropping had little effect on water intake, and only gypsum increased the amoun t of water applied in 1985. The ratio of water intake to water applied during irrigations (application efficiency) was increased by mouldboa rd ploughing to 59% in 1984; no treatment had values greater than 40% during 1985. Water depletion was significantly increased by mouldboard ploughing in 1984 and by gypsum and double cropping in 1985. Few sign ificant interactions were found between the three main treatments, eac h of which would improve soil-water relations for crop growth, althoug h the effect of mouldboard ploughing on soil-water relations declined after the first year. Despite substantial improvements after 2 years i n some treatments, soil hydraulic properties were inadequate for optim al irrigated cropping.