Effective Land and Water Management for Controlling Solutes from Acid Sulfate Soils in Mekong Delta Paddy Fields

抄録

Actual acid sulfate soils have emerged across large areas of the Mekong Delta due to oxidation of potential acid sulfate soils following land reclamation for mainly agricultural use. Despite adverse conditions for crop production, due to strong acidity and high salinity, suitable water management and chemical fertilizer application enables rice to be grown on agricultural land of actual acid sulfate soils. Changes in the water properties of canals in the double cropping system of a paddy field in areas of actual acid sulfate soils were monitored to evaluate the effect of water management and fertilizer application upon water quality. Canal water adjacent to the paddy field was periodically collected, and general chemical properties were analyzed. The great variation in pH (2.8–6.3) and electric conductivity (EC; 0.1–1.5 dS m^-1) in the drained water seemed to be closely associated with water management of adjacent paddy fields. Canal water collected in the growing season had a low pH and high EC, while a neutral pH and low EC were observed in the fallow season. Values of EC and pH correlated with major components of solutes such as SO₄, Ca, Mg, and Al ions. Al concentration in the acidic water was extremely high, peaking at 260 mg L^-1 in the rice crop season. Inundation and drainage for rice cropping is a major controlling factor for the release of solutes from the soil into drained water. It is important therefore to determine the time lag between initiation of soil management and the consequent changes in the surrounding water system.