SURFACE-WATER MANAGEMENT UNDER VARYING DRAINAGE CONDITIONS FOR RICE ON AN ACID SULFATE SOIL IN THE MEKONG DELTA, VIETNAM

In the period 1990-1992, three field experiments were carried out to e valuate the effects of (repeated) removal of surface water under varyi ng drainage conditions, with the aim of alleviating suspected Fe toxic ity aggravated by H2S together with Al toxicity. The experiments were carried out on a poorly drained, heavy textured, acid sulphate soil (t ypic Sulfaquept) of low permeability. The results of the experiments i ndicate that surface water management can alleviate nutritional disord ers and increase yield. These effects are, however, overruled by the i nfluence of the general drainage condition of the land. Evaluation of agronomic and soil chemical parameters indicates that in the Hoa An co nditions a percolation rate of 0.8-1.0 mmday(-1) appears to be optimal to prevent most adverse soil conditions. A set of practical soil- and water-management measures is presented which can be used to improve t he yield under similar hydrological and soil conditions. (C) 1997 Else vier Science B.V.