THE EFFECT OF ORGANIC MATTER AND INORGANIC AMENDMENTS ON THE CHEMICAL KINETICS AND THE GROWTH OF RICE IN AN ACID SULFATE SOIL

Greenhouse experiments were conducted to determine the effects of straw, CaCO3, and MnO2 on the electrochemical and chemical kinetics and rice growth and yield in a flooded acid sulfate soil.Straw (0. 25% by weigh of the dry soil) application had a pronounced effect on soil reduction. High concentration of watersoluble Fe2+ stunted plants at early growth (but the Fe2+ concentration gradually decreased and plants had vig-orus growth at maturity. Grain and straw yields at harvest were higher. Potassium in the plant tissue was hight where straw was added.Adding CaCO2(0. 25% by weight of the dry soil) markedly increased soil soltuation pH,decreased Eh and EC,and significantly depressd concentrations of water-soluble Fe2+ ,Mn2+ and Al3+.Calcium carbonate,alone or in combination with MnO2,depressed Fe concentration in the soil solution and signficantly increased straw and grain yields. Calcium and MnOj applications also enhanced N and P content in the straw but decreased Zn content.Adding 0. 005% MnO2(by weight of the dry soil) increased the Mn in the soil solution,depressd the Fe:Mn ratio in the plant tissue,and increased grain yield significantly over the control. Results show that straw as an inexpensive amendment for acid sulfate soils merits further study.