Effect of phosphate rocks on nutrient availability of rice on acid sulphate soils

Field trials were conducted to study on nutrient availability of four phosphate rocks (PRs) on rice growth. The trials were arranged on both reclaimed and unreclaimed acid sulphate soils from 1998 to 2001. Results indicate that all PRs could increase P content significantly in straw in the unreclaimed field, total NPK removal by grain and straw and soil P content were also increased significantly. When comparing the cumulative and residual effects (split and single P application), no significant difference between the two application methods was observed. Roots of rice take up more soil P and store in straw. On reclaimed soils, no siginificant difference was recorded. It is feasible and practical to use PRs as a substitute of available P fertilizers on acid sulphate soils. P deficiency is a crucial limiting factor for rice growth, but there are more factors than phosphorus limiting rice growth on this type of soil.