Factors Affecting Rice Growth on Acid Sulfate Soils

Abstract

AbstractRice (Oryza sativa L.) yields on acid sulfate soils, which comprise a sizable portion of the rice‐growing area in Southeast Asia, are constrained by soil parameters. The objective of this study was to identify those parameters most strongly related to rice growth. Metal availability and uptake by rice were evaluated in the Central Plains of Thailand using 134 flooded acid sulfate soils and in a growth chamber utilizing 50 of them. Nutrient‐uptake data indicated that uptake of divalent cations was most closely correlated to the divalent activity ratio (Ametal). Although many individual parameters were correlated with rice growth, results from multiple correlation analysis indicated that AFe (the ratio of Fe2+ activity to the sum of the activities of all other divalent cations), pH, and ionic strength provided the best three‐variable model describing dry‐matter production in the growth‐chamber study. In the field, the best two‐variable model describing yields included pH and AFe. Therefore, the most important constraints to rice growth on acid sulfate soils were (i) acidity, which includes the combined effects of pH, Al toxicity, and P deficiency, and (ii) Fe stress, which is due to the combined effects of Fe toxicity and deficiencies of other divalent cations such as Ca. This study indicates the importance of divalent activity ratios such as AFe when studying metal uptake or modeling plant growth. In a micronutrient fertility trial conducted under greenhouse conditions, the only significant yield response occurred when Si was applied to a limed acid sulfate soil.