Soil and Water Sciences Division, International Rice Research Institute, P.O. Box 933, 1099, Manila, Philippines.
1Present address: Soil-Water-Plant Relationship Laboratory, Water Technology Centre for Eastern Region, Chandrasekharpur, Bhubaneswar, 751023.
Greenhouse experiment was conducted to study iron (Fe) and potassium (K) availability to rice (Oryza sativa L. cv. IR43) in two soils - a near-neutral Tropudalf and a strongly acidic Sulfaquept - under three water regimes, viz. moist, wet and flooded conditions. While soil reduction brought on by flooding had little effect on the solubility of K, it markedly increased Fe solubility in both the soils. Concentration of water-soluble Fe in the acid sulphate soil reached as high as 377 mg L−1 within the first 4 weeks after flooding, while maximum concentration of Fe in the near-neutral soil was 40 mg L−1 attained 8 week after flooding. Growth and yield of rice plants were adversely affected by iron toxicity in the flooded acid-sulphate soil. Potassium and Fe analyses in plants at maximum tillering as well as at maturity suggested that the occurrence of Fe toxicity in wetland rice was associated with low K to Fe ratio in the tissue. Potassium to Fe ratios in the most healthy and iron-toxic rice plants were found to be 53 and 12, respectively, at maturity; and 245 and 38, respectively, at the maximum tillering stage.
Acid-sulphate soil, water regime, K and Fe solubility, rice, iron toxicity
