Reducing iron toxicity in rice with resistant genotype and ridge planting
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Iron toxicity reduces rice (Otyza sativa L.) grain yield in many poorly drained swamps in West Africa. Two methods for alleviating Fe toxicity were examined, (i) the use of a resistant genotype, and l(ii) planting on ridges to aerate the upper root zone. Grain yield responses to these factors were measured in field trials conducted .in an inland valley swamp in southeastern Nigeria over two seasons on a set of paddies ranging from nontoxic to severely toxic. Two genotypes were compared, ITA 212 (susceptible) and ITA 247 (resistant). The severity of Fe toxicity in each paddy was estimated by visually scoring symptoms on ITA 212. Yield decline with increasing toxicity score fit simple linear regressions for both genotypes, but slopes differed significantly. On nontoxic paddies, ITA 212 yielded :10% more than ITA 247, but ITA 247 yielded 10 to 250% more than ITA 212 as toxicity increased from moderate to severe. Ridge planting did not significantly affect grain yield in 1985, but increased it by 245% in 1986 on a severely toxic paddy. The large increase in 1986 was attributed to the use of higher ridges (120 mm above the water surface) than in 1985 (30 mm). In both years the response to ridging was significantly greater when the resistant genotype was used. Resistant genotype and ridging appear to be effective technologies for reducing yield losses on Fe toxic soils, especially when used in combination.