Iron Toxicity in Lowland Rice

ABSTRACT

Lowland rice is a staple food for more than 50% world population. Iron toxicity is one of the main nutritional disorders, which limits yield of lowland rice in various parts of the world. The toxicity of iron is associated with reduced soil condition of submerged or flooded soils, which increases concentration and uptake of iron (Fe^{2 +}). Higher concentration of Fe^{2 +} in the rhizosphere also has antagonistic effects on the uptake of many essential nutrients and consequently yields reduction. In addition to reduced condition, increase in concentration of Fe^{2 +} in submerged soils of lowland rice is associated with iron content of parent material, oxidation-reduction potential, soil pH, ionic concentration, fertility level, and lowland rice genotypes. Oxidation-reduction potential of highly reduced soil is in the range of –100 to –300 mV. Iron toxicity has been observed in flooded soils with a pH below 5.8 when aerobic and pH below 6.5 when anaerobic. Visual toxicity symptoms on plants, soil and plant tissue test are major diagnostic techniques for identifying iron toxicity. Appropriate management practices like liming acid soils, improving soil fertility, soil drainage at certain growth stage of crop, use of manganese as antagonistic element in the uptake of Fe^{2 +} and planting Fe^{2 +} resistant rice cultivars can reduce problem of iron toxicity.

Keywords:

• DTPA iron extracting solution
• Oryza sativa L.
• oxidation-reduction potential
• reduction processes
• submerged soils

Notes

¹Soil samples were analyzed from the States of Goiás, Mato Grosso, Mato Grosso do Sul, Paraná, Minas Gerais, Rio Grande do Norte, Piauí and Maranhão.

∗∗ Significant at the 1% probability level.

∗,

∗∗Significant at the 5 and 1% probability level, respectively.