The ferrous requirement of rice is greater than that of other plants. Ferrous sulfate deficiency is a common disorder of rice growing on well-drained (aerobic) soils, whether these are neutral, calcareous or alkaline. The severity of the disorder increases with the pH. Ferrous deficiency may also be observed in rice on upland acid soils.
In flooded rice paddies, ferrous deficiency is likely to be found in calcareous and alkaline soils low in organic matter, and in soils irrigated with alkaline water.Ferrous deficiency may also be a problem in peat soils, especially if these are well-drained, and with a high pH.
Diagnosis by Soil Analysis
Well-drained soils with a pH of more than 6.5 are likely to be deficient in available ferrous. The severity of the problem increases with a high pH.
In flooded rice soils, ferrous deficiency may occur if the redox potential of the soil at a pH of 7 is more than 0.2 volt. In this situation, the total soil ferrous content may be high, but the level of availabale ferrous in the soil remains low.
Interaction with Other Elements
A high concentration of calcium carbonate in the soil or irrigation water is likely to make ferrous deficiency of rice more severe. Ferrous deficiency can sometimes be caused by too much nitrate, which raises the pH of the soil around the roots. High phosphate applications may cause ferrous deficiency, or make it worse, by precipitating ferrous in the soil solution. High phosphate levels may also hinder the uptake of ferrous by plants, and the translocation of ferrous from the root system to the shoots.
How to Correct Ferrous Deficiency in Rice
Ferrous deficiency can be amended by applying a foliar spray of 2-3% ferrous sulfate solution. Another way of correcting the deficiency is to apply about 30 kg/ha of ferrous sulfate to the soil. Because of the low mobility of ferrous sulfate in the plant, split applications may be necessary.