Amelioration of iron deficiency in rice and transformations of soil iron in coarse textured soils of Punjab, India

Abstract

The productivity of coarse textured soils is generally low due to their poor inherent fertility in particular due to the low water holding capacity and nutrient availability. With the adoption of irrigated upland rice‐wheat cropping system on these soils where water cannot be impounded even after puddling, widespread deficiency of Fe has been reported in rice. Iron deficiency is most severe when the coarse textured soils are brought under rice cultivation for the first time. Iron deficiency in rice grown on such soils results from inherent low Fe content of soils and unfavorable conditions for reduction of Fe³⁺ to Fe²⁺. In field experiments, soil application of even 200 kg FeSO₄7H₂O ha⁻¹ proved inferior compared with 3‐sprays of 1% FeSO₄7H₂O solution for remediation of Fe deficiency in rice. Incorporation of Sesbania aculeata green manure before transplanting rice was very effective in ameliorating Fe deficiency and significantly increasing rice yield and DTPA‐extractable Fe in soils. Results of greenhouse experiments demonstrated that incorporation of Sesbania green manure markedly decreased pH and redox potential (Eh) and increased ionic strength, partial pressure of CO₂ and Fe concentration in soil solution. Chemical equilibria studies showed that Fe solubility was controlled by Fe(OH)3‐Fe²⁺ system throughout the periods of submergence and after the peak of Fe²⁺ in the soil solution Fe₃(OH)8‐Fe²⁺ and Fe(OH)3‐Fe3(OH)s systems were predominant. Under field conditions transformations of a part of Fe from the crystal lattice and/or cristalline oxides of Fe to amorphous oxides and bound by carbonates over the years increased the availability of Fe in the soils.

Notes

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