Soil and crop management technologies for enhancing rice production under micronutrient constraints

Micronutrient deficiency is considered as one of the major causes of the declining productivity trends observed in ricegrowing countries. The submergence created for rice cultivation influences electrochemical and biochemical reactions, and alters pH, pCO2 and the concentration of certain ions. This environment increases the availability of Fe and Mn with concomitant decrease in Zn and Cu. It is well known that Zn deficiency is predominant in lowland ecosystems. Sodic and upland soils and calcareous coarse-textured soils with low organic matter content suffer from Fe deficiency, besides Zn and Cu deficiencies. Rice cultivars do not experience deficiency of B and Mo. The acid soils and the lowlying, poorly drained alluvial and colluvial soils are prone to Fe toxicity. Experiments in different agroecological zones all over India showed that Zn doses to correct Zn deficiency varied from 2.5 to 22 kg ha-1; 5.3 kg Zn ha-1 proved optimum and economical, with a maximum rice yield increase of 4.8 t ha-1. In the lowland ecosystem, amending the soil with the required amount of Zn before transplanting was effective and easy to adopt, compared with repeated foliar sprays of 0.5% ZnSO4 or use of Zn-enriched seedlings through seed soaking in 2–4% ZnSO4 solution, fertilizing the nursery with Zn, or seedling root dipping in 2% ZnO slurry. Hepta as well as monohydrated ZnSO4 were better than other sources of Zn (ZnO, ZnCl2 and Zn frits). The Zn-blended diammonium phosphate (Zn-DAP), superphosphate, and nitrophosphates also proved effective. The Zn-enriched organic manures (farmyard manure, green leaf manure, and coir pith compost) were found advantageous for the direct and residual crops. Zinc fertilization with an optimal dose of 25 kg ZnSO4 ha-1 once a year yielded high economic return. A differential response of rice up to a maximum increase in yield of 4.8 t ha-1 was observed with the foliar spray (1–2% FeSO4 solution) or soil incorporation of Fe (50 kg FeSO4 ha-1) with bulky organic manure (12.5 t ha-1). The application of 12.5 kg CuSO4 ha-1 ameliorated Cu deficiency and significantly enhanced rice production. Management strategies such as liming and additional multinutrient supply (P. K, Mg, Zn, Cu, and B), besides improving drainage, enhanced the rice productivity of soils prone to Fe toxicity by correcting the multinutrient deficiency syndrome.