Management of Micronutrients in Soil for the Nutritional Security

Availability of soil micronutrient is a major limiting factor in crop productivity and its quality. The micronutrient deficiencies of zinc (Zn) 40%, iron (Fe) 12.6%, copper (Cu) 4.5%, manganese (Mn) 6.0%, and boron (B) 22.8% in soils have been reported across the country. The manganese deficiency is emerging extremely fast, particularly in wheat crops grown after rice in Haryana (12%) and Punjab (18%) due to leaching of Mn from the upper surface of the coarse-textured soils. In acid soils of India, the majority of the soil samples indicated a sufficient supply of Cu, Fe, and Mn, low deficiencies of Zn (30%), and higher deficiencies of B (46%) and Mo (50%). Application of soil or foliar spray of Zn, Mo, and B and foliar spray of Fe and Mn has been recommended as the most suitable method for the management of micronutrients for the better nutrition of the crops. The average response of Zn application to cereals, oilseeds, and pulses was around 20, 18, and 24%, respectively. The average yield increase due to iron (ferrous sulfate) has been recorded as 450 kg ha−1 in chickpea, 780 kg ha−1 in wheat, and up to 1500 kg ha−1 in paddy. The average yield increase recorded in paddy and wheat is 360 kg ha−1 and 560 kg ha−1, respectively, due to Mn supplementation in Punjab. The average yield increase in cereals and pulses crops was recorded up to 400 kg ha−1 due to boron application in the northeast region. Cereals, mainly rice and wheat, are inherently very low in concentration of Zn and Fe in grain, particularly when grown under Zn- and Fe-deficient soils. Deficiency of these nutrients in soil is affecting crop productivity, quality of food, and human nutrition. In rice out of the total micronutrients absorbed by the crop, only 31% Zn, 33% B, 18% Fe, 9% Mn, and 67% Cu remain in grains, and they are removed from the field. In cereals, Fe uptake varies from 150 to 1200 g ha−1 year−1. Micronutrient malnutrition now afflicts over two billion peoples across the world which causes health problems especially in women and children in developing countries. Besides agronomic strategy, microbial and physiological interventions help to mobilize micronutrients from source to sink and resulted in micronutrient-dense grain production with an increase in crop yields which helps to combat malnutrition in animals and humans. Hence, there is need to improve micronutrient quality through fortifying the grains with micronutrients.