Opportunities and Constraints for Addressing Human Mineral Micronutrient Malnutrition through Soil Management.
J.M. Duxbury1, M. Bodruzzaman2, S.E. Johnson3, J.G. Lauren1, C. A. Meisner4, and R.M. Welch5. (1) Cornell University, 904 Bradfield Hall, Ithaca, NY 14853, (2) Wheat Research Centre, Bangladesh Agricultural Research Institute, Nashipur, Bangladesh, (3) International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines, (4) IFDC, Road 54A, House no. 2, Apt. no. 6, Gulshan 2, Dhaka, Bangladesh, (5) US Plant, Soil & Nutrition Lab., Tower Road, Ithaca, NY 14853
Mineral micronutrient deficiencies are widespread in both soils and people of South Asia. The Green Revolution focus on increasing staple crop productivity without considering impacts on human diets and nutrient intake has exacerbated human nutrient deficiencies of Fe, Zn and I, while intensive cropping has decreased the capacity of soils to supply Zn, B, Mo, Mn and Cu to crops. Soil fertilization has been the standard approach for addressing micronutrient deficiencies in crop production, while the medical approaches of supplementation and fortification are most widely used to address human nutrient deficiencies. Opportunities exist to "biofortify" the seed of grain crops through fertilization with micronutrients and thus link agricultural production to human nutrition. This type of intervention has the advantage that it reaches the large fraction of populations in developing countries that do not purchase processed foods. However, it does require the infrastructure to provide quality micronutrient fertilizers and widespread adoption of micronutrient fertilization practices. Not all micronutrients can be enriched in all grain crops. Previous research has shown that grain can be enriched with Zn and I but this is not expected for Fe due to the strong homeostatic control exerted on grain Fe content. In the present research carried out in Bangladesh and Nepal, foliar fertilization with a suite of micronutrients increased the zinc content of several wheat and rice varieties by a factor of 2 to 2.6, to almost 50 mg kg-1. This Zn level is similar to that in grain legumes grown in the region. Manganese and copper concentrations were increased only slightly in wheat (1.2-1.3 times) but to a greater extent in rice (1.5 and 3.2 times, respectively). The Mo concentration in control seed was almost 10 times lower in wheat than in rice, and both were substantially increased by foliar fertilization. Grain Fe concentration was unaffected by foliar fertilization with Fe. Soil fertilization with Zn, Mn, Cu and Mo led to significant enrichment of wheat grain with both Zn and Mo but only Mo was enriched in rice grain. Concentrations of Mn and Cu were not altered in either wheat or rice. The inability of soil fertilization to increase Zn concentration in rice grain was caused by a reversible decrease in Zn availability following flooding of soil. EXAFS spectral analysis suggested that Zn precipitates as a non-crystalline mixed Zn/Fe sulfide under reduced soil conditions. In contrast to results with wheat, soil fertilization with Zn had only a small effect on the Zn concentration in chickpea and lentil. However, fertilization of soil with B increased grain B concentration from 2-6 to 8-18 mg kg-1. Micronutrient enriched seed successfully addressed Zn and Mo deficiencies observed in production of rice and wheat and increased yields beyond those achieved by soil fertilization with micronutrients. The additional yield benefits were associated with positive effects on root health that increased seedling emergence, vigor and subsequent crop growth. Zinc was found to be the nutrient responsible for improved root health. Mean yield increases of 25% were observed in on-farm trials with micronutrient enriched seed for both rice and wheat. The dietary intake of Zn by Bangladeshi children, which is primarily from rice, does not meet the World Health Organization's recommended daily intake. The additional content of Zn in micronutrient enriched rice is sufficient to rectify this situation and could potentially have a major impact on diarrhea and respiratory infections in children if this food systems approach to human micronutrient malnutrition was adopted. The ability to increase Cu,B and Mo in grain crops also has positive implications for human nutrition.