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Fluid Journal : Winter 2012
4 The Fluid Journal Winter 2012 Summary: Improving zinc (Zn) nutritional status of food crops by applying soil and/or foliar Zn fluid fertilizers offers a practical and rapid solution to the well- documented Zn deficiency problem in human populations. In target countries with high incidence of Zn deficiency, new fertilizer policies should be developed to promote the application of Zn-containing fertilizers to the soil and/or foliar application for a quick biofortification of food crops with Zn.The returns associated with Zn fertilization of food crops are expected to be very high with significant impacts on humanity and also crop production. Zinc deﬁciency represents a common micronutrient deﬁciency problem in human populations. The Fluid Journal • Ofﬁcial Journal of the Fluid Fertilizer Foundation • Winter 2012 • Vol. 20, No. 1, Issue # 75 Dr. Ismail Cakmak Zinc Fertilizer Strategy For Improving Yield Ashort-term and complementary solution for improving yield and grain Zn concentrations is required if we are to alleviate Zn deficiency-related problems in human populations. In this regard, employing sound agronomics (e.g., fertilizer strategy) offers quick and effective ways to biofortify food crops with Zn at desirable levels. Fertilizer strategy simultaneously also contributes to better yield, depending on the severity of soil Zn deficiency. There are several factors affecting the solubility and root uptake of Zn in soils as discussed below briefly. Chemical solubility. Increasing chemical solubility of Zn in the rhizosphere by adding different organic amendments into soils, shifting from mono-cropping into inter-cropping systems, and applications of Zn fertilizers to soil are well-documented agricultural strategies that can significantly contribute to root uptake and grain density of Zn. Organic materials. It has been well documented that addition of different organic materials into soils as compost or farmyard manures greatly contributes to solubility and spatial availability of Zn and also the total amount of plant-available Zn concentrations (e.g., DPTA- extractable Zn) in soils. Existence of a strong, positive relationship between soil organic matter and soluble Zn concentrations in rhizosphere soil was found in 18 different soils collected in Colorado, indicating the importance of organic matter in improving spatial availability of Zn to plant roots. Intercropping dicots. In the case of bio-fortification of dicots with micronutrients, intercropping dicots together with cereal species is a very useful practice as presented in Figure 1. Iron concentration in different parts of peanut plants is significantly increased by intercropping with maize plants, possibly due to the root-induced changes in solubility of micronutrients and/or increases in biological activity in the rhizosphere. Source selection. Application of Zn fertilizers or NPK fertilizers containing Zn represents a useful and quick approach to improving concentrations of Zn in food crops. Zinc can be directly applied to the soil as both organic and inorganic compounds. Zinc sulfate (ZnSO4) is the most commonly applied inorganic source of Zn due to its higher solubility and lower cost. Zinc can also be applied to soils in the form of ZnO and Zn-oxysulfate. A factor affecting the selection of the source of Zn fertilizers is how uniformly they can be applied to the soil. To ensure uniform application of Zn into the soil, Zn can be incorporated into, or coated on the granular nitrogen, phosphate and potash (NPK) fertilizers. In India, urea is the most commonly applied N fertilizer and a good option for enrichment with Zn. In various field tests conducted with wheat and rice in India, it has been demonstrated that enriching urea fertilizer with Zn up to 3 percent improved significantly both grain yield and grain Zn concentration (Table 1). In these experiments, ZnO and ZnSO4 have been used to enrich urea with Zn, and both Zn sources were similarly effective in improving grain Zn concentrations, although ZnSO4 always tended to be better than ZnO in increasing grain Zn and improving yield. Part 2
Early Spring 2012