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Efficient and Environmentally Safe Use of Micronutrients in Agriculture

Abstract Micronutrient deficiencies in plants are common throughout the world. Many inorganic and organic fertilizers are manufactured and applied to soils and plants to correct micronutrient deficiencies. The objective of this article is to review current research and present our findings on factors that affect micronutrient fertilizer efficacy. In the United States, state laws regulate the “guarantee analysis” of fertilizers and essentially all states require that manufacturers meet a total analysis requirement. However, there is no consideration of micronutrient “availability” in this analysis. Our research has shown that Zn availability in granular fertilizer was related to water solubility (r2=0.92) and not total Zn content. The relative availability coefficients for organic and inorganic Zn fertilizers was also highly related to water solubility and independent of total Zn content. Because of this discrepancy, there are fertilizers in the marketplace that are very low in plant available micronutrients. In addition, some fertilizer manufacturing feedstocks contain heavy metals, which are transferred to the fertilizer and cause regulatory limits for heavy metal content to be exceeded. Canada has set limits for nine heavy metals: As, Cd, Co, Hg, Mo, Ni, Pb, Se, and Zn. Four states in the United States have also set limits for some heavy metals. Micronutrient fertilizer manufacturing and “guarantee analysis” should require certification to ensure that products reaching the marketplace are plant available and environmentally safe.