Solid-Phase Speciation and Water Solubility Relationships of Zn in Zn-Enriched Ammoniated Phosphates.

Zinc (Zn) is an essential micronutrient for plants and humans. Millions of hectares of agricultural land are affected by Zn deficiency and it has been estimated that about one-third of the world's population is Zn deficient. One of the strategies that has been successfully used to tackle Zn deficiency is the application of Zn fertilizers, such as zinc sulphate (ZnSO₄·xH₂O – highly soluble in water) or zinc oxide (ZnO – nearly insoluble in water). Cogranulating a Zn source with a macronutrient fertilizer has been shown an efficient way to avoid not only the granule segregation, but also the poor Zn spatial distribution in the field, very common issues when Zn is bulk blended with NPK formulations. However, cogranulating Zn with phosphorus fertilizers can reduce effectiveness due to formation of insoluble Zn phosphates, but various technologies are becoming available to circumvent this issue. In this work we present and discuss the impact of the Zn speciation and water solubility in Zn-enriched phosphate fertilizers.