Layered Transition Metal Molybdates as New Slow-Release Micronutrient Fertilizer Matrices for Zn, Cu, and Mo

Micronutrient availability in agriculturalsoils is an importantdriver for crop production, and for mobile micronutrients, slow-releasefertilizers can more efficiently enhance crop nutrition. In this study,for the first time, layered transition metal molybdates (LTMs) areproposed as slow-release fertilizer compounds for the micronutrientsmolybdenum (Mo), zinc (Zn), and copper (Cu). A series of LTMs weresuccessfully prepared in varying synthesis conditions, characterized(inductively coupled plasma optical emission spectrometry, X-ray diffraction,Fourier transform infrared, and scanning electron microscopy), andtested for solubility in water. For three selected LTMs (Zn-Mo,Cu-Mo, and Zn-Cu-Mo), the solubility as a functionof solution pH was determined. The LTMs showed limited stability inacidic conditions. Therefore, co-compaction of LTMs with pH neutralor alkaline macronutrient carriers [muriate of potash (MOP), limestone,rock phosphate] was explored. A Zn-based LTM co-compacted in a MOPcarrier showed a useful slow and almost constant release rate of bothMo and Zn in a column dissolution test (Mo release reaching 32% after72 h), while a reference compacted MOP fertilizer with soluble Moreleased 90% of Mo after 4 h. Hence, a Zn-LTM could prove useful asa slow-release fertilizer or raw material to incorporate into non-acidicmacronutrient fertilizers.

Automated summary

Layered transition metal molybdates (LTMs) are proposed as slow-release fertilizer compounds for micronutrients molybdenum (Mo), zinc (Zn), and copper (Cu). LTMs were successfully prepared and characterized, and their solubility in water was tested. The LTMs showed limited stability in acidic conditions, so co-compaction with pH neutral or alkaline macronutrient carriers was explored. A Zn-based LTM co-compacted in a muriate of potash (MOP) carrier showed a slow and constant release rate of both Mo and Zn, making it a potential slow-release fertilizer or raw material for non-acidic fertilizers.