Sparingly Soluble Powellite (CaMoO₄) as a Basis for Slow-Release Molybdenum Fertilizers: From Fundamental Principles to Performant Formulations

Molybdenum (Mo) is an essential plant micronutrient, required only in small amounts. Nonetheless, Mo deficiencies in crop production are not uncommon, and to avoid yield loss, fertilizers enriched with soluble Mo compounds are often supplied. However, the application of soluble Mo compounds is linked to low Mo use efficiencies due to fast Mo fixation in acid soils and leaching in sandy soils. This study explored sparingly soluble powellite (CaMoO4) in Mo-enriched granular fertilizers to regulate the release of Mo over time and supply available Mo throughout a crop’s growth period. Powellite was prepared via a simple precipitation reaction, and macronutrient carriers were cocompacted to pellets with either powellite or conventional soluble ammonium molybdate (amMo). In column dissolution experiments, powellite-based fertilizers consistently released Mo more slowly than corresponding amMo-based fertilizers, with the slow release notably more pronounced for powellite embedded in carriers with high content and solubility of Ca. A pot trial with chickpea demonstrated that powellite-based fertilizers can minimize Mo leaching in well-drained conditions in comparison with amMo-based fertilizers, while still acting as an adequate Mo source for crops. These results demonstrate how a desired Mo release can be obtained by selecting a suitable powellite macronutrient carrier, highlighting the potential of powellite-based Mo fertilizers for more efficient Mo use in crop production.