Slow- and fast-release magnesium-fortified macronutrient fertilizers improve plant growth with lower Mg leaching loss

The application of magnesium (Mg) fertilizer to alleviate Mg deficiency and improve crop yield has gained wide recognition. However, high Mg leaching loss is a growing concern in high rainfall areas, especially in acidic soils. Developing Mg fertilizer with less risk of leaching and adequate Mg supply to crops in a convenient way is worth considering in agricultural production.

In this study, five Mg-fortified mono-ammonium phosphate (MAP) fertilizers were produced with anhydrous magnesium sulfate (MgSO₄) and dolomite (CaMg(CO₃)₂) in various ratios. Nutrient solubility, Mg nutrient release, Mg leaching, and agronomic effectiveness under rainfall conditions in an acidic soil were evaluated.

Addition of the Mg sources to the MAP fertilizer did not affect P solubility of the fertilizer. The MAP fertilizers fortified with both MgSO₄ and dolomite showed an initially fast release of Mg followed by slower release. In a pot experiment with simulated rainfall, the amount of Mg leached significantly decreased with increasing proportion of dolomite in the Mg-fortified fertilizers, which varied from 19.1% for the MgSO₄ treatment to 3.8% for the dolomite treatment. Shoot dry matter yield and Mg concentration of soybean were higher for treatments with Mg-fortified MAP than for MAP-only.

The use of dual-release Mg sources in macronutrient fertilizers could be a promising strategy to better meet crop Mg demands and effectively reduce Mg leaching losses, especially in sandy soils of high rainfall areas.