Crop response to fine and granular magnesium fertilizers

Abstract

Response of corn (Zea mays L.) to fine and granular Mg fertilizers was determined on an acid, Mg-deficient Weston fine sand (Typic Ochraquults) in a greenhouse pot experiment. Corn forage yields were similar with finely ground (< 0.2 mm) MgSO₄, MgO, MgCO₃, and Mg-oxysulfate (a partly acidulated MgO product). Granular MgSO₄ (100% water-soluble) was as effective as the finely ground products. Forage yields with granular MgO and Mg-oxysulfate were related to their granule size. Small (1.4 to 2.0 mm) granules were almost as effective as the finely ground fertilizers, but medium (2.4 to 3.4 mm) and coarse (3.4 to 4.8 mm) granules were increasingly less effective. Magnesium uptake by corn generally increased as forage yields increased.

After the first crop harvest, the soil was kept moist for 16 weeks. More NPK fertilizer was applied and the soil in each pot was mixed and repotted. A second crop of corn was grown to determine residual effects of the applied Mg fertilizers. Forage yields were similar with all granular and finely ground Mg fertilizers. These results suggest that while immediate availability to plants of relatively insoluble MgO is inversely related to granule size, residual availabiity of all granular and finely ground fertilizers was similar. Such granular Mg fertilizers could be bulk blended with NPK fertilizers to maintain available Mg levels in soils.