Calcium amendment strategies for alfalfa with biomass yield responses across contrasting soils and stand types

Alfalfa ( Medicago sativa L .) is a high-value forage crop with substantial ecological benefits, but it is particularly sensitive to soil acidity and nutrient deficiencies. While current fertilization guidelines in regions like Québec, Canada, favor raw limestone (CaCO₃) exclusively, other calcium amendments, including burned limes (CaO, Ca(OH)₂) and sulfate-based materials, are commonly used elsewhere and may offer agronomic advantages. However, their effectiveness may vary with soil texture, stand age, and application method. This study evaluated the impact of nine calcium-based amendments: raw lime, burned lime, and sulfate-based non-liming materials, applied at a uniform spring rate (3 Mg ha⁻¹ CaCO₃-equivalent or 1.2 Mg ha⁻¹ Ca for anhydrite) on two alfalfa stands (newly seeded: establishment vs. long-established: maintenance) and two contrasting soil textures in Québec, Canada. Agronomic performance was monitored over four consecutive growing seasons. Results revealed contrasting responses: The establishment of an alfalfa stand on clay loam soil showed no biomass yield response to amendments. In contrast, the long-established stand on sandy loam soil exhibited strong and lasting responses. Sulfate-based treatments (CHAC, anhydrite, and lime-anhydrite) increased biomass yields by up to 2000 kg DM ha⁻¹ compared with the control, with gains persisting for 4 seasons after a single application. Mixed lime treatments (CaCO₃+CaO and/or Ca(OH)₂) also outperformed raw lime without causing phytotoxicity. These findings highlight the need for stand age-specific calcium amendment strategies. Sulfate-based and blended formulations may sustainably enhance productivity in mature alfalfa systems on coarse soils. Exclusive reliance on raw lime may overlook the agronomic potential of alternative materials.