Magnesium fertilizer combined with biochar improves soil magnesium availability by affecting soil magnesium form transformation and migration

Achieving long-lasting management of magnesium (Mg) on acidic soils is an important guarantee for the sustainable development of intensive agriculture to increase production and quality. In this study, we examined the synergistic effects of Mg fertilizer and biochar on Mg availability in two consecutive years of experiments, in which Mg fertilizer and biochar were added individually or in combination to wax gourd grown under Mg limitation on acidic soils in South China. The data revealed that the addition of Mg fertilizer gradually removed the dominant limiting factor by increasing the content of different forms of Mg (e.g., the exchangeable Mg content increased by an average of 32.1 %) and improved wax gourd yield. However, Mg application alone reduces the adsorption capacity of soil for Mg 2 + (adsorption capacity decreased by an average of 9.6 %) and increases the leaching risk, resulting in low availability of soil Mg. Strikingly, the addition of biochar synergistically improved the overall uptake of Mg, mainly by driving Mg form transformation through improved soil physicochemical properties while increasing soil adsorption capacity for Mg 2+ (adsorption capacity increased by an average of 15.1 %). Despite the significant enhancement in wax gourd yields following biochar application alone, there are still Mg limitations. On the contrary, the synergistic application of Mg fertilizer and biochar improved the physical and chemical properties of the soil and greatly increased the content of different forms of Mg in the soil and the adsorption capacity of Mg 2+ , so the Mg absorption and yield of wax gourd increased by an average of 87.5 % and 35.5 %, respectively. Our findings demonstrate that Mg fertilizers synergized with biochar can improve soil Mg availability by enhancing soil physicochemical properties and Mg form transformation and migration. Thus, synergy between Mg fertilizers and biochar may be an effective strategy to enhance the long-lasting supply of Mg to acidic soils in South China to improve crop productivity. • Individual Mg fertilization elevates soil Mg but reduces its adsorption, raising leaching risk. • Biochar boosts Mg availability by altering its morphological transformation through improved soil properties. • Mg fertilizer synergized with biochar can achieve a long-lasting supply of Mg to maximize wax gourd yields. • This study proposes an optimized Mg strategy for South China vegetables to balance availability with leaching risk.