Effects of boron waste (BW) addition on the bioavailability of boron and magnesium during swine manure composting

• Changes of the boron fraction (B) and bioavailability were assessed.
• The BW addition increased the bioavailability of B and reduced the proportion of exchange Mg.
• Humification process controlling the change of bioavailability for B and Mg.

The improper disposal of boron waste (BW) would bring much trouble for environment, at the same time, BW with a higher content of boron (B) and magnesium (Mg) could be used as a fertilizer in B and Mg deficient soils. Therefore this study recommended a novel disposal method of BW by composting, and investigated the influence of BW additions (at rates of 2.5%, 5.0% and 7.5%, dry weight basis) on the bioavailability of B and Mg during aerobic swine manure composting. Results indicated that additions of BW increased the content of both B and Mg in different fractions. The proportion of B fractions in the final composted material supplemented with BW were: nonspecifically adsorbed B (NSA-B) > B occluded in Mn oxyhydroxides (MOH-B) > specifically adsorbed B (SPA-B) > residual B (RES-B) > B occluded in crystalline Fe and Al oxides (CRO-B) > B occluded in amorphous Fe and Al oxides (AMO-B). The addition of BW improved the bioavailability of B to plants and reduced the proportion of Mg in the exchangeable fraction. Spearman correlation showed that B and Mg bioavailability was associated with fulvic acid (FA; P < 0.05). This study suggested that the humification process changed bioavailable forms of B and Mg during co-composting.