The effect of biochar, lime and ash on maize yield in a long-term field trial in a Ultisol in the humid tropics

A multi-season field trial was carried out to investigate the effect of the amendment of biochar, lime, ash and washed biochar on the growth of maize. A degraded, strongly acidic Ultisol (pHKCl 3.60), with a relatively high exchangeable aluminium content (2.4 cmolc/kg) and a low exchangeable calcium content (0.99 cmolc/kg), was used. Soil was treated once at the beginning of the field trial and crop growth was monitored over seven planting seasons (PS). All treatments increased maize yield. The average increases were; seven times for biochar, five times for lime, five times for washed biochar and eight times for ash treatment, when compared to the control across all PS. The effect of biochar, lime and ash treatments on maize yield were sustained over the seven PS. Soil pHKCl was significantly increased (p