LAUSR

Purpose Subsurface soil acidity in conjunction with aluminium (Al 3+ ) toxicity is a major limitation to agricultural production globally. The conventional use of surface-applied lime is often insufficient at correcting subsurface acidity; therefore, new practices and ameliorants are required. Methods This 3-month leaching experiment investigated whether animal wastes and other novel ameliorants in combination with lime could improve alkalinity movement, leading to greater amelioration of acid subsurface soil layers compared with lime alone. Five ameliorants (mature dairy compost, vegetable garden compost, poultry litter, potassium humate and gypsum) were added at a rate of 18 mg dry matter g −1 to the topsoil layer either without or with lime (target pH 5.5). Results All ameliorants with lime improved alkalinity movement below the amended layer (0–10 cm), with pH increases of 0.03–0.10 units at 1 month and 0.02–0.20 units at 3 months. In comparison, the Al 3+ concentrations in 10–12-cm and 12–15-cm layers were significantly decreased by 2–5.5 μg g −1 . With lime, the improvements in alkalinity movement with ameliorants were in the order of gypsum > vegetable garden compost > potassium humate > poultry litter > mature dairy compost. Without lime, each amendment increased soil pH in the subsoil, with their effectiveness decreasing in the order of poultry litter > vegetable garden compost > mature dairy compost > gypsum > potassium humate. Conclusion Some organic amendments are effective in addressing subsoil acidity. When combined with lime, their additive effects are limited.