Subsurface acidity and liming affect yield of cereals

Abstract

In 2 field experiments, varying lime rates were applied to acidic soils and incorporated to 10 or 20 cm depth by rotary hoeing. In Expt 2, soil was also limed in 10-cm layers to 40 cm depth, and the profile was reconstructed. The aim was to remove acidity as a constraint to plant growth. In both experiments, 3 cereal cultivars (1 barley and 2 wheat) of varying aluminium (Al) tolerance were sown. Grain yield was monitored in 4 seasons (Expt 1) or 5 seasons (Expt 2). Incorporation of lime to 20 cm rather than to 10 cm improved yields of the cereals in 2 of 4 seasons in Expt 1, and improved yields markedly in a drier season in Expt 2. In Expt 2, cereal yield was demonstrated to be a function of soil pHCa in both the 0-10 and 10-20 cm layers. There was no advantage of amendment to 40 cm depth compared with 20 cm depth at this site. At both sites, the 10-20 cm soil (corresponding to the upper A2 layer) was very acidic, and the incorporation of lime to 20 cm removed this barrier. The effect of amendment or pHCa increase in the 10-20 cm layer is clearest and most consistent for barley, the most Al-sensitive species, and least consistent for the tolerant wheat cultivars. It is probably not realistic in commercial agriculture to incorporate lime to 20 cm depth. The alternative strategies are to wait for the effects of amendment of the 0-10 cm layer to move down the soil profile, or to amend part of the soil below 10 cm depth by lime injection. Until the subsurface soil is amended, the best strategy is to combine surface liming (0-10 cm) with the use of Al-tolerant cultivars.