Soil pH, exchangeable aluminium and lucerne yield responses to lime in a South Island high country soil

A 2-year field experiment was conducted on a high country brown stony soil in the Lees Valley, North Canterbury. Two forms of lime (‘AgLime’ and ‘Quicklime’) were applied at 4 rates (0, 2, 4 and 8 t/ ha) and plots sown with ‘Grasslands Kaituna’ lucerne. Soil pH was strongly (R²=0.73) related to exchangeable aluminium (Al), with a sharp rise in plant-available Al levels below a pH of 5.8. Soil pH changes of 0.15 units/t lime applied in the 0-7.5 cm horizon, and lower, variable, pH changes in the 7.5-15 and 15-30 cm horizons were achieved. Soil exchangeable Al dropped to low levels (< 0.3 me/100g) at all liming rates in the 0-7.5 cm soil horizon, and had a moderate to low effect in deeper soil horizons. Increases in soil exchangeable Al below soil pH 5.8 were linear, increasing at 0.2 me Al/100g per 0.1 pH unit decrease in soil pH. Effects of lime form were unclear. Lucerne yields were often low, in the order of 700-1 200 kg DM/ha, and were not influenced by lime rates or soil exchangeable Al. Other, soil and climate variables are discussed in relation to current DM yields. Measurements at this site are ongoing.Ministry of Agriculture and Forestry (MAF) Sustainable Farming Fund (SSF; 09123)