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

Abstract

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.