Author : Patcharesan Rujiyapanon

Summary : In very strongly acidic soils of the humid tropics, high concentration of aluminum is a major culprit in reducing crop yield. This investigation was conducted to evaluate the effectiveness of acidic soil solution as a screening medium for corn tolerance to acidity and high Al. The 1 N KCl and 0.1 M CaCl2 solutions at 1:2 ratio and unequilibrated were more suitable for screening corn tolerance to Al and acidity as the pH of the solution extracts were similar to that of the soil. The 0.1 M CaCl2 solution extract from Antipolo clay was more suitable for screening purposes than the 1 N KCl extracts as shown by the clearer distinction in the relative root length of the cultivars. The tolerant cultivars from the solution evaluation were IES No. 3, CW 58, P 30D44, IPB Var I, Tiniguib, USM 10, CW 98, CMU 12, P 3014 and P 3013 while IPB 911 and IPB 929 were intolerant cultivars. The tolerant cultivars which had lower yield reductions were associated with higher soil pH, lower exchangeable Al and solution Al. The intolerant cultivars IPB 911 and IPB 929 maintained higher shoot and root Ca concentration under the strongly acidic and high Al level of Antipolo clay. The cultivar IPB Var 1 contained higher P concentration in the shoot and root to overcome P constraints in extremely acidic Adtuyon clay. The cultivar IPB 911 with higher root weight reduction had higher Al concentration in the root than the other tolerant cultivars. On the extremely acidic Adtuyon clay, IPB 911 also had significantly higher Al than the rest of the cultivars except P 30D44 and IES No. 3. Grain yield reduction under very strong acidity and high level of Al was significantly lower with CW 58 at 20.4%. the cultivars IPB 911 and IPB 929 which were sensitive or intolerant cultivars had an average yield reduction of 45%. The ranks of cultivar tolerance in the soil solution extracts were not significantly correlated with their corresponding ranks in the pot experiment.