Spraying for Leaf Spot and Liming Increase Yam (Dioscorea Alata L.) Yield

Abstract

When yams were not sprayed to control leaf spot disease caused by Colletotrichum sp. essentially no yams were produced regardless of lime rates. When leaf spot was controlled by spraying, yam yields increased with increasing lime rates up to 36 t/ha, the highest level tested. The combined effect of spraying and liming increased yields from 1.4 to 30.6 t/ha. Yields were increased threefold when Al saturation of the soil exchange capacity was decreased from 37% to 0 by liming. Yields were decreased by 30% when Al saturation of the soil was increased only from 0 to 9%, a level at which most crops will not show a response to Al. This decrease illustrates the extreme sensitivity of yams to exchangeable Al in the soil. Composition of the leaves 6 months after planting was affected neither by lime rates nor spraying. The pH, Al saturation percentage of the soil exchangeable capacity, and lime rates applied were closely correlated with yam yields.