Competition between six hedgerow tree species and mung bean (vigna radiata (L.) wilczek) in the mid-country intermediate zone

Abstract

Tree and annual crops in agroforestry systems compete for growth resources. The objective of this investigation was to partition the overall tree-crop competition into above-and below-ground components in contour hedgerow intercropping systems involving six tree species (Callianrlra calothyrsus, Desmodium ransonii, Flemingia macrophylla, Gliricidia sepium, Cassia spectabilis and Tithonia diversifolia) and mungbean (Vigna radiata) grown at Pallekelle in the mid-country intermediate zone (IM3) of Sri Lanka. Lateral extension of tree roots to the area occupied by mung bean was prevented by cutting 1.5 m deep trenches at 25 cm from hedgerows. Below-ground (root) competition was estimated as the yield difference between trenching (TR) and non-trenching (NTR) treatments. Above-ground (shoot) competition was estimated as the yield difference between the yields of a sole crop control and TR. Mung bean yield reductions due to above-ground competition was greater than those due to below-ground competition in all hedgerow intercrops except that involving Gliricidia in which the two components were approximately equal. Total competition (i.e. yield difference between control and NTR) and above-ground competition was highest by Cassia and lowest by Gliricidia. In terms of absolute yield reductions, below-ground competition was highest in Calliandra and lowest in Cassia. When computed as percentages of Lota) competition, the highest and lowest below-ground competition were shown by Gliricidia and Cassia respectively. Variations between hedgerow species in biomass production capacity, the amount of nutrients added to the soil through prunings and the synchrony of their decomposition with periods of nutrient demand of the crop could be possible reasons for the observed inter-species variation of above-and below-ground competition.