Effects of mulch from 14 multipurpose tree species (MPTs) on early growth and nodulation of cowpea (Vigna unguiculata L.)

Leaf extracts and mulch from 14 MPTs were used to study their effects on ge rmination, initial growth and nodulation of cowpea. Aqueous leaf extracts o f 1/4, 1/2, 3/4 and full concentrations were added to cowpea seeds placed i n Petri dishes. In the pot experiment, cowpea was planted in plastic Dots f illed with 1200 g of soil, and mulch was either surface-applied or incorpor ated into the substrate at rates equivalent to 5, 10 and 20 tons . s ha(-1) . Leaf extracts from Gliricidia sepium, Senna siamea, Milletia thoningii, G rewia pubescens and Tetrapleura tetraptera reduced cowpea germination signi ficantly at concentrations above 25 % of the full concentration 7 days of i ncubation. Root length was also strongly reduced by extracts from Gmelina a rborea, Senna siamea, Alchornea coordifolia, and Tetrapleura tetraptera. Th ese inhibiting effects were also observed in the pots. Mulch incorporation significantly reduced growth and nodulation of cowpea in the pots. These re ductions were more pronounced with the incorporation of mulch from fast dec omposing trees such as Leucaena leococephala, Gliricidia sepium and Grewia pubescens. Although Leucaena luecocephala and Gliricidia sepium released mu ch nitrogen, they strongly reduced cowpea growth when incorporated. This ma y suggest that other reasons than N immobilization caused growth reduction when the plant residues were applied to cowpea.