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 germination, initial growth and nodulation of cowpea. Aqueous leaf extracts of 1/4, 1/2, 3/4 and full concentrations were added to cowpea seeds placed in Petri dishes. In the pot experiment, cowpea was planted in plastic Dots filled with 1200 g of soil, and mulch was either surface-applied or incorporated into the substrate at rates equivalent to 5, 10 and 20 tons . s ha(-1). Leaf extracts from Gliricidia sepium, Senna siamea, Milletia thoningii, Grewia pubescens and Tetrapleura tetraptera reduced cowpea germination significantly at concentrations above 25 % of the full concentration 7 days of incubation. Root length was also strongly reduced by extracts from Gmelina arborea, Senna siamea, Alchornea coordifolia, and Tetrapleura tetraptera. These inhibiting effects were also observed in the pots. Mulch incorporation significantly reduced growth and nodulation of cowpea in the pots. These reductions were more pronounced with the incorporation of mulch from fast decomposing trees such as Leucaena leococephala, Gliricidia sepium and Grewia pubescens. Although Leucaena luecocephala and Gliricidia sepium released much nitrogen, they strongly reduced cowpea growth when incorporated. This may suggest that other reasons than N immobilization caused growth reduction when the plant residues were applied to cowpea.