On-Farm Productivity of Relay-Cropped Mucuna and Lablab in Smallholder Crop-Livestock Systems in Northwestern Kenya

Abstract

ABSTRACT Declining soil fertility and limited quantity and quality of livestock feeds are major constraints to agricultural production in northwestern Kenya. Legumes used as green manures may aid in overcoming soil nutrient depletion and lack of fodder. Relay-cropped mucuna (Mucuna pruriens (L.) DC. var. Utilis (Wright) Bruck) and lablab (Lablab purpureus (L.) Sweet cv. Rongai) were evaluated as alternatives to dry season, natural fallow for sustaining soil productivity in a maize (Zea mays L.)-common bean (Phaseolus vulgaris L.) intercrop on farmers' fields in northwestern Kenya. Four treatments were the factorial combinations of the two legumes and two levels of legume defoliation (none, or herbage above 10 cm removed prior to incorporation of remainder). Three controls were cattle manure (5 Mg ha−1), inorganic N (30 kg ha−1), and natural fallow. Undefoliated mucuna (UD-M) yielded more biomass (2.3 Mg ha−1, mean of two seasons) than undefoliated lab-lab (UD-L; 0.8 Mg ha−1) under the relay intercrop, contributing more nutrients to succeeding maize than lablab. Defoliation of the legume green manures removed on average 0.9 Mg ha−1 yr−1 of high quality top-canopy herbage. Nitrogen contribution ranged from 6 kg ha−1 for defoliated lablab (D-L) to 65 kg ha−1 for UD-M. Maize grain yield was greater (P = 0.003) following incorporation of mucuna vs. lablab in both seasons. Defoliation of legume residues prior to incorporation decreased subsequent maize grain yield (3.19 vs. 2.49 Mg ha−1 following mucuna; 2.28 vs. 1.92 Mg ha−1 following lablab). Relative to the natural fallow control, UD-M, defoliated mucuna (D-M), and UD-L resulted in 52, 34, and 14% increases in subsequent maize grain yield. In conclusion, relay cropping green manure legumes, particularly mucuna, has potential to increase subsequent maize grain yield even when some of the fodder is used as livestock feed.