In many areas of the tropics, soil nutrient depletion is a major constraint to food production. Performance of legumes relay cropped with a long-season maize (Zea mays L.) hybrid were studied to determine whether subsequent maize grain yield could be increased. Treatments were the factorial (2 × 2 × 3) combinations of two legume cropping systems [based on the legume used; mucuna (Mucuna pruriens (L.) DC. var. Utilis (Wright) Bruck) and lablab (Lablab purpureus (L.) Sweet cv. Rongai)], two levels of legume defoliation (none or herbage above 10 cm from soil surface removed prior to residue incorporation into soil), and three crop sequences (legume in first year only, both years and second year only). There were three controls; (1) 30 kg ha-1 inorganic N; (2) natural fallow and; (3) 5 t ha-1 cattle manure. Mucuna yielded more herbage in the leaf fraction than lablab (1.6 vs. 0.86 t ha-1), and defoliation resulted in lower (0.76 vs. 0.13 t ha-1) leaf biomass. Lablab accumulated more biomass in the stem than mucuna (1.8 vs. 1.3 t ha-1). Leaf N accumulation for the defoliated mucuna treatment (D-M) averaged 48% that of undefoliated mucuna (UD-M), but for defoliated lablab (D-L), the value was only 4% that of undefoliated lablab (UD-L). When legume residue was applied for two consecutive years, UD-L yielded higher (P < 0.006) maize grain than UD-M (6.72 vs. 4.46 t ha-1), and D-M resulted in higher (P < 0.028) maize grain yield than D-L (6.08 vs. 3.98 t ha-1). After 2 years of residue application, maize grain yield was greater for D-M than UD-M, but defoliation resulted in a reduction of maize grain yield under lablab treatments. The D-M (6.08 t ha-1) and UD-L (6.72 t ha-1) after 2 years of residue application, yielded higher maize grain yield than the natural fallow control (4.11 t ha-1). Residual nutrients from legume residue incorporation in March 2000 increased maize yield in the 2001 season over that obtained for a natural fallow. It is concluded that single-year or alternate-year intercropping of mucuna and lablab can increase subsequent maize grain yield, even when a portion of top-canopy legume biomass is removed as livestock fodder.
Key words: Residual effects, lablab, mucuna, residue quality, soil fertility, maize, bean.
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