Incorporation of green manure cover crops in maize based cropping system in semi -arid and sub-humid environments of Kenya

The study involved two experiments; the first experiment was at Machakos Farmers Training Centre (semi-arid) while the second was at Kabete Campus Field Station (sub-humid). The aim of the first experiment was to assess the effect of different residue management practices using green manure cover crop (GMCC) on maize yield. The treatments, which were repeated during the subsequent seasons were: maize without fertiliser, maize with fertiliser, maize intercropped with Lima, bean (Phaseolus lunatus), maize+Sunhemp (Crotalaria ochroleuca) and maize+Mucuna (Mucuna pruriens). The biomass obtained was either incorporated or left as surface mulch or removed during the subsequent seasons. The second experiment aimed at assessing the effect of short-duration fallows of green manure cover crops on maize yield. The species planted during the fallow period were Mucuna pruriens, Purple vetch (Vicia benghalensis) and Crotalaria ochroleuca. Two additional plots were planted with a pure stand of maize, with or without fertiliser. The biomass obtained after the fallow period was either incorporated in the soil, removed or left as surface mulch during the subsequent season when all the plots were planted with maize. Biomass accumulation during the first season of the first experiment ranged from 2.8 to 5.9, 5.6 to 18.5 and 11.5 to 20.9 t DM ha-I for P. lunatus, C. ochroleuca and M. pruriens respectively. Maize grain yields were generally higher in the incorporation followed by mulching. The removal treatment had the lowest yield. However, in seasons of low rainfall, the trend especially for mucuna changed, the mulching treatment gave the highest grain yield (4.01 t ha-I) followed by the incorporation treatment (1.90 t ha-I) and the removal treatment gave the lowest yield (1.51 t ha-I). The increase in yields in the mulched plots was attributed to soil moisture conservation. Biomass accumulation for the short duration fallows ranged from 2.0 to 15.6, 11.2 to 18.0 and 15.6 to 20.0 t DM ha-l for' V. benghalensis, C. ochroleuca and M. pruriens, respectively. Maize grain yield after residue incorporation was higher than from maize+fertiliser plots although no fertiliser had been applied in the former plots. Incorporating V. benghalensis and C. ochroleuca more than doubled the yields when compared with the control. Yield increments of 16 to 58% compensated loss of yields during green manuring.