A study of alley chopping maize and green gram with leucaena leucocephalla (lam) de wit at Mtwapa, Coast Province, Kenya
Crop yields in the Kenya Coastal lowlands are low because of poor soil fertility and high weed infestation. The sandy soils (92% sand), deficient in all major nutrients N,P,K, are highly leachable and" fertilizer application is necessary for good crop yields. Green' leaf Manure (GlM) from Leucaena leucocephala hedgerows (alleys) established in a split-plot systematic design with 5-replications were Incorporat.ed to boost soil fertility, by cutting them down to O.5m from the ground level 2 weeks before maize crop planting. Two additional cuttings were made during the cropping season for additional GUM and to minimize Leucaena shading on the crop. Assessment of crop yields and monitoring of soil fertility trends was carried out over a period of four years (1982-1985). It was observed that the usual trend of soil fertility decline that normally results with continuous cropping was reversed with the use of Leucaena alley farming. The system was even able 'to increase maize yield by 38% after four continuous cropping years, except for the period of tree establishment and pruning during which crops were significantly reduced due to excessive shade effect. Soil tests also showed a gradual increase in soil % organic carbon, phosphorus, potassium, calcium, magnesium and pH over the control plot's. This was due to the high organic N-additions , up to 283Kg N/ha from Leucaena GlM, nutrients release from tree root death and decomposition, and finally, nutrients savings from uptake by weeds. In general, the higher the tree density/ha, the higher the concentration of soil nutrients including an increase in soil pH. Significant weed cqntrol of upto 90% was achieved due to the fallow effect preceding the alley cropping. Besides, most of the difficult to control grass weeds were reduced in favour of the easier to control broad-leaved, non-grass weeds. The Financial returns and savings from the sale and use of fuelwood and GLM to the system were also remarkably high. cuttings during one cropping season yielded 28.3 t/ha of fresh GLM.