The effect of pruning mulch and chemical fertilizers on the productivity of maize in leucaena leucocephala alleys

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The study was undertaken in 1991 - 1993 at a time when it was recognised that crop production was declining in the country. This was attributed to reduction in soil fertility which was in turn linked to traditional agricultural practices like slash and burn which normally returned soil nutrients to the soil, and, shifting cultivation where soil fertility recovered during a fallow period. However the increase in population led to land scarcity to such an extent that shifting cultivation involved shorter fallow periods, lower soil fertility and therefore poor crop productivity. In some areas especially in the north, the problem of the reduced effectiveness of these practices to replenish soil fertility was such that some people were even migrating southwards to other parts of the country in search of more productive land where adequate food production could be more easily realised. Another problem which was noted was the dwindling fuel wood supplies from the forests, since collection was increasingly involving more and longer journeys yet the product obtained and sold was not only reducing in size but was also becoming more expensive, which lead to the extensive destruction of all types of vegetation and land degradation. When these problems were noted they led to the identification of Agroforestry as an intervention that could address both issues of, replenishing soil fertility, and, increasing fuel wood production on the farm, which in turn could also contribute indirectly towards reducing pressure on the natural forests. Hedgerow intercropping was selected for this study as an appropriate agroforestry practice for the issues mentioned. The study examined how, applying mulch on maize growing in two levels of fertilizers in a Leucaena alley affected its growth and yield. It also examined not only the competitive effects of a Leucaena hedge on the adjacent crops, but also how their presence on the same land contributed to the profitability of the system. Growth was evaluated through measuring heights at 30 and 50 days, and grain yield by weighing the actual harvest. Soils and leaf analyses estimated the contribution of mulch to the soil, and, the woody material of the pruning was used to assess in monetary terms the hedgerow contribution to profitability. The performance of maize was found to be highest in plots with mulch, and, mulch with fertilizer, and, lowest in plots without external inputs of mulch and fertilizer. The competitive effects of the hedge were evaluated through comparing the growth and productivity of maize plants growing “near” and “away” from the hedgerow. The presence of hedge effects on the intercrop were established when plants growing “away” from the hedge were noted to consistently perform better than plants growing “next” to the hedge. Alley cropping was found not only to have the potential to act as an improved bush fallow and therefore provide an additional alternative to practices of slash and burn, and, shifting cultivation, but also, when mulch and firewood contributions were taken into consideration the practice in totality was found to be profitable. This was because the mulch boosted crop yield, which with fuelwood, led to higher revenue. Alley cropping was found to be beneficial in Ghana like in other areas of West Africa.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of Master of Philosophy Degree in Agroforestry, 2000