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Accueil du site → Doctorat → États-Unis → 1993 → Soil fertility and productivity aspects of alley cropping Leucaena leucocephala and Cassia siamea under semi-arid conditions at Machakos, Kenya

University of Florida (1993)

Soil fertility and productivity aspects of alley cropping Leucaena leucocephala and Cassia siamea under semi-arid conditions at Machakos, Kenya

Adan, Bashir Jama

Titre : Soil fertility and productivity aspects of alley cropping Leucaena leucocephala and Cassia siamea under semi-arid conditions at Machakos, Kenya.

Auteur : Adan, Bashir Jama

Université de soutenance : University of Florida

Grade : Doctor of Philosophy (PhD) 1993

Résumé
Soil productivity aspects of alley cropping under semiarid conditions were investigated in a three-year study at Machakos, Kenya. The objectives were to : (1) determine if alley cropping with leguminous trees and shrubs improves soil fertility and productivity, (2) separate the effects of mulch per se from those of in situ presence of the hedges, (3) assess the extent of tree-crop interaction patterns, and (4) determine the major factors that influence farmers’ adoption of alley cropping. The study consisted of Leucaena leucocephala and Cassia siamea alley cropped with maize (Zea mays) ; the woody species were also grown in sole-stand blocks outside the cropped field, their prunings applied as mulch to the cropped area in equivalent land areas. Difference in maize yield between alley-cropped plots and the plots receiving mulch from the block plantings showed that growing the hedges in situ had a positive effect on maize yield. Yield advantage of alley cropping over the separate crop and hedge planting systems, expressed as land equivalent ratios, were 36% and 12% for cassia and leucaena, respectively. Leucaena produced more biomass (4 t $\rm ha\sp-1$ $\rm yr\sp-1)$ than cassia (2 $\rm ha\sp-1$ $\rm yr\sp-1) ;$ also leucaena had higher fine-root density than cassia in the top soil (0-40 cm). Therefore, leucaena was more competitive than cassia, and over the years, maize yield declined by 12% under leucaena whereas it increased by 8% under cassia. For both species, maize nearer the hedgerows yielded more than those away from them. Soil water content was also higher near the hedgerows. Chemical and physical properties of the top soil (0-20 cm) did not differ significantly between treatments (with or without mulch or alley cropping) or over time for a given treatment. The quantities of mulch produced by the hedgerows were generally low, and they decomposed quickly (half life of four weeks) ; these could be the main reasons for the lack of significant changes in soil properties. Farmers were generally more interested in the fodder than the mulch aspects of alley cropping. Because of the initial high investments of inputs such as labor and seedlings that are required to establish the hedgerows, alley cropping is more likely to be adopted by relatively resourceful farmers such as coffee growers than by poorer farmers.

Mots clés : Agroforestry / Soils / Leucaena leucocephala / Cassia siamea / Maize / Coffee / Machakos, Kenya

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Page publiée le 22 septembre 2010, mise à jour le 24 décembre 2018