The effect of two tree species, karité (Vitellaria paradoxa) and néré (Parkia biglobosa) on soil condition, development and production of cotton, sorghum and pearl millet, main crops in South Mali, has been investigated.
The soil under the trees is slightly richer (organic matter content and several cations) compared to adjacent tree-less sites. Also tree-specific effects exist.
Soil enrichment, however, is mainly a matter of redistribution of locally available nutrient resources.
Of the six associations studied, only karité-cotton shows no tree-induced reduction in crop production. All other associations suffer greatly from reduced crop outputs caused by the trees, usually in the order of 60%.
There are at least two reasons that explain tree-induced yield reduction. Because of increased humidity in the immediate surroundings of trees, in both soil and air, lower numbers of crop plants survive up to maturity, presumably because plants are attacked by fungi. Secondly, crop plants that mature show reduced output because of inter-specific competition for light and nutrients.
In case of néré, in order to minimize the trees' negative influence lopping is advised. Such practice, however, is less suitable in case of karité, because of its assumed lower potential to regenerate, as compared to néré.
South Mali West Africa tree/crop interface Vitellaria paradoxaButyrospermum paradoxumParkia biglobosacotton sorghum pearl millet