The effect of soil surface temperature on the growth of millet in relation to the effect of Faidherbia albida trees

Faidherbia albida is an important tree species in traditional agroforestry cropping systems of the Sahel. The enhanced crop growth under its canopy (the 'albida effect') has been attributed to increased soil fertility in the canopy zone, improved microclimate, particularly in relation to plant/soil water relations, and the fact that the tree sheds its leaves in the rainy season, which reduces shade and allows the crops to grow. The present studies demonstrate that shade-induced reduction of soil temperatures, particularly at the time of crop establishment, contributes to the better growth under these trees. Greater use of shade to reduce soil temperature to the benefit of crops is proposed. Vertical shade barriers were used to vary the soil surface temperature by varying the time that the soil was exposed to direct sunlight. Pearl millet (Pennisetum glaucum), sown in this range of environments, germinated and grew best in a partially shaded environment, but failed in fully exposed conditions; growth was inversely related to mean soil surface temperatures during seedling establishment. In a separate, concurrent study, at the beginning of the Sabelian rainy season, a nearly leafless tree canopy intercepted about half of the incoming radiation, which resulted in a decrease of up to 10°C in the maximum soil temperature at 2cm depth (depending on position relative to the tree and time relative to rain) during the seedling establishment phase. © 1992.