Faidherbia albida in the West African Semi-Arid Tropics Proceedings of a Workshop 22-26 Apr 1991 Niamey, Niger

This workshop brought together scientists and development workers, primarily those working in the West Africa region, to: review past and present research findings on Faidherbia alhida; discuss development issues and "lessons learned" from past and present; list research priorities for the future; and promote collaboration between research and development programs. These proceedings summarize the state of knowledge on the species and provide a comprehensive list of ongoing research. Papers are divided into sessions on: botany and distribution; uses; genetics, provenance trials, and vegetative propagation; site effects, silviculture, and rhizosphere; and development issues. Recommendations from Working Groups for future research and multidisciplinary linkages are included

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 phas

Variability in the growth of faidherbia albida: The soils connection

Variability in the growth of Faidherbia albida (Del.) A. Chev. (syn. Acacia albida [Del.]) in the Sahelian zone of West Africa is a common observation. The “albida effect” has been attributed to the amelioration of soil chemical, physical, and microbiological properties by the direct action of the tree, resulting in enhanced crop production beneath the mature canopy. Crop yields within fields without F. albida can also be highly variable within short distances. A study was conducted to observe the association between the variability in soil properties and the variable growth of young (2-yr-old) F. albida trees planted at the ICRISAT Sahelian Center located near Niamey, Niger. The results of this study indicate that the variability in F. albida growth is caused, in large part, by variability in soil properties across relatively short distances. Good growth sites had higher clay contents and base saturations, and lower exchangeable acidity than poor growth sites within the field. The tallest trees in the field were associated with the proximity to abandoned termite mounds and other microhigh sites. Seedlings planted on sheet-eroded sites caused by runoff from micro-topographical high sites within the field grew poorly. The variability in F. albida growth in plantations within Niger is hypothesized to be due, in part, to preexisting soil conditions. These results also suggest that the albida effect might be partially caused by these preexisting “islands of fertility”. This site-determined variable growth of F. albida could be exploited with proper seedling placement strategie

Transpiration from a neem windbreak in the Sahel

Windbreaks are being recommended for many areas of dryland Africa, although their effect on the area water balance is unknown. This study shows that a linear relationship exists between the leaf area and stem basal area of young neem trees The relationship remains linear into the dry season with a constant slope and a changing Intercept. Transpiration from individual trees, measured using a heat pulse velocity recorder. was scaled up to a windbreak by normalizing with stem basal area. For the unstrwsed windbreak calculated transpiration rates were 29.2 dm3 day-1 m-1

An equation for the replacement value of agroforestry

This article examines some of the existing analytical tools which quantify both the ecological and economic aspects of intercropping decisions. The characteristics of tree crops are evaluated to determine how a specific tool, the replacement value of intercropping (RVI), could be modified to better interpret agroforestry improvements to bush fallow farming systems. The modified equation captures some of the potential production improvements associated with agroforestry by accounting for the fraction of time that a field is actually in production over the long run. The result is an improved estimate of the average annual difference between a tree/crop polyculture and a monoculture system which employs fallows.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41763/1/10457_2004_Article_BF00705151.pd

Biophysical interactions in tropical agroforestry systems

sequential systems, simultaneous systems Abstract. The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interac-tions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offse