Biophysical interactions in tropical agroforestry systems

Abstract

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 interactions 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 offset the large competitive effect of hedgerows with crops for water and/or nutrients. Whereas improved soil fertility and microclimate positively influence crop yields underneath the canopies of scattered trees in semiarid climates, intense shading caused by large, evergreen trees negatively affects the yields. Trees in boundary plantings compete with crops for above-and belowground resources, with belowground competition of trees often extending beyond their crown areas. The major biophysical interactions in improved planted fallows are improvement of soil nitrogen status and reduction of weeds in the fallow phase, and increased crop yields in the subsequent cropping phase. In such systems, the negative effects of competition and microclimate modification are avoided in the absence of direct tree-crop interactions.Future research on biophysical interactions should concentrate on (1) exploiting the diversity that exists within and between species of trees, (2) determining interactions between systems at different spatial (farm and landscape) and temporal scales, (3) improving understanding of belowground interactions, (4) assessing the environmental implications of agroforestry, particularly in the humid tropics, and (5) devising management schedules for agroforestry components in order to maximize benefits.

Influence of Re-Greening on the Infiltrability of Soils in South-Central Niger

“…This tendency was observed by Rao et al, [34] in the Kenyan Savanna. Lili et al [20] showed that the presence of vegetation is positively correlated with infiltration.…”

Soil bulk density and biomass partitioning of Brachiaria decumbens in a silvopastoral system

“…The significance and the level of competition are determined by climate, management, soil type and species. Although reductions in the soil water content under forests versus pastures may occur (Yunusa et al, 1995), in silvopastoral systems that are established in humid environments, the primary form of competition is for light (Rao et al, 1998). Maximum temperatures in the litter and on the surface of the soil under the shade were lower than the average values found under full sun in tropical areas (Belsky and Canham, 1994;Wilson, 1996).…”

Assessing the effect of Faidherbia albida based land use systems on barley yield at field and regional scale in the highlands of Tigray, Northern Ethiopia

“…A tree may modify or improve growth of another tree or crop by changing the bio-physical conditions and thus establish a better potential environment for the latter (Hunter and Aarssen 1988;Rhoades 1997). Trees can increase system productivity by reducing nutrient losses through leaching into the subsoil, reducing soil erosion, providing protection from wind erosion (Rao et al 1998), reducing weed populations, enhancing resistance to cyclic environmental changes, enhancing efficient utilization and recycling of resources (Liebman and Gallandt 1997;Ong et al 1996) and increasing available nutrients for crops by root exudates or rhizosphere effects (Radersma and Grierson 2004).…”