Light textured sandy soils are ubiquitous throughout the tropics and constitute an important soil resource on which millions are dependent upon for their livelihoods. Spanning a range of rainfall regimes from the arid to the humid tropics, they present unique sustainability and environmental challenges to resource managers. Over the course of the symposium papers were presented on topics that focused on the physical, chemical and biological attributes of these soils as well as the important social and economic consequences of utilizing this resource.
Sandy soils are characterised by the predominance of rigid coarse particles that are inevitably associated with small amounts of clay minerals. These physical attributes contribute to the significant spatial and temporal variability that offers opportunities for greater use of spatial statistics in managing this variability. The inability of these soils to buffer changes in physical, chemical and biological predisposes them to accelerated rates of degradation.
A common thread in all of the presentations highlight large differences in soil behaviour associated with minor changes in intrinsic soil properties that cannot be entirely attributed to natural heterogeneity. This may in part be due to the precision and quality of analytical tools used to quantify clay and organic matter quantity and quality, bulk density, pore size distribution or continuity, and sand size distribution. Improved sandy soils characterization would lead to a better understanding of processes of soil change, a better classification of relevant factors into a hierarchical system and finally, to more precise management recommendation that would enhance the sustainable utilization of these soil.
Physical, chemical and biological characteristics of sandy soils often act as a severe limitation in crop production. Their sandy nature; low organic carbon content; high hydraulic conductivity rates; low nutrient and water supply capacity; limited buffering capacity; and inadequate biological diversity invariable necessitate high levels of external inputs. This has potential environmental implications under high rainfall or irrigated agriculture, elevated costs of production and very low levels of efficiency. By manipulating the constituent components of the soil through the addition and conservation of organic matter or through the physical application of organic waste and clay materials, the potential productivity of these soils can be realized. There are thus significant opportunities in developing innovative management strategies that enhance the productivity of these systems under the diverse range of climatic conditions in which these soils occur.
Any innovation must integrate not only the limited potential of the tropical sandy soils but also the socio-economic situation of the farmers. Within the tropics, these soils are predominantly occupied by resource poor and often marginalized communities that have limited capacity to address the aforementioned biophysical challenges. There is an urgent need for the disciplines of soil science, agronomy and the social sciences to come together to address these challenges in a holistic manner that effectively result in uplifting the livelihoods of the poorest. This is by no means a trivial task, but one that takes innovation and commitment by governments and leaders.