The effects of slash burning on ecosystem nutrients during the land preparation phase of shifting cultivation

The most commonly observed change in soil following slash-and-burn clearing of tropical forest is a short-term increase in nutrient availability. Stud ies of shifting cultivation commonly cite the incorporation of nutrient-ric h ash from consumed aboveground biomass into soil as the reason for this ch ange. The effects of soil heating on nutrient availability have been examin ed only rarely in field studies of slash-and-burn, and soil heating as a me chanism of nutrient release is most often assumed to be of minor importance in the field. Few budgets for above and belowground nutrient flux have bee n developed in the tropics, and a survey of results from field and laborato ry studies indicates that soils are sufficiently heated during most slash-a nd-burn events, particularly in dry and monsoonal climates, to cause signif icant, even substantial release of nutrients from non-plant-available into plant-available forms in soil. Conversely, large aboveground losses of nutr ients during and after burning often result in low quantities of nutrients that are released to soil. Assessing the biophysical sustainability of an a gricultural practice requires detailed information about nutrient flux and loss incurred during management. To this end, current conceptual models of shifting cultivation should be revised to more accurately describe these fl uxes and losses.