By definition, erosion tolerance should consider the conservation of the soil as a natural resource essential for crop production. Erosion rates greater than soil renewal will cause soil depth loss. A minimum soil depth was defined as the depth in which the inputs (fertilizers, crop residues) and management technology (irrigation, improved genetic crop quality) were insufficient to prevent economic productivity loss. Thus, erosion rates greater than soil formation are acceptable only during the time in which the soil does not reach the minimum depth. We have defined this time period as life-time. The life-time concept was applied to the Ceveiro watershed (1,945 ha) located in a sugarcane growing region in the Southeast of Brazil Erosion rates were estimated with the Universal Soil Loss Equation and soil depths were measured by field surveys. Depth change and life-time calculations, considering a soil formation rate of 0.2 mm y-1, and assuming the present scenario of land use and a minimum soil depth of 1.0 m were made using the Geographic Information System. Land use represented 1,319 ha (68%) of sugarcane, 346 ha (18%) of forests and 278 ha (14%) of pasture. The area in which soil erosion was less than soil formation (not associated to long term impacts) represented 475 ha (24%), which included the total forest areas and 48% of pastures. The total sugarcane area had erosion rates greater than soil formation. The area with erosion rates greater than soil formation rates and soil depth less than 1.0 m, which resulted in a life-time equal to zero (soil erosion impacts are presently irreversible) was 832 ha (42%). This area was composed of 702 ha of sugarcane and 130 ha of pastures. The remaining area (erosion greater than formation and soil depth > 1.0 m) represented 638 ha (32%), which was composed of 620 ha of sugarcane and 18 ha of pasture. The half-lifetime for the watershed was estimated as 350 yr. The life-time concept was effective to evaluate the extreme soil degradation risk of the Ceveiro watershed in an integral and reliable form.
Erosion tolerance; life-time