Diagnosis of the Accelerated Soil Erosion in São Paulo State (Brazil) by the Soil Lifetime Index Methodology

The soil is a key component of the Earth System, and is currently under high pressure, due to the increasing global demands for food, energy and fiber. Moreover, the management of agricultural systems is often inadequate and ignores the agricultural suitability of lands, and particularly the vulnerability of soils. This paper demonstrates the application of the concept of the Soil Lifetime Index (SLtI) for the entire state of São Paulo, at a spatial resolution of 30 m. The SLtI methodology represents a tolerance criterion and a diagnostic tool to assess the level of soil degradation by water erosion, based on estimated soil loss rates and on an average soil renewal rate. Two approaches were applied to determine: i) the remaining time (years) until the solum (horizons A + B) is removed by water erosion to a critical depth of 1.0 m (original approach); ii) the remaining time (years) until the top 0.25 m of the nutrient-rich soil surface is removed by water erosion (new approach). Several areas in the state have reached a very critical soil depletion level, due to the predominance of consolidated agricultural activities, mainly of sugarcane and livestock production (as in the mesoregions of Ribeirão Preto, Bauru, Assis, Itapetininga and Araraquara). Only 35 % of the study area is in conserved state; 65 % of the study area is in the state of resource degradation, requiring intervention to diminish soil loss rates - and of this total, SLtI is zero in 1 and 0.25 % of the study area, respectively, for the original (critical depth of 1 m) and the new approach (0.25 m). It was estimated that at the current soil loss rates, within 100 years, 20,000 km2 of the total area of the state of São Paulo (248,209 km2) will have reached the critical depth of 1.0 m, and the top 0.25 m of the soil surface from an area of approximately 76,000 km2 will have been completely removed if the current pace of resource exploitation is maintained.