Long-term soil quality decline due to the conventional tobacco tillage in Southern Brazil

Since 1970, most of the tobacco has been cultivated using conventional tillage system in Southern Brazil. Any long-term soil degradation assessment on tobacco crop has not been performed, particularly, focused on soil erodibility. The objectives of this study were to evaluate the aggregate stability, soil erodibility, and physico-chemical soil changes, as a function of the time of tobacco cultivation i.e. chronosequence (forest, 3, 10, 15, 20, 25, 30, and 40 yr). Several tests for aggregate stability, soil physicochemical, and soil organic matter determination were applied. The dry mean weight diameter of aggregate decreased more than twice from 3.6 mm to 1.6 mm. While the aggregate stability decreased five times from 36.7% to 6.8% following the tobacco chronosequence. The organic matter content decreased abruptly i.e. 57% under tobacco cultivation. Inversely, the pH, cations and particularly, phosphorous concentration, increased three times on older tobacco plots (≥ 25 yr). Surprisingly, an increase of 23% in silt size fraction due to re-organization of particles, makes the soil more erodible along the chronosequence. Forty years of soil cultivation with tobacco, using conventional tillage methods caused significant soil physical-chemical degradation. Therefore, a soil conservation policy must be adopted urgently on tobacco crop areas in Southern Brazil.Annex 1 Soil physical-chemical parameters assessed in the tobacco chronosequence