The influence of traditional steep land agricultural practices on runoff and soil loss

The erosion of soil from subsistence agricultures on lands with steep slopes and shallow soil is poorly documented, particularly in Brazil. This paper details the hydrological and soil loss responses to traditional agriculture (shifting agriculture) of a steeply sloped sector (32° incline) classified by FAO has having Regosol soil. This sector is in Guarapuava, Brazil and is covered by a shallow, clayed soil that originates from basalt rock. All measurements were carried out between May 2003 and April 2004. Three replicate plots were established at three randomly selected land sites, which were under different phases of the rotational cycle: burned, fallow or shrubs. A total of 76 natural rainfall events were measured throughout the study period and the accumulated precipitation was 1538.9 mm. Rainstorms ≥30 mm were important for runoff and soil loss. The average runoff (expressed as a proportion of the total rainfall) over the 12-month investigation period for each of the three sites was determined to be 2.4%, 1.0%, and 1.4% for burned, fallow, and shrubs, respectively. The response to rainfall during the measurement period differed completely at each site. The average soil loss was as follows: for shrubs, fallow, and burned sites, average loss was 1.2 t/(ha year), 5.1 t/(ha year), and 6.1 t/(ha year), respectively. The results suggest that fire and traditional agriculture tillage practices affected the topsoil. Shifting cultivation patterns in the steeply sloped sectors cause a succession of high, intermediate, and low soil loss regimes, which are important for understanding contemporary landscape dynamics and land degradation in the Guarapuava region.