Extremely severe gully erosion on arable, terraced red-yelow podsol at Pindorama (Sao Paulo State, Brazil) during a summer rainy period is described and analyzed. Research on soil erosion was begun in Sao Paulo State in the 1940s and as a result local knowledge exists for the construction of efficient terrace systems. In spite of the development of scientific expertise and promulgation of legislative norms, soil erosion control is still a great agricultural problem in this region.

The studied field is situated at 48° 55´ W and 21° 23´S. The erosion prevention system, built before soybean cultivation, consisted of terrace-like steps alligned parallel to the contour lines, made by mechanical digging and accumulating the excavated materials to form 90-110 cm high banks with 90-110. The field was inconveniently divided, because terraces were 100 to 150 m apart, while common guidelines recommended no more than 20 to 25 m distance to optimize erosion control.

During the first intense austral summer storms, prior to crop emergence, a surface seal crust developed and rills were incised into the soil. Sediment was first trapped at the terrace bank convexity, but after 120 mm cumulative rainfall, since seedbed preparation, terrace overflow was observed. Later on terrace banks were incised, so that a continuous network, consisting of both, epehmeral and deep gullies was developed. Deep gullying was documented after390 mm rainfall. A 15.3 ha slope representative of the upper hillslope environment was selected. Soil loss rate after 674 mm rainfall, i. e. 2 months since seedbed preparation, was as high as 49,6 tm/ha. Sediment production by gully erosion represented more than 95% of the total soil losses due to concentrated erosion.