Erodibility and infiltration characteristics of five major soils of southwest Spain

Equations used to calculate erodibility in the Water Erosion Prediction Project soil erosion Ž . model WEPP are based on erodibility studies in the USA and may not function well in another Ž . region. This study was conducted to: i analyze erodibility and infiltration characteristics of some Ž . predominant soils of southern Spain, and ii test equations used to calculate interrill erodibility in the WEPP model on these soils. The five soils chosen for this study in Andalusia, southwest Ž . Spain, were: two terrace soils referred to as ‘Red and Yellow Alfisols’ , an alluvial soil Ž . Ž . Ž . ‘Fluvent’ , a shallow hillside soil ‘Inceptisol’ , and a cracking clay soil ‘Vertisol’ . A static, solenoid operated rainfall simulator was operated at an intensity of approximately 60 mm h during a 60-min dry run followed by a 30-min wet run the next day on 0.75 m plots with 30% Ž ridge slopes. Infiltration rates were high always exceeding 50% except for the wet run of the . Ž y1 . Fluvent . The Fluvent had the lowest infiltration rate 0.00 mm min at the end of the wet run Ž y2 y1 y2 y1 . and highest soil loss 985 g m h in the dry run and 1557 g m h in the wet run . The Ž y2 y1 Vertisol, Inceptisol and Red Alfisol had low soil loss 415, 605, and 527 g m h in the dry y2 y1 . run and 824, 762 and 629 g m h in the wet run, respectively . Soil loss of the Vertisol doubled between dry and wet run and infiltration rate did not stabilize, suggesting that erodibility of Vertisols increases when they are wet. The Yellow Alfisol had lower final infiltration rate in the Ž y1. Ž y1. dry run 0.33 mm min than in the wet run 0.58 mm min and higher soil loss in dry run Ž y2 y1. Ž y2 y1. 1203 g m h than in wet run 961 g m h , the reason still being unclear. Soil loss was Ž . significantly correlated to siltqvery fine sand content rs0.96 , indicating that erodibility of these soils is determined by similar properties as soils in these soil orders in the USA. However, ) Corresponding author. Tel.: q1-814-863-7637; fax: q1-814-863-7043. Ž . E-mail address: [email protected] S.W. Duiker . 0341-8162r01r$ see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0341-8162 01 00145-X ( ) S.W. Duiker et al.rCatena 45 2001 103–121 104 Ž the equation for WEPP-interrill erodibility overestimated erodibility significantly two to four . times , indicating the need to develop new erodibility equations for the Mediterranean region. Infiltration rates were generally high and soil loss rates low compared to reports from the USA, suggesting that limited runoff generation is a primary reason for low erodibility of these soils. q 2001 Elsevier Science B.V. All rights reserved.