Effects of wheel traffic on runoff and soil erosion in slopes cultivated with vineyards

Mechanization characterizes the vineyards of La Rioja, one of the most important wine regions in Spain. Farming operations (plowing, soil removal, herbicide and pesticide application, harvesting of grapes and its transportation, etc.) are carried out with tractors that usually move in the direction of maximum slope, generating wheel tracks approximately 50 cm wide and 5-7 cm deep. The displacement of tractors on plots leads to the compaction of the topsoil and the subsoil. On the other hand, the location of vineyard parcels on steep slopes favours the erosive impact of surface runoff. This paper provides information on the role played by wheel tracks on soil loss by runoff in vineyards. To obtain this information, rainfall simulations with different intensities were carried out. The results confirm that, with moderate and high rainfall intensity, the runoff starts earlier and reach higher values in wheel tracks, due to compaction of the topsoil. Differences between wheel tracks and interrills are less pronounced on sediment yield. These differences are minimal in high intensity storms, having the tractor tracks lesser importance in erosion. By contrast, the drainage micro-network of hillslopes, eliminated by tillage and reactivated by heavy rainfall, seems to have more impact on runoff and erosion. The results obtained with the rainfall simulation experiments shed light on the relationships between runoff, raindrop impact and suspended sediment transport.