Spatial distribution of soil strength and water content as related to tractor traffic in a sloping vineyard

Alterations in soil structure due to compaction influence strength and water status, which in turn affect root and shoot growth and consequently crop production and environmental quality (e.g. Hakansson and Lipiec, 2000; Horn and Fleige, 2000 ). Morevover, these alterations affect transmission parameters (Ferrera and Lipiec, 2000) and tillage implement draught. Soil in vineyard is subject to frequent tractor traffic associated with tillage and chemical operations. Usually ruts produced by wheeled or crawler tractors in vineyards have permanent location near the vine rows and affect soil conditions within the root zone (Van Dijck and van Asch, 2002). In sloping vineyard with the direction of the traffic across the slope ground contact pressure beneath a running gear can be greater in lower than upper portions of the slope owing to tilt of the tractor. The extent and depth of the resulting compaction on spatial distribution of soil strength and other characteristics are dependent on whether soil is under grass or cultivated due to different internai strength and susceptibility to compaction. Useful tools in quantifying compaction effects are geostatistical techniques. The aim of this study was to determine the effects of tractor traffic across the slope on spatial distribution of soil bulk density, penetration resistance and water content under grassed and cultivated vineyard.