Temporal and spatial variations in topsoil water repellency throughout a crop-rotation cycle on sandy soil in north-central Portugal

The aim of this study is to improve our understanding of the temporal and spatial variations of soil water repellency, in particular those of agricultural lands where its economic and environmental impacts can be particularly severe. Variations in Water repellency severity were studied with particular emphasis as to the role therein of the in icro- topographic differences between furrows and ridges. Topsoil Water repellency was monitored over a I-year period at about monthly intervals and on some additional occasions in an agricultural field involving three land-use phases (potatoes, maize, fallow) in the Dimas de Vagos area, north-central Portugal. Water repellency severity was measured in situ at soil depths of 2-3 and 7-8 cm using the molarity of an ethanol droplet (MED) test, and accompanied by soil moisture measurements using a ThetaProbe. Under potatoes as well as maize, these measurements were carried out on ridges and in furrows separately. The results confirmed the transience of soil water repellency, which changed markedly within periods as short as 2 weeks. Although substantial changes in water repellency severity occurred, repellency was present over a large part of the monitoring period under potatoes, maize and fallow. Repellency severity was found to regularly differ significantly between furrows and ridges as Well as between 2-3 and 7-8 cm depth. Soil moisture content was found to be an important factor, but by itself not sufficient to account for the observed temporal variations. Other temporally variable factors (e.g. microbial and root activity) might contribute to the variations in water repellency at this agricultural site under rotating crops. Copyright (c) 2007 John Wilev & Sons. Ltd.