Spatial variation of root-zone and shallow vadose-zone drainage on a loamy glacial till in a sub-humid climate

Abstract

Drainage through the root zone at 1.06 m ( D 1.06) and through the shallow vadose zone at 1.83 m ( D 1.83) was measured for three years on three monitoring sites on a 12 m × 12 m loamy glacial till experimental unit, under a crop rotation of wheat, sunflower, and soybean. Large local differences in D 1.06 were caused by very small differences in land surface elevation (less than 3 cm) between measurement sites, rather than by variation in soil hydraulic properties. Microtopographic surface elevation differences caused water to concentrate in local sites of high surface infiltration activity. Water then drained through highly active sites to the water table (at about 4 m depth), redistributed laterally to positions underlying sites of lesser surface infiltration activity, and moved upward into vadose and soil zones. Capillary waters later redrained as the water table receded. Crop growth characteristics, including the nature and timing of canopy and root formation influenced the local recharge activity of local measurement sites.