Moisture distributions and wetting rates of soils at experimental fields in the Netherlands, France, Sweden and Germany

The variability of soil water content over short distances was studied at seven experimental fields, located in southern Sweden, eastern Germany, southern France, and in the Netherlands. The soils all in use as arable land, are a sandy soil, a stony sandy soil, a loamy sand, a sandy loam, and three clay soils. Samples with a volume of 100 cm³ were taken at close intervals in trenches at several depths to determine potential water repellency and soil water content. When dry, the topsoils of the Mellby site in Sweden (loamy sand) and the Vredepeel site in the Netherlands (sandy soil) are water repellent, whereas the soils at the other five sites are wettable, according to the water drop penetration time (WDPT) test. The variation in water content within short distances was high at most depths at all sites, with differences of 7 to 18 vol% within a horizontal distance of only centimeters to decimeters. Drier as well as wetter soil areas were visualized by contour plots of the soil water content distributions in the transects. Large differences in wetting capacity between samples taken in the topsoil and in the subsoil at several sites were assessed by measurements of the wetting rate. In many cases, subsoil samples wetted faster than topsoil samples. The severity of water repellency of sandy samples from the Vredepeel site increased remarkably at oven temperatures above 65°C. The wetting rates of dried samples from this soil were also evidently influenced by the oven temperature; samples dried at 25°C wetted immediately and reached soil water contents of 23 to 32 vol% within one hour, whereas samples dried above 85°C hardly wetted during 72 hours, as a result of the increased water repellency at higher drying temperatures.