Drainability of some Dutch clay soils: A case study of soil survey interpretation

Abstract

Riverine and marine non-calcareous Dutch clay soils have moderate limitations for use as grassland under existing conditions due to high ground-water levels in winter and early spring, which have traditionally been attributed to a very low K sat of the clay. Physical research, which used soil morphology to define sample size and soil maps to locate test sites within defined mapping units, showed that permanent high ground-water levels were primarily due to low hydraulic gradients and not to a low K sat. Well-maintained tile drainage, to be associated with low water levels in the ditches in winter, resulted in much lower ground-water levels in the soil, thereby effectively reducing use limitations imposed by existing conditions and improving soil suitability. The latter was specifically characterized in this study in terms of the assessment factor: “drainage status”. Tile drainage resulted in a significant increase of K sat which was thought to be due to increased drying and cracking of the relatively young riverine soil. In the older marine soils, the increase of K sat upon tile drainage was due to deep earthworm activity. Existing suitability can thus be improved by using appropriate technology, i.e., tile drainage associated with better water management. The detail by which the technology is defined in soil survey interpretation is critical. The detail should not exceed the generality-level dictated by the variability of regional field data.