The depth and productivity of chalky soils

Abstract

Abstract. In south‐east England, no relation between cereal yield and soil depth is shown by field estimates or harvesting microplots with depths to compact chalk of 23–121 cm. Differences in yield of ryegrass and wheat grown in cylinders containing artificial profiles with different thicknesses of topsoil, subsoil, chalk rubble and clean chalk from the Panholes series on Middle Chalk were attributed almost entirely to different amounts of nutrients. Chalk fragments supplied about 20% by weight of moisture to plants, and topsoil and subsoil about twice as much. Laboratory studies confirmed that fragments of Middle Chalk from near Wye (Kent, UK) hold about 20% water under tensions between 30 and 1500 kPa, but showed that topsoil and subsoil hold slightly less than this. The discrepancy in estimating water holding capacity arises because profiles over compact chalk drain only slowly from saturation. In this wet state they are very vulnerable to water erosion. It was also observed that ryegrass roots under water stress can penetrate well rammed chalk rubble, and that substantial amounts of water can rise 20 cm through solid chalk within a few days. It is concluded that soil losses resulting from erosion over normal porous chalks diminish cereal yields only slightly provided nutrient levels are maintained.