Structure of a silty soil in relation to management

Abstract

SUMMARY In the United Kingdom silty soils have been classified as unsuitable for direct drilling since these soils may produce seed‐beds that are inadequate for satisfactory crop emergence. This judgement was based on problems encountered in the first 2–3 yr of direct drilling as well as on an appreciation of soil physical properties. Longer‐term experimentation (10 yr) has indicated that, subsequent to that initial period, soil conditions after zero‐tillage are not a major limitation to growth of autumn‐sown cereals. This eventual parity between simplified and conventional tillage can be attributed largely to improvement in the surface of direct‐drilled land. In the tenth experimental year this layer comprised more strongly developed aggregates, of greater stability, than those from the annually ploughed soil. Porosity and soil strength measurements did not indicate that root growth would be severely restricted below this depth. When this soil was wet in winter it was weak and relatively unstable and so it would most likely be unsuitable for sequential direct drilling of spring‐sown crops. At the same site soil that had been continuously under grass throughout the same 10 yr period developed better structure than that in the arable area, in part because of a greater earthworm population and an increased organic matter accumulation. In any subsequent change to arable usage this improved structure would best be conserved by avoiding soil inversion and using direct drilling or some other simplified method of cultivation.