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.

As part of a study of recession farming on the 'fadama' lands on a segment of the Komadugu-Yobe floodplain, a survey was carried out to investigate the local farmers' perception of soil types and management practices. The farmers are clearly aware of the differences in soil type on the fadama and they possess unique skills in managing their farm lands. The farmers classifl fadama soils for recession farming by assessing soil texture and soil drainage conditions by feel and observation. Integrating such local knowledge into soil surveys will lead to better practical definition ofmapping units and give soil names that have more meaning for the farmers.

A series of five papers compares the cost-eflectiveness of different procedures for soil survey at medium scale. The first three are presented here.The whole trial area of 120 km' in Berkshire, in south-central England, was mapped in soil series by free survey at I : 25 ooo for publication at I : 63 360.

The requirement for revised asset management plans from water‐supply companies and the need to prioritize the renewal of buried water‐supply pipework has stimulated an interest in the spatial distribution of corrosion risk and intensity. This paper reports how the relationships between soil corrosion and the spatial distribution of soil types, as displayed on soil maps, can be combined to predict the likely incidence of aggressive soils and thereby identify those water mains which are most likely to need early replacement. The concept is illustrated by a project supported by Portsmouth Water plc.

A replicated, long-term field drainage experiment on a clay soil was started in 1978 to investigate the effects of mole drainage on land that had been direct-drilled or ploughed. We here describe the background and the need for this work, details of the experiment and summarize the results for the first 2 years. The main factors causing point-to-point variability in the soil at the experimental site and their relative contributions were assessed. Variations in inherent soil properties were small, except for depth to calcareous clay. Site hydrology was also generally uniform, especially soil water content, and was little affected by the presence of subsoil drainage schemes dating from the 19th century. There were some variations in micro-relief. The drained and undrained plots were hydrologically separated. Equipment was installed to measure separately surface runoff, lateral flow at the bottom of the cultivated layer (the interflow) and deep drainage from the mole and pipe system (in the drained plots only). The design and performance of that equipment is described. In both years much of the undrained soil became saturated in winter, but a residual cultivation pan limited the effect of the mole drains in 1978-9. In 1979-80, after disrupting the pan, the water table in the moledrained plots was about 25 cm deeper than in the undrained plots, root growth was greater and yield of winter wheat 11% heavier. About 90% of water and nutrients draining from the drained plots were carried in the mole and pipe system. The results on water balance, nutrient losses, crop growth and yield are fully reported in companion papers (Harris et al. 1984;Ellis et al. 1984).