SOIL TRAFFICABILITY IN SPRING. 2. PREDICTION AND THE EFFECT OF SUBSURFACE DRAINAGE
Effects of subsurface drainage on trafficability of farmland were assessed over a 2-yr period. When compared with undrained land, drainage by drains spaced at 30.5 m resulted in earlier trafficability by 2–4 wk in a silty clay loam and by up to 5 wk in a muck. Halving the spacing did not increase benefits. Drainage intensity exerted its greatest influence on trafficability when the intensity was low, that is, at large drain spacings. Prediction of trafficability by two procedures revealed close agreement with one another and compared extremely well with dates on which measured water table depth and soil water tension were considered by farmers to be adequate for trafficability. Key words: Trafficability prediction, subsurface drainage, drain spacing, drainage intensity