An estimate of the uptake of subsurface soil potassium by crops in two long-term experiments

Plant roots may extend as far or farther below the ground than the plant does above. Given ample space the root system of a single plant may have a total spread of 1·2 m in wheat and 2·4 m in maize. Although a major part of the nutrients are absorbed by crops from the surface soil, subsurfacesoil contributions are often substantial. Part of the nutrients applied to surface soil may leach down and accumulate in subsurface horizons which are often exploited by the deep-rooted crops in a crop rotation (Sparks, Martens & Zelazy, 1980). Lysimeter and soil sampling studies have shown a reduction of K movement when soils are cropped (Broadbent & Chapman, 1949; Singh & Brar, 1977). The amount of reduction varies with the crops. Volk (1940) found that losses of applied potassium on a sandy soil over an 8-year period were reduced by 20% by growing a winter legume in the rotation.