FIELD-SCALE VARIABILITY OF CADMIUM AND ZINC IN SOIL AND BARLEY

CaCl2-extractable soil Cd and Zn contents have been suggested as a mea sure of bioavailability. To investigate the ability of this measure to reflect spatial patterns of Cd and Zn concentrations in barley (Horde um vulgare L.) in an arable field, plant and soil samples were taken f rom a 0.5 ha area sandy soil contaminated with Cd and Zn. Cd and Zn co ntents in barley and yield were spatially variable. Yield was low, whi ch may have been caused by Zn toxicity or atrazine turnover. For Cd, C aCl2-extractable soil contents explained only 17% of the variation in Cd contents in grain, and for Zn no significant correlation was observ ed. Nevertheless, surface plots of CaCl2-extractable soil contents and contents of barley grain illustrated their corresponding spatial patt erns. Despite the poor linear correlation between CaCl-2-extractable s oil-Cd and grain-Cd, a stochastic model for long term behaviour of Cd in field soils predicted observed variability in Cd contents of barley grain well from spatial variability of soil pH and organic matter con tent. The probabilistic model predicted behaviour of Cd in terms of pr obability, and was more appropriate than the deterministic approach.