EFFECT OF ORGANIC-MATTER ON THE DISTRIBUTION, EXTRACTABILITY AND UPTAKE OF CADMIUM IN SOILS

Distribution and plant uptake of soil Cd as influenced by organic matter and soil type were investigated in a greenhouse experiment. Three soils (a sand, sandy loam and clay loam) were used. The rates of organic matter in its moist state added were 0, 20, 40, 80, 160 and 320 g kg-1 of the air-dried soil on mass basis. Ryegrass (Lolium multiflorum L.) was used as a test crop. Soil Cd was analysed by a sequential extraction technique and by extraction with 1 M NH4NO3 and 0.005 m DTPA. The exchangeable fraction of Cd as determined by 1 M MgCl2 in the sequential extraction procedure increased, whereas the Fe-Mn oxide-bound fraction decreased, with increasing levels of organic matter addition in all three soils. The dry matter yields of ryegrass were not affected by the addition of organic matter, but the Cd concentrations in both cuts of ryegrass decreased with increasing amounts of organic matter added. The plant Cd was highly but negatively correlated to soil CEC. At any level of organic matter addition, the decrease in Cd concentration of ryegrass was in the order: sand > sandy loam > clay loam.