EFFECT OF ORGANIC MATERIALS ON PARTITIONING, EXTRACTABILITY AND PLANTUPTAKE OF METALS IN AN ALUM SHALE SOIL

Soils developed on sulphide-bearing shale (alum shale) in Norway conta in naturally high amount of heavy metals. We conducted a greenhouse po t experiment to study the effect of four rates (0, 2, 4, and 8%) and t hree sources (cow manure, pig manure and peat soil) of organic matter in partitioning and distribution, extractability and plant uptake of C d, Cu, Ni and Zn in an alum shale soil. Sequential extraction scheme w as used to determine the distribution patterns of metals in the soil. DTPA was used for extracting the metals from the soil. Wheat (Triticum aestivum) was used as a test crop to study the plant uptake of metals . The highest amount of Cd was present in the exchangeable fraction, i rrespective of the rate and source of organic matter applied. Copper, Ni, and Zn, on the other hand, were present only in small quantities i n this fraction. The largest fraction of Cu was associated with organi c matter and the amounts present in the oxide, carbonate and exchangea ble fractions were very small. Nickel and Zn were found mainly in the residual fraction. Increasing rates of cow and pig manure decreased th e amounts of Cd and Ni associated with the exchangeable fraction where as, the addition of peat soil at the same rate increased the amounts o f these metals associated with this fraction. This effect of organic m atter was primarily associated with the change in soil pH caused by di fferent organic matter sources. The DTPA-extractable metals were decre ased with increasing rates of organic matter application, irrespective of its source. Grain and straw yields of wheat were decreased with in creasing rates of organic matter. The application of organic matter in creased the Cu and Zn concentrations in both grain and straw. The conc entration of all metals was lower in plants grown in the cow manure am ended soil as compared to those grown in the soil amended with either pig manure or peat soil. These results suggest that the source of orga nic matter was a determining factor for metal distribution in the soil and for metal uptake by plants. In this study cow manure slightly inc reased the soil pH and thus was more effective than either pig manure or peat soil in reducing the plant uptake of metals but in general the efficiency of the organic material in reducing heavy metal uptake was small.