SYSTEMATIC BIAS IN MEASURING INTENSITIES BY SELECTIVE EXTRACTION OF BULKED SAMPLES

The availability of an element in soil for plant uptake is quantified by its intensity. This is often assessed by using selective extractant s. Since bulking samples saves both time and expense, it is widely use d in the assessment of the average intensity of nutrients or contamina nts. Bulked samples and individual samples were compared for determini ng the extractability of an element. Simple mass balance calculations were used to compare the extraction efficiency of both bulked samples and individual samples. For a soil containing a linearly adsorbing sol ute the results showed that bulked samples, with different sorption ch aracteristics, may be systematically biased with regard to the arithme tic average derived from individual samples. Determination of P extrac ted with water (P-W), which depends on both intensity and quantity fac tors, confirmed that such a bias in soil samples may occur.