Analytical Characterization of Composts of Different Origins: Agronomic Properties and Risk Factors of the Environment

Ten samples of compost produced in Italy were analysed for fertilizing elements and heavy metals. Different extraction methods [H2O, NaNO3, EDTA, DTPA and potassium pyrophosphate (K-Pyr)] were compared as indicators of heavy metal availability to plants. There was a high variability in composition even with composts of similar origin. Compost is comparable to farmyard manure (FYM) in organic content but has lower potassium and higher ash and silica contents. In most cases the concentration of metals is below the limits imposed by Italian regulations for town refuse compost, however, not all samples had sufficient organic matter, total nitrogen or potassium and some exceeded the C/N ratio. K-Pyr was the most effective extracting agent collecting up to half the total metals. EDTA Was more effective than DTPA, while H2O and NaNO3 extracted very low percentages of the total metals.