Agronomic Value and Environmental Impacts of Urban Composts Used in Agriculture

Abstract

Agronomic value and environmental impacts of three composts (a biowaste compost, BIO; a municipal solid waste compost, MSW and a compost made from green wastes co-composted with sewage sludge, GWS) are compared to those of farmyard manure (FYM) in a long-term field experiment located in Feucherolles (Yvelines, France) and initiated in 1998. The first compost spreading occurred in October 1998 and maize was sown in spring 1999. Short composting time (in MSW) induced a large residual biodegradability of the organic matter and a transitory nitrogen (N) immobilisation after compost addition to soil followed by a faster organic N mineralisation than in more stabilised compost. The lowest concentrations of heavy metals were observed in the BIO compost in relation with the sorting of the composted wastes. Very low concentrations of polycyclic aromatic hydrocarbons (PARs) and polychlorinated biphenyls (PCBs) were detected in the composts. Soil (loamy clay) was analysed before starting the experiment. All heavy metals concentrations were lower than the average measured in French soils. Lead and mercury presented the largest variability (25 and 16%, respectively). Organic pollutant (PAHs and PCBs) concentrations were also low. A gradient of concentration was observed with up to 126% variability of the initial concentrations. The heavy metal input associated with compost spreading represented less than 5% of the initial stock present in the soil. The inputs of organic pollutants were proportionally larger but the evaluation of the other sources of contamination (aerial origin, for example) would be necessary to quantify the impacts of composts. Less than 5% of compost nitrogen and phosphorous was used by the plants. No cadmium, lead or chromium were found in the grains. No significant effect of the organic amendments was observed on the heavy metal content in grains and stems.