Agronomic Value and Environmental Impacts of Urban Composts Used in Agriculture
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-
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Introduction Composting represents a valuable alternative to incineration for organic waste elimination. Actually, less than 10% of the municipal wastes, including the green wastes are composted in France (IFEN 1999). However, this proportion should iINRA, Environment and Arable Crops, 78850 Thiverval-Grignon, France 2CREED, 291 Avenue Dreyfous Ducas, 78520 Limay, France 3INRA, Laboratory of Soil Analysis, 62000 Arras, France
H. Insam, N. Riddech, S. Klammer {Eds.} Microbiology of Composting © Springer-Verlag Berlin Heidelberg 2002
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increase since landfills are to be closed to recyclable wastes after 2002. Composts are mainly used as organic amendments rather than as fertilisers. Nevertheless, the availability of compost nitrogen and phosphorous must be known to adjust the mineral fertilisation to the crop needs and avoid nitrate leaching or excess phosphorous in soils. Many studies have been done on the agronomic values and the environmental impacts of composts on soil and plant quality (Stratton et al. 1995). Nevertheless, very few studies relate the results to the process of composting and compost physicochemical characteristics. This explains apparent contradictory results such as variable N availability in different composts, from 0 to 40% (Bernal et al. 1998; Mamo et al. 1999). On the other hand, maximum concentrations of heavy metals have been defined in France for sewage sludge but not for composts as in other European countries. The quality of the composts depends on the initial composted wastes and on the composting process. For example, the heavy metal concentration in compost is related to the waste sorting (Morvan and Carre 1994). Finally, very few data are available on the organic pollutants in composts (Berset and Holzer 1995; Niederer et al. 1995; Grossi et al. 1998) To provide guarantees on the safe use of urban composts to French farmers, a program has been initiated in which both the agronomic value and the environmental impacts of various composts are studied. This program includes the initiation of a long-term field experiment to point out effects of agricultural practices on soil and plant quality under conditions representative of the farmer practices (Chaney and Ryan 1993; Werner and Warnusz 1997). Long-term observations are also necessary to determine the capacity of compost to increase soil organic matter and modify all soil properties related to soil organic matter such as water retention, structure stability, Nand P availabilities. The first results of the field experiment are presented including: (1) compost characterisation, (2) soil initial analysis and evaluation of its homogeneity, necessary for the subsequent evaluation of the effects of composts and (3) results related to the first compost spreading, including an evaluation of the potential risk of soil quality degradation.
Materials and Methods The Composts Three urban composts were compared to a farmyard manure (FYM) as reference organic amendment: (1) a biowaste compost (BIO) issued from the co-composting
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