Etude de l'incidence de l'apport de boues de stations d'epuration a des sols sableux sur l'evolution qualitative et quantitative de la matiere organique de ces sols

SIGLECNRS-CDST / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Dynamics of aggregate stability and biological binding agents during decomposition of organic materials

The relative importance of different binding mechanisms and associated biological binding agents on aggregate stability is still unclear. The aim of this study was to evaluate the role of various aggregate binding agents during the decomposition of cauliflower residues, wheat straw, cattle manure and poultry woody compost. We measured aggregate stability, hot-water extractable polysaccharide, C mineralization, fungal and microbial biomass dynamics in an amended silt loam soil, under controlled conditions. Soil aggregate stability was measured using three methods involving fast wetting, slow wetting and mechanical breakdown. Aggregate stability to slow wetting followed the same dynamics as C mineralization and was well correlated with polysaccharide content for cauliflower residues and wheat straw. This relationship is in agreement with the hypothesis that the rapid microbially induced improvement in aggregate stability that follows fresh organic residue additions at least partly involves labile polysaccharides. The transient increase in the two other types of stability was not directly related to C mineralization dynamics and seemed to be influenced by fungal hyphal length. Fungi would provide resistance to mechanical breakdown and slaking. The dynamic behaviour of biological binding agents was only partly explained by the initial quality of the organic materials, as characterized by Van Soest proximal fractionation

Compostage et valorisation par l'agriculture des déchets urbains

Urban composts constitute a valuable source of organic matter that can be used in agriculture, especially in areas where animal breeding has disappeared. Their use in agriculture is regulated through obligatory standards: NFU 44095 for sludge composts and NFU 44 051 for other organic amendments. These standards assure the innocuousness at short/medium term by limiting the concentrations in trace elements, in organic micropollutants, in pathogens and inerts. Some analytical methods of characterisation have been developed to predict their agronomic value. Long term field experiments are useful tools to evaluate the effects of repeated applications. From the results of the Qualiagro field experiment, the indicator ISMO seems valuable to predict the capacity of organic amendments at increasing soil organic matter contents. Repeated applications of composts have improved soil structure stability, stimulated soil microbial activity, and produced yields equivalent to mineral fertilization. The fluxes of trace elements have reached a few percents of initial soil contents before starting the experiment. After 10 years of experiment, no degradation of grain quality has been noticed nor accumulation of organic micropollutants in soil or sanitary degradation of soils.Les composts d'origine urbaine représentent une source de matière organique valorisable en agriculture, d’autant plus dans les zones où l'élevage a disparu. Leur utilisation en agriculture est réglementée par des normes rendues d'application obligatoire : norme NFU 44 095 pour les composts de boue, norme NFU 44051 pour les autres amendements organiques. Ces normes garantissent l'innocuité à court et moyen terme en limitant les concentrations en éléments traces, composés traces organiques, inertes et pathogènes. Des méthodes de caractérisation au laboratoire permettent d'évaluer leur valeur agronomique. Des essais au champ de longue durée permettent de mesurer les effets de leurs apports répétés. Au vu des résultats de l'essai Qualiagro en Ile de France, l'indicateur ISMO semble prometteur pour prédire leur capacité à entretenir la matière organique des sols. Les apports répétés de composts améliorent la stabilité de la structure du sol. Ils stimulent l'activité biologique, permettent d’obtenir des rendements équivalents à ceux obtenus avec une fertilisation minérale classique. Les flux d'éléments traces représentent quelques pourcents des stocks présents dans le sol avant épandage. Après 10 ans d'essai, aucune dégradation de la qualité des grains n'est mesurée. De même aucune accumulation de composés traces organiques n'est observée, ni de dégradation sanitaire des sols