Effets de boues mixtes de papetières fraîches et compostées sur l’agrégation du sol, l’inclusion et la minéralisation du C dans les macro-agrégats stables à l’eau

Abstract

Bipfubusa, M., N’Dayegamiye, A. and Antoun, H. 2005. Effects offresh paper mill sludges and their composts on soil macro- aggregates.Can. J. Soil Sci. 85: 47–55. Soil aggregation is influenced byphysical and chemical properties of organic materials applied tothe soil.The objective of this study was to evaluate the effectsof fresh paper mill sludges and their composts, and their applicationfrequency on soil aggregation, mean weight diameter of aggregates(MWD) and on the C content and C mineraliza- tion from water-stableaggregates. The experiment was established on a Le Bras silt loam(Humic Gleysol) under silage corn (Zea mays L.) production, and wasdesigned as a split-plot experiment with six treatments in the mainplots that were applied at two frequencies (annual and biennial)in the sub-plots. Paper mill sludges and their composts were appliedat 40 t ha–1 on a wet basis, alone or completed with 120 kg N ha–1.Those treatments were compared to mineral N fertilization (160 kgha–1) recommended for silage corn, and the control. Soil aggregationwas assessed by wet soil sieving on a nest of 5-mm, 2-mm, 1-mm and0.25-mm sieves. Soil C contents and mineralization were determinedon whole soil and on > 5 mm, 2-5 mm and 0.25-2 mm aggregate class-es. Fresh and composted paper mill sludges significantly (P < 0.05)increased the proportion of water-stable aggregates > 5 mm, the MWDof aggregates and the C content of aggregate fractions, comparedto the control and the mineral N fertilizer treatment. However, theabundance of > 5 mm aggregates and the MWD of aggregates were significantlydecreased when fresh paper mill sludges were combined with mineralN fertilizer, suggesting a fast mineralization of binding agents.In contrast, N fertilizer appli- cation has not reduced soil macro-aggregates>5 mm and the MWD of aggregates in paper mill compost treatments,probably due to resilience to degradation of humic substances broughtby the composts. On average, carbon mineralization was highest inall aggregates in soils with paper mill sludges, than for their composts,which suggests that paper mill sludge C was more labile than compostC. Therefore, more frequent fresh paper mill sludge applicationswould be necessary for a sustainable effect on soil aggre- gation.