Plant Residue Decomposition: Effect of Soil Porosity and Particle Size

The decomposition of organic matter is a biological process that depends on climatic and edaphic factors. Numerous studies have been done to determine the effect of environmental factors such as temperature (Kirschbaum, 1995), N availability (Mary et al, 1996), plant residue content (Reinertsen et al, 1984), water potential (Sommers et al, 1980) and oxygen concentration (Parr and Reuszer, 1959). Little information is available about the effects that different degrees of contact between soil and plant residues have on the decomposition of organic materials. This contact depends mainly on the physical and chemical characteristics of the residue and the physical properties (texture, structure, water content) of the soil. Previous studies have investigated the effect of residue particle size (Bremer et al, 1991; Jensen, 1994; Angers and Recous, 1997) and soil texture (Hassink 1992; Scott et al, 1996) on C decomposition, but further investigations of the interaction between these factors should improve the description of plant residue decomposition in C-N models. For instance, reducing the particle size of residues of high C:N ratio such as mature cereals, enhanced short-term C decomposition while it has nil or a reverse effect for residues of low C:N ratio (Bremer et al. 1991; Jensen, 1994, Ambus and Jensen, 1997; Angers and Recous, 1997). The main hypotheses invoked to explain these observations were that decreasing particle size of residues of high C:N ratio enhanced the availability of soil N to decomposing microorganisms, while for low C:N ratio residues, increasing contact enhanced the protection of C against biodegradation.