Hydrophobicity of organic matter in arable soils: influence of management

The affinity of soil organic matter for water influences resistance to microbial degradation, the rate of wetting and adsorption processes. Such properties play key roles in organic matter and microbial biomass dynamics, aggregate stability, water infiltration, leaching of organic and inorganic pollutants, chemical composition and the dynamics of dissolved organic matter (DOM). The hydrophobicity of the organic matter as a function of management have been studied in two soils with contrasting textures using diffuse reflectance infrared fourier transform spectroscopy (DRIFT). The results show that agricultural management clearly influences the amount of aliphatic C-H units and implicitly the hydrophobicity of the soil organic matter. A decrease of organic C due to management is accompanied by a decrease of hydrophobicity as well as of soil microbial activity and aggregate stability. The hydrophobicity index is a sensitive quantity to characterize the 'quality' of soil organic matter. DRIFT spectroscopy proves to be a rapid and reliable technique to determine quantitatively the hydrophobicity of soil organic matter.