Evaluation of effect of soil organic matter on pores by 1H time-domain magnetic resonance relaxometry and adsorption-desorption of N2

Stabilization of organic matter (OM) is an important topic in soil science, but it is not yet completely understood. Recent interest in the recovery of poor or damaged soil with the addition of OM from waste such as paper mill sludge has led to further research on this topic. Research on the association of OM with soil minerals is difficult; therefore, most of the experimental studies published have been carried out on natural (not treated) or artificial soil. In this paper, we describe the use of both 1H nuclear magnetic resonance relaxometry in the time domain (TD-MRR) and N2 adsorption-desorption techniques to characterize samples of soil taken from a hillside treated with paper mill sludge. We have shown that although both techniques are sensitive to different, but to some extent complementary, scales of pore sizes, they can highlight the clogging effect of OM on soil pores (in a range of pores sizes from a few nm to several μm). The relations with total organic carbon were similar for the bound water porosity evaluated by TD-MRR and the specific surface area determined by N2 adsorption-desorption. This new approach that uses both TD-MRR and N2 adsorption-desorption also suggests that OM is well protected in small pores (≤ 2 μm), especially when there is preferential association with minerals, for example with kaolin clay and carbonates. Highlights: Characterization of the porosity of soil sampled from a hillside treated with organic waste. The combined use of 1H nuclear magnetic resonance relaxometry and N2 adsorption-desorption techniques. There is a clogging effect of organic matter on soil pores from a few nm to several μm. Both techniques can be used to add information on potential TOC stabilization