Soil Wettability As a Function of Organic Matter Molecular Structure.

Fragile soils in semi(arid) regions are deteriorating under current management practices. An increase in water repellence is reported for soils from around the globe and is of special concern in semi(arid) regions where agricultural production is limited by water availability.

To address this issue, we tested the hypothesis that soil hydrophobicity has dual origin in (i) molecular structure and (ii) spatial orientation of OM molecules on particle surfaces.

We are among the few to use microphotography to quantify soil hydrophobicity by contact angle (CA) differences at the hydrophobicity tipping point. In conjunction, we used Pas-FTIR data to identify the ratio of absorbtion bands at two different spectral regions: hydrophobic functional groups, and hydrophilic functional groups.

Comparisons between Pas-FTIR data and contact angle differences at the tipping point supports our conclusion that robust forms of OM and soil moisture management are a promising option to ameliorate soil hydrophobicity at its origin.