Can occurrence of soil hydrophobicity promote the increase of aggregates stability?

- The hypothesis was that the organic matter content is correlated with the soil hydrophobicity.
- The objectives were to determine the hydrophobicity and the relationship with soil properties.
- Hydrophobicity index is directly associated with high soil organic matter contents.
- Hydrophobic aggregates showed higher geometric mean diameter and aggregates stability index.

The soil hydrophobicity can be understood as soil water repellency or difficulty in wetness. This phenomenon is associated with the covering soil particles and hydrophobic organic compounds reducing the soil sorptivity and hence infiltration of water. The objectives of this study were to determine the level of hydrophobicity in the soil and assess its relationship with resistance and size distribution of water stable aggregates, particle size distribution and organic matter content of different soils in southern Brazil. Undisturbed soil samples were collected in different soil layers, 0-5, 5-10 and 10-20 cm, to determine soil sorptivity, geometric mean diameter and aggregate stability index while granulometric composition and organic matter content were determined using disturbed soil samples. The sorptivity test was conducted using a tension micro-infiltrometer, with two different liquids, distilled water and ethanol (95% v/v). The proportions of sand, silt and clay did not correlate significantly with the occurrence of hydrophobicity. In the hydrophobic soils, hydrophobicity index is directly associated with high organic matter contents and did not correlate with the particle size distribution. For the hydrophobic aggregates, cohesive forces between the particles acted for long period as a result of slow wetting, which led to an increase in geometric mean diameter, stability index of water stable aggregates and consequently greater resistance to the disintegrating actions of associated agents.