Effect of moisture and disaggregation on the microbial activity of soil

Soil moisture and physical conditions may influence biological activity by affecting the habitat and conditions for the life of microorganisms. In this work, the dehydrogenase activity (DHA) of a vineyard soil was measured at different moisture conditions, in different aggregate size fractions, and after breaking the existing aggregates. The highest values of DHA (144 mg TPF kg⁻¹ day⁻¹) were found for the undisturbed soil at a suction pressure of 0.1 MPa, and decreasing values were obtained at pressures above and below that water potential. The disruption of the aggregates strongly reduced the biological activity at suction pressures under 0.1 MPa, but had no effect in drier conditions. Both in disturbed and undisturbed soil, an important part of the biological activity remained at high suction pressures (over 0.1 MPa), with DHA values around 50% of the maximum values. This shows that an important part of the soil microbiota is highly resistant to extreme drought conditions.