Short-term dynamics of soil aggregate stability in the field

Aggregate stability is a key property affecting the movement and storageof water, seedling emergence, and soil sensitivity to erosion. Many studieshave shown that aggregate stability changes through time. Field monitor-ing studies performed with a relatively large (monthly) time step showed theseasonal trend of aggregate stability. However, shorter time step monitor-ing is required to explore dynamics of aggregate stability at short term. Fornow, biological activity was recognized to be the main factor of aggregatestability dynamics, but previous studies were currently based on the externalstimulation of aggregate stability. The objectives of this study were to assessvariations in aggregate stability at short time steps in the field and to identifythe factors controlling these variations of stability. A 6-mo field monitoringwas performed at short time step (2–5 d) on a bare field of Luvisol withoutorganic amendment. Aggregate stability was measured for both on surfaceand subsurface materials by the ISO 10930 (2012) method. Rain amount andintensity, air temperature and humidity, soil temperature, water content andhydric history, and soil water repellency were measured as explanatory fac-tors. The results showed that aggregate stability varied greatly (up to 40%)over a few days for both surface and subsurface. Short term dynamics ofaggregate stability were already shown by laboratory experiments, but suchdynamics was never observed in the field for a bare soil without externalstimulation of biological activity. For the surface, short time step variationsof surface aggregate stability were primarily controlled by soil water content(WC0 and WC1/2), hydric history (DWC4 and API), and rain intensity. Whilelarge changes in aggregate stability were found for the subsurface, explanatory factors remain to be found.