EVALUATION OF CRUSTING APTITUDE ON SIEVED SOILS. ANEWAPPARATUS

Soil surface crusting has severe agricultural and environmental effects. The action of beating rains can destroy soil surface structure and in some cases lead to surface sealing and crusting which, in turn, reduce soil conductivity, seed emergence and increase the runoff hazard. The susceptibility of different soils to crusting was studied by a new experimental apparatus and model. A micro rain – simulator mounted on a rotating disc sprinkles water on soil sample and after a certain time (or revolutions of the disc) the water ponded on soil surface completely percolates and water is again applied to the soil surface. The model was used to follow the variation of soil hydraulic conductivity as a function of time or total water applied during the crust formation. The effects of soil sieved crumbs and duration of pre-saturation were investigated during the crust formation. For some soils crusting decreases along the sprinkling events, with the diameter of aggregates presenting high values; sometimes significant structural deterioration in the aggregate of higher diameter occurs after a initial resistance to crusting as evidenced by a sharp reduced hydraulic conductivity. The role of the pre-saturation time seem more important for less resistant soils.