INFILTRABILITY AND MEASUREMENT OF PHYSICAL CHARACTERISTICS OF CRUSTS DEVELOPED ON WET OR DRY SOIL AGGREGATES UNDER SIMULATED RAINS [French]

摘要

The sealing of a soil surface under rain reduces the infiltrability of cultivated soils. This phenomenon is largely conditioned by the soil constitution and the initital water content These 2 factors were studied in the laboratory using a bed of soil aggregates. Silty (L) and a clay-silty (AL) soils were chosen. Soils were initially dry or wet and then received a series of rains (26 mm/h, 23 J/m(2)/mm). Between 2 subsequent rains, the infiltrability was measured under a large amount of water (120 mm/h, 3 J/m(2)/mm), in order to demonstrate that the reduction in the infiltrability occurs before the phenomenon can be actually measured under rain. Aggregates of the dry - L, dry AL and wet-L soils break into fragments. The wet - AL soil shows abrasion of aggregates. The reduction in soil infiltrability, which is related to crust formation, appears after a greater quantity of rains if the soil was initially wet than when it was initially dry. The decrease in infiltrability then proceeds slowly in all cases, and the final infiltrability ranking is: wet AL > dry - L = wet - AL > dry - L. The porosity of the crust was analysed using mercury porosimetry, bulk volume measurements and the volumetric water contents at the pressure potentials ranging from -0.1 to -10 m. The crust porosity analysis shows that a structural porosity exists within the crusts. Three hypothesis are made to explain the final infiltrability order: interconnected structural pores perform the water transfer under rain (AL - wet); air can be caught in structural pores due to desaturation between subsequents rains (dry - AL); or structural pores remain saturated but are not interconnected (dry - L and wet - L).