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RESEARCH PRODUCT

Effect of cultivation techniques on the hydrodynamic and mechanical behaviour of the "Lauragais-terreforts"

subject

description

The effect of various seed bed preparations on hydrodynamic and mechanical parameters was studied experimentally by simulated rainfall on clayeyloamy soils Lauragais, which had developed on chalky molasse on a slope greater than 12 %. The level of soaked up rain ("pluie d'imbibition", Pi) is closely connected to the inital degree of saturation of the soil ; it varies from 10 to 24 mm when the soil is humid and increases when the soil is dry (14 to 47 mm). But when the soil surface is crusted the Pi is less and seems to be no longer controlled by the degree of water in the soil. Treatments with fine structural elements show the fewest possibilities of infiltration during the soaking up stage ; thickening the seed bed does not appear to have any effect on Pi. The double packing down of the soil poses a real obstacle to infiltration. The susceptibility to runoff is all the greater as the percentage of clods less than 0.5 cm is high. Runoff is reduced when the soil is dry and increases sharply with the intensity of the rain and superficial crusting. The intensity of infiltration permanent regime (FN) seems better on the treatments with fairly large structural elements (from 6 to 17 mm. h-1). The thickening of the seed bed did not improve FN (from 5 to 11 mm h-1). On the other hand, the double thickening of the soil is a real brake on infiltration (1 to 5 mm h-1). The intensity of infiltration permanent regime drops when the intensity of the rain increases. The average solid load is very variable, probably on account of the many "lachages" of micro-structures. It is high for the treatments with fine structural elements if the soil is dry (24 to 27 g L-1) and especially if the soil is humid (19 to 41 g. L-1) The average solid load is less on treatments with fairly large structures (1 to 2 g. L-l). It increases sharply with the slope and appears to be independent of rainfall intensity. Treatments with fine structural elements are characterized by high solid outflows (200 to 300 g.m2 h-1). They increase sharply with rainfall intensity and the slope and drop with a low level of soil saturation.