La Houille Blanche
Number 8, Décembre 1969
|Page(s)||885 - 888|
|Published online||23 March 2010|
Relations entre l'infiltration et les méthodes culturales
Station d'Agronomie, 67, Bd Deltour, 31-Toulouse.
Studies of infiltration have shown that the suction forces developing at the edge of the moist zone are expressed by the conventional Darcy formula if the humectation front is saturated. The hydraulic gradient is then given by : a +x / x + S / x where : a is the depth of water, x is the depth of the saturated medium, S are capillary forces. The importance of the lateral suction forces was shown up in experiments in which media of the same porosity with different-sized pores were placed side by side. The front was found to progress at the same rate in two adjacent media consisting of glass spheres 60 m and 140 m in diameter whereas the rate of progression varied in proportions of 1 to 2 in the fine materials. Saturation of the fine material occurred at all levels from saturated pores in the coarse material. With three adjacent materials the water was found to infiltrate horizontally into the coarse medium and to progress in the form of a curved front in the fine and medium materials, though with a varying fairly considerable lag in the latter case. This pattern also seems likely to apply to water infiltrating into soil made moist by water circulating preferentially in the largest pores. Infiltration and filtration in a given soil of the same porosity were compared for the three following crops. (i) A 20-year old vine growing on bare ground. (ii) Wheat grown after maize. (iii) 3-year old fescue. Infiltration rates were 120 mm/h for the vine, 220 mm/h for the wheat and 3,000 mm/h for the fescue. Filtration rates were 6 mm/h, 10 mm/h and 50 mm/h respectively. These results clearly show the effect of preferential flow paths (probably associated with roots) for both filtration and infiltration, and also the importance of suction forces. Filtration tests carried out with a calcium chloride solution showed only a small part of the porosity to be involved in the flow of water and that the part involved was unaffected by the crops but was closely dependent on the nature of the various soil horizons. These variations in filtration properties have serious consequences for agriculture and cause local temporary waterlogging having a considerable effect on plant behaviour. Owing to their complex make-up the phenomena governing soil infiltration and filtration cannot be investigated solely from a theoretical angle, as it is necessary to also allow for the mechanical characteristics of the water in the medium.
© Société Hydrotechnique de France, 1969