Infiltration et problèmes agronomiques quelques approches expérimentales

Ing. Agri.-Dr Ing., Maître de Recherches I.N.R.A.

Résumé

The agronomist has to deal with the problem of water infiltration into the ground whenever he is faced with such tasks as soil conservancy, optimum land preparation control, meeting plant water requirements and protecting plants against excess of water. A few examples of the experimental approach to the problem are described, which are designed to provide a better understanding of the phenomena involved and to enable the effect of the various factors all appearing at the same time to be evaluated. The first part of the article gives the results obtained in infiltration tests with dry soil columns. The effect of rain fall intensity on soil filling rate is demonstrated and attention is drawn to an equation relating front progression rate to intensity, the coefficients of which express the intrinsic properties of the ground. The second part of the article deals with vertical water redistribution. A series of laboratory and field experiments show that two distinct regimes exist, one slow and the other fast. A critical moisture value-soil retention capacity-marks the transition from one regime to the other, but some doubt is expressed as to its meaning. The effect of the amount of water applied on how redistribution of the water in the ground takes place is emphasised and an equation allowing for the interaction of various parameters on this phenomenon is put forward. A new device designed for the study of rain water infiltration into a field is described in the third part of the article, which also involves the measurement or recording of water tension. The results obtained provide a check on the deficit concept (i.e. on retention capacity) and enable the respective proportions of the water supplied by a fall of rain taken up by the ground and infiltrating down to the aquifer to be determined and the rate of transfer and soil filling rate with water in motion to be calculated.