Etude experimentale et simulation numerique de l'economie de l'eau sous culture

Abstract

Through a field-scale study of the use of soil water by roots it is possible to specify certain pedo-climatic criteria defining plant behaviour in the “soil—plant—atmosphere” system. The combined use in the field of a NEMO-10 automatic neutron soil moisture meter and tensiometers gives the values of the following parameters: evapotranspiration (ETR), effective root density ( R (z)), hydraulic conductivity of the soil ( K (Hv)) and the effect of increased amounts of water. At the same time the application of a DIFSOL numerical simulation model allows the results to be interpreted and extended to the case of a hysteretic representation of the K (Hv) curve, or to the data on roots activity drawn from the periodic oscillations of the matrix potential. Following a similar laboratory experiment on altered soil columns, the field study pointed out two important differences. 1. (1) With reduced ETR the soil/root competition for water is modified so that the evolution of the water reserves is much more closely related to the hydraulic conductivity of the soil than to the factor of effective root density. 2. (2) Under rainfall or irrigation, simulation of the water profiles observed is possible only if the hysteretic nature of the relation K (Hv) is considered. At 35% Hv, the infiltration and drainage conductivities differ by a factor of 10.