USE OF ENVIRONMENTAL ISOTOPES FOR FIELD-STUDY OF WATER INFILTRATION IN THE PLOWED SOIL LAYER

The aim of this work was to analyse the influence of soil structure on water movement in different ploughed soil layers, The structure of so il layers was accurately defined and described. The water content and the oxygen-18 content of the water, taken as an environmental tracer, were measured taking into account the internal structure of clods: clo ds showing a very low macroporosity (called Delta clods) and clods sho wing high macroporosity (called Gamma clods). Results show: (i) equiva lent mean volumetric water contents for the different soil profiles an d bulk differences between the types of clods: Gamma clods have a lowe r and less variable water content than the Delta ones; (ii) different oxygen-18 amounts between the two types of clods and between the diffe rent profiles which reveal a difference in water movement in the two t ypes of clods for the three studied ploughed layers, thus (iii) when t he relative abundance of each type of clods in the different profiles is taken into account, the patterns of water movement in each profile can be related to its own organization, The relative isolation of clod s according to a theoretical scheme of infiltration is therefore deter mined, These results emphasize the heterogeneity of water movement in the ploughed soil layer and quantify it, Consequences on sampling sche me of soil solution for environmental purposes and modelisation of wat er movement are emphasized.