Use of environmental isotopes for field study of water infiltration in the ploughed soil layer

Abstract

The aim of this work was to analyse the influence of soil structure on water movement in different ploughed soil layers. The structure of soil 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: clods showing a very low macroporosity (called Δ clods) and clods showing high macroporosity (called Γ clods). Results show: (i) equivalent mean volumetric water contents for the different soil profiles and bulk differences between the types of clods: Γ clods have a lower and less variable water content than the Δ ones; (ii) different oxygen-18 amounts between the two types of clods and between the different profiles which reveal a difference in water movement in the two types of clods for the three studied ploughed layers, thus (iii) when the 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 clods according to a theoretical scheme of infiltration is therefore determined. These results emphasize the heterogeneity of water movement in the ploughed soil layer and quantify it. Consequences on sampling scheme of soil solution for environmental purposes and modelisation of water movement are emphasized.