Variation of hydraulic conductivity in a tilled soil

Summary Tillage increases the spatial variation of the structure and saturated hydraulic conductivity of the soil. Recent advances have related morphological macroscopic features of the structure to the cultivation operations responsible for compaction, fragmentation and displacement of the soil. This description is based on a compartmentation of the tilled soil, vertically (seed bed, ploughed layer, and untilled soil) and horizontally (below wheel tracks, between wheel tracks). Between the wheel tracks we distinguished structures according to the type of macroporosity within clods. We measured infiltration using tension infiltrometers in the different compartments of a soil profile in an experimental plot on a silt loamy Calcic Cambisol of the Parisian Basin. Hydraulic conductivity in the seed bed was on average among all potentials six times greater than that of the ploughed layer and twice as large as that of the untilled layer. Hydraulic conductivity in the ploughed layer was one third that of the untilled layer. Soil below the wheel tracks had a hydraulic conductivity only 40% of that of the soil between the wheel tracks in the ploughed layer. Between the wheel tracks, the compacted Δ clods had hydraulic conductivities one ninth of that of the macroporous Γ clods. Φ clods, stemming from Δ clods with incipient cracks due to weather effects, had intermediate hydraulic conductivities. These results suggest that a morphological description of the structure of tilled soil will be valuable for a better understanding of the variation of the hydraulic conductivity within tilled soils. Variation de la conductivité hydraulique dans un sol cultivé Résumé Les pratiques culturales engendrent une forte variation spatiale de la structure du sol ainsi que de la conductivité hydraulique à saturation. Ceci est particulièrement vrai lorsque la préparation du sol comporte un labour. Des études récentes ont permis de relier la morphologie de la structure des horizons travaillés décrite à l'échelle macroscopique aux opérations culturales responsables de la compaction, de la fragmentation et du déplacement du sol. La structure d'un sol limoneux labouré du Bassin Parisien a été caractérisée, à partir d'une face d'observation perpendiculaire au sens d'avancement des outils, à l'aide d'une compartimentation distinguant les horizons (lit de semence, horizon labouré sous‐jacent, horizon non‐travaillé) et les parties du profil roulées et non‐roulées. Dans le compartiment labouré