Characterization and modelling of water flow on vineyard soil. Effect of compaction and grass cover

In the Burgundy vineyard, frequent tractor traffic and management of inter-rows alternating grass cover and chemical weed-control lead to structural soil contrast between row and inter-row. The aim of this study was to characterize and model water flow in relation with topsoil structure modifications induced by these practices. Void ratio of the different soil volumes were determined using bulk density measurements. Water flow was measured with tensiometers under two simulated rainfalls. Hydraulics properties of soil volumes defined at the profile level was characterized by water retention curve and infiltrometer measurements. Hydrus 2D software was used for 2D modelling of water flow on a transect perpendicular to the rows. Compaction of the 25 first centimetres of inter-row topsoil was observed in the two types of interrows. It led to a void ratio reduction of 37% and a reduction of the saturated hydraulic conductivity generating less infiltration than in rows. Grass-covered inter-rows were characterized by a macroporous mat root at the soil surface (0-3 cm) in the upper part of the underlying compacted volume. More infiltration was measured in inter-rows with grass cover than in chemically weed-controlled inter-rows. Modelling fairly reproduced contrast of water flow contrast in relation with soil structure for the first 25 centimetres. However, modelling was unable to reproduce flow in volume likely to be affected by preferential flow. Between 25 and 70 centimetres depth, soils containing numerous vine roots would be the seat of preferential flow pathways distributing water laterally from rows to inter-rows. Effectiveness of preferential pathways would increase with soil moisture and rainfall intensity.