Soil Water Flow Evaluation at Top, Middle and Bottom Position at the Vineyard Hillslope

In the soil vadose zone, one of the critical processes is the water flow which is important for the root uptake but could also enhance transport of potentially harmful agricultural substances to surface and groundwater. Thus, we established the first Croatian critical zone observatory SUPREHILL to specify subsurface preferential flow and nonlinear agrochemical transport processes. Among other instruments, wick lysimeters were installed at the 40 cm depth at the top, middle, and bottom of the vineyard hillslope. The water volumes collected in lysimeters were measured every two weeks. For estimation of soil hydraulic properties (SHP) using HYPROP and WP4C techniques, the undisturbed soil cores (250 cm3) were taken from the same positions at 1520 and 3540 cm depth in three repetitions. The first results from one-year research showed the highest amount of water collected in lysimeters at the hilltop and the lowest at the middle part of the hillslope. Estimated SHP showed that the middle position mostly has the highest values of bulk density and the lowest values of porosity which could cause slower vertical water movement. Furthermore, the water volume in lysimeters could be a result of variable slope in the investigated hillslope. For example, the slope on the top is minor compared to the middle and the bottom thus resulting in the slowest lateral subsurface flow and the highest amount of collected water. The middle and the bottom have similar slopes, but below the bottom position, the slope becomes less steep affecting the water movement at that position and reducing lateral subsurface flow causing a higher amount of water compared to the middle part. At the middle position, the subsurface runoff is possibly the main water pathway since the middle part has a steep slope that continues to the bottom of the hillslope. Thus, to precisely determine water movement at vineyard hillslope and therefore the agrochemical transport, later in research we will combine results obtained by sensors set at the field at various depths, undisturbed soil columns experiments, CT-scanning, and numerical simulations.