Controlling a subsurface drip irrigation system based on soil water monitoring is a very efficient way to supply grapevines with water for optimal thriving and high vintage quality. However, finding an adequate location for sensor installation is a great challenge due to the well-known spatio-temporal variability of soil moisture and possible measurement uncertainties. The variations depend on soil structure, soil hydraulic properties, or plant water uptake, for instance. Subsequently, these factors are influenced by management practices such as soil cultivation or cover cropping. The main objective of this study was to gain experience in order to give recommendations for soil water monitoring in a vineyard in accordance to local management practices. Soil moisture was surveyed across a study plot in a vineyard. A gouge auger was used to obtain soil samples from both sides of two vine rows for determining gravimetric water content. Volumetric soil water content was measured near the vine rows by inserting a portable soil water probe into pre-installed access tubes. Soil water variability was investigated under rain-fed conditions, and before and after a subsurface drip irrigation event. Differences were considered between inter-rows that were frequently tilled and those with permanent crop cover. In the first of two study years the variability of soil water content was small as the soil characteristics were relatively homogeneous across the plot and the atmospheric conditions were rather wet. In the second year the deviations were greater due to the more dynamic outer conditions. The alternating cultivation of every second inter-row had a substantial effect on soil water distribution in both years. Representative monitoring across the entire plot should thus consider all inter-rows with distinct cultivation. However, a more efficient procedure is recommended as a basis for irrigation control, considering the uncertainties caused by spatial variability.
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