Below Canopy Evaporation in a Drip-Irrigated Vineyard in Southern Israel.

Separating evapotranspiration (ET) into soil evaporation (E) and canopy transpiration (T) is challenging, but key for crops with precise water requirements and large areas of exposed soil. Wine vineyards are planted in widely spaced rows and require very exact water application to maximize water productivity as well as to enhance fruit quality by allowing moderate levels of stress during certain phenological stages. Evaporation is expected to be a function of soil, climate, irrigation regime, and vine growth stage/canopy development and will therefore change dynamically at both daily and seasonal time scales. The objective of this research was to quantify E in a drip irrigated vineyard under arid conditions with a specific focus on spatial and temporal variations of E along the inter-row.

 An experiment was conducted in an isolated commercial desert vineyard planted in North-South row orientation, with a mean annual precipitation of 90mm. Continuous measurements above the canopy included ET, solar radiation, air temperature and humidity. Short-term intensive measurements below the canopy were conducted at ground level, along transects between adjacent vine rows.  Measurements included actual E using micro-lysimeters, potential E (E_p) with micro-pans, and solar radiation using pyranometers. Results show a clear effect of shading on below canopy E_p, with distinct and different periods of high and low daytime E_p at mid-inter-row, quarter-row and row positions in the rows. The consequences of below canopy observations for whole (vineyard) system water and energy budgets will be highlighted.