Using soil surface temperature to assess soil evaporation in a drip irrigated vineyard

Evaporation from the soil is an important part of the water balance of a crop, when considering water use efficiency. In this paper, a non-intensive method is tested to estimate relative soil evaporation, which is based upon a linear function of soil surface temperature change between a saturated and drying soil. The relative evaporation (RE) method of Ben-Asher et al. (1983) was calibrated using microlysimeters and thermal imaging. Soil surface temperature in a drip irrigated vineyard was then collected using infrared temperature sensors mounted on a quad bike, on several days of the 2009–2010 season. Soil surface temperature in the vineyard ranged from 4.6°C to 65.5°C undervine and 6.8°C to 75.6°C in the middle of the row. The difference between daily minima and maxima of soil surface temperature ranged from 20.2°C to 59.7°C in the inter-row and 13.6°C to 36.4°C undervine. Relative evaporation averaged 54% of evaporation from a saturated soil in the inter-row and 97% undervine. Based upon the calculation of RE, the average daily amount of soil evaporation undervine was between 0.64mm and 1.83mm, and between 0.69mm and 2.52mm inter-row. The soil evaporation undervine and inter-row both exhibited spatial variability across the vineyard, however the undervine area had less spatial variability compared to the inter-row area.