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 0.64 mm and 1.83 mm, and between 0.69 mm and 2.52 mm 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.

Soil evaporation is a significant unproductive loss of water that needs to be and can be managed in irrigated systems. A method is used to estimate soil evaporation based upon soil surface temperature change between a saturated and drying soil. The relative evaporation (RE) method of Ben-Asher et al. (1983) was deployed. Soil surface temperature in a drip irrigated vineyard was collected using infra-red temperature sensors. Average daily soil evaporation under-vine was between 0.6mm and 1.8mm and between 0.7mm and 2.5mm for the inter-row. Evaporation from the soil is an important part of the water balance of a crop (Burt et al. 2005). Previous estimates vary widely, from 30-65% of evapotranspiration (Kerridge et al 2008a). The Ben-Asher et al. (1983) method allows potential soil evaporation to be estimated from the daily latent fluxes of a saturated, steady-state dry and a drying soil. By calculating a relative evaporation (RE) factor and multiplying it by an estimate of potential evaporation, determined for example by the FAO-56 procedure (Allen et al., 1998), an estimate of soil evaporation may be made. The main benefit of this method is that it allows rapid and simultaneous estimates of evaporative flux to be measured at numerous sites under study. This can then be linked with methods for spatial estimation of plant water use and stress (Hornbuckle et al., 2008b).