Grass intercrop and soil water content have a secondary effect on soil heat flux (SHF) in a wine vineyard – implications on SHF measurements

Authors: AGAM, N. - Ben Gurion University Of Negev; Kustas, William - Bill; Alfieri, Joseph; Gao, Feng; McKee, Lynn; Prueger, John; HIPPS, L.E. - Utah State University

Submitted to: Irrigation Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/3/2019
Publication Date: 5/7/2019
Citation: Agam, N., Kustas, W.P., Alfieri, J.G., Gao, F.N., Mckee, L.G., Prueger, J.H., Hipps, L. 2019. Grass intercrop and soil water content have a secondary effect on soil heat flux (SHF) in a wine vineyard – implications on SHF measurements. Irrigation Science. https://doi.org/10.1007/s00271-019-00634-6.
DOI: https://doi.org/10.1007/s00271-019-00634-6

Interpretive Summary: In vineyards, soil heat flux accounts for as much as 30% of net radiation. Therefore, inaccurate estimates of soil heat flux may lead to meaningful errors when quantifying the surface energy balance and evapotranspiration (ET) from tower-based measurements used for model validation. Due to the natural variability of soils and the micro-environmental variability in vineyards, it is a challenge to measure a representative soil heat flux necessitating multiple measurements per site. A field study deployed an 11-sensor array to obtain a representative value of area-averaged soil heat flux in two vineyards located in the Central Valley of California. The variability of incoming solar radiation was found to be the primary source for the heterogeneous soil heat flux distribution in July, while in March a more uniform distribution of soil heat flux was observed. The water content distribution and the grass cover in the interrow seem to have played only a secondary role in the spatial and temporal variation in soil heat flux. It was further found that a transect of 5 equally distributed sensors across the interrow accurately represented the area-averaged soil heat flux given by the 11-sensor array, particularly during the growing season. Thus, a transect of 5 sensors provides reliable area-averaged soil heat flux needed for surface energy balance measurements. These findings are very useful in designing surface energy balance/ET tower measurement systems deployed for model validation in vineyard landscapes.

Technical Abstract: In vineyards, soil heat flux accounts for as much as 30% of net radiation. Therefore, inaccurate estimates of soil heat flux may lead to meaningful errors when quantifying the surface energy balance and evapotranspiration (ET) from tower-based measurements used for model validation. Due to the natural variability of soils and the micro-environmental variability in vineyards, it is a challenge to measure a representative soil heat flux necessitating multiple measurements per site. A field study deployed an 11-sensor array to obtain a representative value of area-averaged soil heat flux in two vineyards located in the Central Valley of California. The variability of incoming solar radiation was found to be the primary source for the heterogeneous soil heat flux distribution in July, while in March a more uniform distribution of soil heat flux was observed. The water content distribution and the grass cover in the interrow seem to have played only a secondary role in the spatial and temporal variation in soil heat flux. It was further found that a transect of 5 equally distributed sensors across the interrow accurately represented the area-averaged soil heat flux given by the 11-sensor array, particularly during the growing season. Thus, a transect of 5 sensors provides reliable area-averaged soil heat flux needed for surface energy balance measurements. These findings are very useful in designing surface energy balance/ET tower measurement systems deployed for model validation in vineyard landscapes.