Relationships between soil water content, evapotranspiration, and irrigation measurements in a California drip-irrigated Pinot noir vineyard

Authors: Wilson, Tiffany; Kustas, William - Bill; Alfieri, Joseph; Anderson, Martha; Prueger, John; McKee, Lynn; ALSINA, M. - E & J Gallo Winery; SANCHEZ, L. - E & J Gallo Winery; ALSTED, K. - Uc Davis Medical Center

Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/2020
Publication Date: 4/30/2020
Citation: Wilson, T.G., Kustas, W.P., Alfieri, J.G., Anderson, M.C., Prueger, J.H., McKee, L.G., Alsina, M., Sanchez, L., Alsted, K. 2020. Relationships between soil water content, evapotranspiration, and irrigation measurements in a California drip-irrigated Pinot noir vineyard. Agricultural Water Management. https://doi.org/10.1016/j.agwat.2020.106186.
DOI: https://doi.org/10.1016/j.agwat.2020.106186

Interpretive Summary: The Central Valley of California relies on irrigation for crop production, but water resources, particularly groundwater, have reached critical stages due to extended drought periods and overuse by irrigated agriculture. To improve efficiency in vineyard irrigation requires an understanding of the relationships between root zone soil water content (SWC) and vine water use or evapotranspiration (ET). Field measurements of SWC and ET in two adjacent Pinot noir vineyards near Lodi, CA from 2013 to 2017 were analyzed. Interactions between the root zone and evaporative demand change throughout the growing season. Consequently, key to understanding vineyard water status using relatively shallow SWC observations is to use them in conjunction with ET data. For example, delaying the initiation of irrigation until a clear relationship between SWC and ET emerges may both reduce the total amount of water used and give the grower more control over vine growth and grape quality affected by water status.

Technical Abstract: The Central Valley of California relies on irrigation for crop production, but water resources, particularly groundwater, have reached critical stages due to extended drought periods and overuse by irrigated agriculture. The purpose of the Grape Remote sensing Atmospheric Profile and Evapotranspiration eXperiment (GRAPEX) project is to improve efficiency in vineyard irrigation through field measurements and modeling efforts using remote sensing. In this study, we analyze multi-year timeseries of ground-based soil moisture and evapotranspiration (ET) measurements collected during GRAPEX to identify patterns that may inform future irrigation recommendations based on remotely sensed ET. The study focuses on field data collected in two adjacent Pinot noir vineyards near Lodi, CA from 2013 to 2017. The data used for this analysis are reference evapotranspiration (ETref), actual evapotranspiration (ETa), mean daytime soil water content (SWC) measured down to 90 cm, precipitation, and irrigation. The relationship between SWC and the ratio of ETa/ETref (used as a soil moisture proxy indicator) changes throughout the spring and summer months due to advancing phenological stages and management practices. In early spring, when the interrow cover crop is the primary source of ET, ETa is strongly correlated with SWC. As the vine canopy grows in, the strong correlation breaks down as the vines begin to access to water beyond the depth of the soil moisture sensors. As the soil profile dries out during the summer, the correlation between ETa and SWC once again emerges as the vines become strongly dependent on irrigation. The dynamic interaction between the upper and lower root zone profile and evaporative demand means that the key to understanding vineyard water status using relatively shallow SWC observations is to use them in conjunction with ETa data. For example, delaying the initiation of irrigation until a clear relationship between SWC and ETa emerges may both reduce the total amount of water used and give the grower more control over vine growth and grape quality affected by water status.