Using Mass Balance to Determine Plant Water Status of Individual Grape Vines
Shayla Nikzad, Jean-Jacques Lambert, Zibran
Chaus, Christopher Parry, Andrew McElrone, Andre Knoesen, and
David Block*
*University of California at Davis, One Shields Avenue, Davis, CA
95616 (deblock@ucdavis.edu)
Bulk irrigation is the status quo in vineyards. However, even
when comparing vines planted side by side, irrigation needs may
vary dramatically. Additionally, berry quality may be improved by
decreasing this heterogeneity between vines. For these reasons,
along with the increasing scarcity of water resources in
California grapegrowing regions, there is a need to increase the
resolution of vineyard irrigation. However, traditional methods
of measuring plant water stress (i.e., pressure bomb, porometry,
and soil moisture sensing) pose major complications when applied
to individual vines. This manifests itself either in the
inability of these methods to function at such a high resolution,
or in the labor-intensive nature of taking single-vine
measurements. Our work focuses on detecting the
evapotranspiration rate of individual grapevines using a mass
balance approach. Four individually potted vines were placed on
load cells. Each vine was outfitted with four humidity sensors
and a single anemometer. Two of the four vines were watered
with
48 kg of water, while the remaining two vines were watered with
36kg of water only, every ten days to simulate variable water
stress. From budbreak, the relative humidity, wind speed through
the canopy, and mass of each potted vine were re-corded
continuously. Estimated values of evapotranspiration were
calculated from a mass balance using the vine canopy as a control
volume. These estimated values were compared to the absolute
measurement of lost water mass recorded by the load cell.
Additionally, the mass balance estimates were compared to
continuous soil moisture measurements and porometric and pressure
bomb data taken once and twice a day, respectively. This work is
a continuation of a similar experiment conducted on a single
vine, in which evapotranspiration rates calculated via mass
balance showed agreement with the evapotranspiration rates from
the load cell.
Funding Support: Cypress Semiconductor, Ernest Gallo Endowed Chair in Viticulture, and Till Guldimann
