A novel low-cost trunk load cell sensor for estimating canopy transpiration in the grapevine

Reliable, uninterrupted, and affordable measurements of vine water status continue to be a challenge within a global warming scenario. While recent work has concentrated on micro-tensiometers able to provide a continuous recording of trunk water potential, the current study provides the first calibration of a newly designed, low-cost load cell weight (LCW) transducer applied to the vine trunk, yielding an electric output in mV. The calibration run was conducted for 47 days (24 August–9 October 2022) on six mature field-grown and well-watered Cabernet Sauvignon vines enclosed in plastic chambers for uninterrupted monitoring of whole-vine transpiration (Ttotal). To broaden the range of Ttotal values, half of the vines were trimmed at flowering at eight main leaves. Correlations between the average daily Ttotal and maximum daily LCW difference for data pooled over the whole measuring period were considerably loose, with or without the inclusion of rainy or overcast days. Conversely, correlations between mean Ttotal and LCW the latter given as the diurnal maximum minus the instantaneous reading run from dawn to about 5 pm over 27 mostly clear days gave a very close fit (R2 = 0.95–0.97) in both canopy treatments. Likewise, the same regressions run on data averaged over four mostly cloudy days maintained a similar accuracy (R2 = 0.93–0.94) of the interpolated linear models. Once referred to data taken diurnally on either mostly clear or mostly cloudy days between sunrise and maximum Ttotal reached around 5 pm, the LCW sensor showed high accuracy. Moreover, the sensors were sensitive enough to detect differences induced by a variation in canopy size due to early shoot trimming. Its very low cost (around 12 euros), easy and fully non-invasive installment and negligible maintenance requirements encourage deeper evaluation in terms of sensitivity to phenology, cultivar and water supply levels.