1a.Objectives (from AD-416)
Develop an inexpensive method for real-time, remotely-accessible measurement of vineyard-scale evapotranspiration and vine water use.
1b.Approach (from AD-416)
A field based surface renewal system will be used to estimate vine and whole vineyard water use. The work will involve developing a self-calibrated, inexpensive, user-friendly surface renewal system for use in vineyards.
Documents Trust with National Grape & Wine Initiative. Log 40770.
Agreement was established in support of Obj. 3 of the in-house project, the goal being to develop sustainable water management practices for vineyards. The goal of this project is to develop an inexpensive method for real-time, remotely-accessible measurements of vineyard-scale evapotranspiration & vine water use. To improve water-use efficiency in agricultural ecosystems growers need reliable means to estimate real-time crop water demands. Surface renewal is one technique with potential to meet this need, but it must first be appropriately adapted for use in viticultural management. Current surface renewal systems require complicated calibration techniques and data-crunching capabilities. We aim to develop an adaptation of surface renewal techniques suitable for monitoring water use in vineyards through a user-friendly data interface accessible from any device with an internet connection. Once the system is developed and validated, we aim to incorporate these techniques into automated irrigation systems that rely on real-time water use estimates. In 01/2010, a graduate student was hired and began work on the project under the guidance of the PI. Surface renewal(SR) currently requires calibration against other methods in order to obtain accurate measurements of evapotranspiration. The calibration accounts for the linear bias (overestimation or underestimation) of the SR measurements. The calibration factor changes according to the architecture of the crop canopy and the measurement height of the surface renewal sensors. The scientific community has been unable to develop a solution for avoiding the calibration factor that applies to all crop surfaces and measurement heights. Because of the calibration problem, SR, until now, has been limited to research applications. Since 01/2010, the researchers reassessed the original Van Atta model for deriving ramp characteristics from SR thermocouple output. Van Atta proposed the model for a limited range of structure function time lags, but the range was not clearly defined. The power of the model to resolve the coherent structure signals from the random fluctuations has not been quantified well. By re-deriving the original equations and using spectral analysis, the research team successfully accounted for a large portion of the alpha calibration. In other words, correct analysis of the data output allows for much closer estimations of SR relative to Eddy Covariance outputs for various model crop system. The researchers have initiated field experiments to confirm their theoretical analysis and will continue these studies through the Fall 2010. In addition, the team has established field experiments needed to correct the thermal inertia of larger thermocouple sensors. Early results of this work show great potential for converting SR into a readily accessible technique to accurately quantify crop water use in real-time.