Smartphone tools for measuring vine water status

Abstract

Smartphones have several advantages over specialist systems for extending crop monitoring technology to small to medium scale horticultural operators, including ubiquity, price, user familiarity and the ease of implementing updates. They also contain sufficient computing power that analysis and support software can be contained within the phone. This work evaluated a range of smartphone based tools for measuring vine water status, leading to the development of the most promising tool into a smart phone application that can be easily used by vineyard managers. Potential systems evaluated included: 1) an infrared camera that is integrated into or connected directly to the smartphone and uses established techniques for the analysis of thermal imagery to assess water status; 2) a portable near infra-red spectrophotometer that interfaces with the phone and measures reflectance across wavelengths for the calculation of water status indices; 3) a 3D camera that is integrated into or connected to the phone via WiFi and can use image analysis to assess the shape or orientation of the leaves; 4) a microscope attached to the smartphone camera or as a separate portable unit that can be used to measure stomatal number and aperture and then calculate stomatal conductance. A trial site with a range of irrigation deficit treatments applied to 'Chardonnay' and 'Cabernet Sauvignon' grapevines was established in the Riverland of South Australia. Water status measurements from the smartphone based sensors described above were benchmarked against conventional methods including mid-day stem water potential and stomatal conductance. The thermal infrared camera system was selected as the most accurate and robust option for development into an app, which will be released to selected viticulturists for beta testing in 2017.