Can we water crops with our phones?:Smartphone technology application to infrared thermography for use in irrigation management

Infrared thermography has been used to assess plant transpiration and infer stress levels in different agricultural production systems. The development of low cost infrared cameras adapted to smart phones provides an opportunity to develop applications that would allow growers to monitor crop water status. We explored the capabilities of this system by assessing the response of crop water stress index (CWSI) to treatments differing in irrigation frequency. Soya bean plants were grown in pots in a glasshouse and different irrigation treatments were applied for two weeks. CWSI, stomatal conductance (gs) and biomass growth were compared in fully irrigated (FI), deficit irrigation (50% ET) applied either at high (HFDI) and low (LFDI) frequency. Statistical differences in CWSI between deficit irrigation and FI treatments were observed when CWSI'0.5. CWSI and gs followed very similar patterns in all treatments, but the higher number of replicates that the thermal camera could measure in a given time and its low variability compared to the porometer increased the capacity to detect differences between treatments. As gs decreased at the end of the experiment in FI plants, probably because of restricted soil volume, differences in CWSI between well-watered and stressed plants diminished, suggesting the need to maintain well-watered plants grown under optimal conditions as a reference baseline. Within the deficit irrigation treatments, CWSI decreased and gs, increased when irrigation was more frequent, but dry biomass and water use efficiency (biomass/irrigation volume) did not change, and were lower and higher than FI plants respectively. These results demonstrate that the low cost thermal camera is suitable to rapidly assess gs, but highlight the issues associated with irrigation scheduling based on this physiological response