Rapid non‐destructive assessment of leaf water status with low‐cost transmittance meters

Tools for more efficiently managing agricultural production and the use of limited water resources are required in the context of a growing global population, while the increasing threat posed by droughts and wildfires necessitates improved methods for risk assessment, forecasting and early warning.

Quantifying leaf water content is central to these challenges. However, traditional gravimetric measurements are labour‐intensive and time‐consuming, limiting the assessment of spatial variation, and are not appropriate for all environments due to their destructive nature. We investigate low‐cost transmittance meters for rapid non‐destructive assessment of leaf water status, making use of radiative transfer simulations and dehydration experiments to test their theoretical and real‐world sensitivity to leaf water content.

Radiative transfer simulations demonstrate that a transmittance‐based meter operating at 940 and 1450 nm is ideally suited to the assessment of leaf water status. Dehydration experiment results reveal strong relationships between the logarithm of the ratio of transmittance at 940 and 1450 nm (as measured with a low‐cost transmittance meter) and both equivalent water thickness ( r ²  ≥ 0.85) and fuel moisture content ( r ²  ≥ 0.81).

Our results highlight the potential of low‐cost transmittance meters, assembled using inexpensive and readily available components, for rapid non‐destructive assessment of leaf water status. Such meters have strong potential to provide valuable information on crop water availability and wildfire risk.