Measurement and estimation of leaf area index (LAI) using commercial instruments and smartphone-based systems

Abstract

The experimentation carried out within this project aimed at comparing various methods used to estimate leaf area index (LAI), which is a key variable to describe the vigour and productive potential of a crop. The direct or "destructive" method requires the removal of the biomass of the sample and is a very laborious and burdensome technique. The indirect estimates consist in the acquisition of a series of readings taken directly in the field with specific instruments, mainly based on the measurement of the quantity of light intercepted by the foliage and on the use of complex mathematical models. Indirect methods allow for a quick estimation of the LAI and there is a strong interest in developing economic and user-friendly tools. The tools compared in the present study included two state-of-the-art, rather expensive, commercial instruments, i.e. the Sunscan ceptometer (Delta-T, UK) and the LAI-2000 (Li-Cor, USA). These were compared to inexpensive alternatives offered by hemispheric photography from a smartphone equipped with a fish-eye lens and from a smartphone app called "Pocket LAI". All the methods tested showed the ability to provide an effective estimate of the LAI even if sometimes with an underestimation of the value measured by the direct method.