Accelerating leaf area measurement using a volumetric approach

Despite the advances in the techniques of indirect estimation of leaf area, the destructive measurement approaches have still remained as the reference and the most accurate methods. However, even utilizing the modern sensors and applications usually requires the laborious and time-consuming practice of unfolding and analyzing the single leaves, separately. In the present study, a volumetric approach was tested to determine the pile leaf area based on the ratio of leaf volume divided by thickness. For this purpose, the suspension technique was used for volumetry, which is based on the simple practice and calculations of the Archimedes principle. The results indicated that the wheat volumetric leaf area (VLA), had an approximately 1:1 correlation with the conventionally measured optical leaf area (OLA). Exclusion of the midrib volume from calculations, did not affect the estimation error (i.e. NRMSE less than 2.61%); however, improved the slope of the linear model by about 6%. The error of sampling for determining the mean leaf thickness of the pile, was also less than 2% throughout the season. Besides, a more practical and facilitated version of the pile volumetry was tested using a Specific Gravity Bench (SGB), which is currently available as a laboratory equipment. As an important observation, which was also expectable according to the 3D shape of the leaf (i.e. expansion in a 2D plane), it was evidenced that the variations in the OLA exactly follows the pattern of the changes in the leaf volume. Accordingly, it was suggested that the relative leaf areas of various experimental treatments may be compared directly based on the volume, and independently of leaf thickness. Furthermore, no considerable difference was observed among the OLAs measured using various image resolutions (NRMSE < 0.212%); which indicates that even the current superfast scanners with low resolutions as 200 dpi may be used for a precision optical measurement of leaf area. It is expected that utilizing the reliable and simple concept of volumetric leaf area, based on which the measurement time may be independent of the sample size, facilitate the laborious practice of leaf area measurement; and consequently, improve the precision of the field experiments.