Chlorophyll Meter Calibrations for Chlorophyll Content Using Measured and Simulated Leaf Transmittances

Abstract

Konica-Minolta SPAD-502 leaf chlorophyll meters provide a relative value of leaf chlorophyll content, and from the literature, there are considerable variations among the calibration equations between total chlorophyll contents (mg chlorophyll a + b cm -2 ) and SPAD-502 values. Our objective was to determine the leaf properties that contributed to the variations in calibration. We determined the internal calibration coe cient of ve SPAD-502 meters so that leaf transmittances in the red (650 nm) and near-infrared (940 nm) could be used to calculate SPAD-502 values. A leaf optics model, PROSPECT, was used to simulate transmittances and the chlorophyll-SPAD-502 relationship for di erent leaf optical properties. Spectral and leaf data from maize (Zea mays L.) showed that PROSPECT predicted leaf transmittances within 2%. Maize leaf data used in the PROSPECT model predicted the relationship between chlorophyll content and the SPAD-502 value, although a polynomial regression was a better t to the data. ere was a physical interaction between chlorophyll content and optical leaf structure a ecting leaf transmittances, which is not in the equation for calculating SPAD-502 values. Changing the PROSPECT leaf structure parameter resulted in di erent chlorophyll-SPAD-502 meter relationships, which were similar to the measured range of variation from calibration equations found in the literature. If the red and near-infrared transmittances are saved for each chlorophyll meter reading, then leaf radiative transfer models such as PROSPECT may be inverted to determine the actual leaf chlorophyll content. . Th e USDA is an equal opportunity provider and employer. Mention of trade names does not imply endorsement by the USDA.

Assessment of Portable Chlorophyll Meters for Measuring Crop Leaf Chlorophyll Concentration

“…Light transmittances at wavelengths centered at 940, 931, 850, 710, 653, and 650 nm were then simulated. The spectral response functions of the LEDs used in the PCMs [50][51][52] were also considered. A global sensitivity analysis (GSA) was conducted to determine the contribution variation for each leaf parameter, using the SIMLAB (Simulation Environment for Sensitivity and Uncertainty Analysis, http://simlab.jrc.ec.europa.eu/) software.…”

Assessment of crop foliar nitrogen using a novel dual-wavelength laser system and implications for conducting laser-based plant physiology

“…After clipping the SPAD meter to the surface of the leaf, the instrument measures the transmittance of red (650 nm) and near infrared (950 nm) light through the leaf. Based on the two transmittance values, a relative chlorophyll index value was calculated which has shown to be closely correlated to foliar chlorophyll and N concentration (e.g., Schepers et al, 1992;Fox et al, 1994;Richardson et al, 2002;Hunt and Daughtry, 2014). Flag leaf N estimates were obtained in the laboratory by using an automated dry combustion instrument (TruSpec CN, Leco Corporation, St. Joseph, MI).…”

Effects of nitrogen application rates on the spatio-temporal variation of leaf SPAD readings on the maize canopy

“…An SPAD-502 chlorophyll meter (Minolta, 1989; Raymond Hunt and Craig, 2014; Yuan et al ., 2016 a ; Borhan et al ., 2017) is a rapid, non-destructive, hand-held spectral device that is widely used for leaf chlorophyll measurement in the laboratory and in the field (Li et al ., 2009; Ling et al ., 2011; Xiong et al ., 2015; Yuan et al ., 2016 b ). SPAD readings can be used to quantify leaf nutrient content and reflect leaf functional status (Wang et al ., 2018; Yang et al ., 2018; Li et al ., 2019).…”