AUTHOR=Padilla Francisco M. , de Souza Romina , Peña-Fleitas M. Teresa , Gallardo Marisa , Giménez Carmen , Thompson Rodney B. 

TITLE=Different Responses of Various Chlorophyll Meters to Increasing Nitrogen Supply in Sweet Pepper

JOURNAL=Frontiers in Plant Science

VOLUME=Volume 9 - 2018

YEAR=2018

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2018.01752

DOI=10.3389/fpls.2018.01752

ISSN=1664-462X

ABSTRACT=<p>Intensive vegetable production is commonly associated with excessive nitrogen (N) fertilization and associated environmental problems. Monitoring of crop N status can enhance crop N management. Chlorophyll meters (CMs) could be used to monitor crop N status because leaf chlorophyll (chl) content is strongly related to crop N status. To monitor crop N status, relationships between CM measurements and leaf chl content require evaluation, particularly when excessive N is supplied. The SPAD-502 meter, atLEAF+ sensor, MC-100 Chlorophyll Concentration Meter, and Multiplex sensor were evaluated in sweet pepper with different N supply, throughout the crop, ranging from very deficient to very excessive. CM measurements of all sensors and indices were strongly and positively related to leaf chlorophyll <italic>a</italic> + <italic>b</italic> content with curvilinear relationships over the entire range of chl measured (∼0–80 μg cm<sup>-2</sup>). Measurements with the SPAD-502, and atLEAF+, and of the Multiplex’s simple fluorescence ratio index (SFR) had asymptotic responses to increasing leaf chl. In contrast, the MC-100’s chlorophyll content index (CCI) had a progressively increasing response. At higher chlorophyll <italic>a</italic> + <italic>b</italic> contents (e.g., &gt;40 μg cm<sup>-2</sup>), SPAD-502, atLEAF+ and SFR measurements tended to saturate, which did not occur with CCI. Leaf chl content was most accurately estimated by CCI (<italic>R</italic><sup>2</sup> = 0.87), followed by the SPAD-502 meter (<italic>R</italic><sup>2</sup> = 0.85). The atLEAF+ sensor was the least accurate (<italic>R</italic><sup>2</sup> = 0.76). For leaf chl estimation, CCI measured with the MC-100 meter was the most effective of the four sensors examined because it: (1) most accurately estimated leaf chl content, and (2) had no saturation response at higher leaf chl content. For non-saturating leaf chl content (∼0–40 μg cm<sup>-2</sup>), all indices were sensitive indicators. As excessive applications of N are frequent in intensive vegetable crop production, the capacity of measuring high leaf chl contents without a saturation response is an important consideration for the practical use of chlorophyll meters.</p>