%0 Figure %A M. Padilla, Francisco %A de Souza, Romina %A Peña-Fleitas, M. Teresa %A Gallardo, Marisa %A Giménez, Carmen %A Thompson, Rodney B. %D 2018 %T Image_2_Different Responses of Various Chlorophyll Meters to Increasing Nitrogen Supply in Sweet Pepper.pdf %U https://frontiersin.figshare.com/articles/figure/Image_2_Different_Responses_of_Various_Chlorophyll_Meters_to_Increasing_Nitrogen_Supply_in_Sweet_Pepper_pdf/7387334 %R 10.3389/fpls.2018.01752.s002 %2 https://frontiersin.figshare.com/ndownloader/files/13663412 %K Capsicum annuum %K fluorescence %K fertilization %K optical sensors %K transmittance %X

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 a + b content with curvilinear relationships over the entire range of chl measured (∼0–80 μg cm-2). 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 a + b contents (e.g., >40 μg cm-2), SPAD-502, atLEAF+ and SFR measurements tended to saturate, which did not occur with CCI. Leaf chl content was most accurately estimated by CCI (R2 = 0.87), followed by the SPAD-502 meter (R2 = 0.85). The atLEAF+ sensor was the least accurate (R2 = 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-2), 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.

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