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

Francisco M Padilla,M Teresa Peña-Fleitas,Romina De Souza,Rodney B Thompson,Marisa Gallardo,Carmen Giménez

doi:10.3389/fpls.2018.01752

Francisco M Padilla, M Teresa Peña-Fleitas + Show 4 more

Open Access

https://doi.org/10.3389/fpls.2018.01752

Copy DOI

Abstract

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.

Highlights

Optimal crop nitrogen (N) management requires that the amount and timing of the N supply be matched to crop demand (Meisinger et al, 2008; Gebbers and Adamchuk, 2010; Ata-UlKarim et al, 2016)
The best fit equations to estimate chlorophyll a + b content from chlorophyll meter (CM) measurements are presented in Table 2; those for the separate estimation of chlorophyll a and chlorophyll b contents are presented in Supplementary Table S1
The results suggest that chlorophyll fluorescence (ChlF)-based indices such as SFR_R and SFR_G, measured by the Multiplex, have no clear advantage, in terms of sensitivity or the relationship with leaf chl, compared to transmittance-based measurements made with the MC-100 meter and the SPAD-502 meter

Summary

Introduction

Optimal crop nitrogen (N) management requires that the amount and timing of the N supply be matched to crop demand (Meisinger et al, 2008; Gebbers and Adamchuk, 2010; Ata-UlKarim et al, 2016). Some optical sensors provide relative measurements of compounds that are sensitive to crop N amount (Fox and Walthall, 2008; Samborski et al, 2009; Tremblay et al, 2012; Padilla et al, 2018). All CMs determine the relative chl content per leaf surface area; the measured value is a dimensionless value that strongly relates to the actual amount of chl (Monje and Bugbee, 1992; Markwell et al, 1995; Parry et al, 2014)

Objectives

Methods

Results

Discussion

Conclusion