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Yuqi Li and Neil S. Mattson

SPAD readings were measured using a chlorophyll meter (Minolta SPAD-502 chlorophyll meter; Spectrum Technologies, Plainfield, IL). Data are means of six replicates per treatment combination. Petunia flower number was affected by different commercial

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Genhua Niu, Denise S. Rodriguez, and Lissie Aguiniga

damage (acceptable as landscape performance); and 5 = excellent with no foliar damage. Leaf greenness or relative chlorophyll concentration (measured as the optical density, SPAD reading) was recorded at the end of the experiment on three leaves per

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Xiaojie Zhao, Guihong Bi, Richard L. Harkess, Jac J. Varco, Tongyin Li, and Eugene K. Blythe

inflorescences stems and inflorescence stem length), plant height (average height of the three tallest fans), and SPAD reading (SPAD-502; Minolta Camera Co., Japan, one of the first two fully expended leaves was selected to measure SPAD reading) were collected

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Yuqi Li and Neil S. Mattson

, and SPAD were measured. At the end of posttransplanted stage, stem length (from soil to the apical meristem), fresh weight (FW), DW, root index (RI), and SPAD readings were measured. The SPAD readings were quantified using a nondestructive dual

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Tongyin Li, Guihong Bi, Richard L. Harkess, Geoffrey C. Denny, and Carolyn Scagel

point; width 2, perpendicular width of width 1) of each plant were measured every 2 weeks. Plant growth index (PGI) was calculated as the average of the plant height and two widths. Leaf chlorophyll content was estimated by leaf SPAD reading. Leaf SPAD

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Y.C. Li, A.K. Alva, D.V. Calvert, and M. Zhang

Rapid and accurate diagnosis of plant nutrient deficiency is critical for growers to use fertilizer economically and to minimize environmental concern. The objective of this study was to evaluate the use of leaf chlorophyll meter (SPAD-502) to predict nitrogen status and yield response of grapefruit trees. The study includes two irrigation treatments, three fertilizer sources, and four fertilizer rates. No significant differences in SPAD readings and leaf N were found between two irrigation treatments. Correlations between SPAD readings and leaf N were higher for the spring flush (r = 0.61) than that for summer flush (r = 0.49). There were poor relations between SPAD meter readings and the extractable chlorophyll content in the spring flush on a dry-weight basis (r = 0.25). Higher correlations between SPAD meter readings and N rates or fruit yields than between leaf N concentrations and N rates or fruit yield.

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Denise Neilsen, Eugene J. Hogue, Gerald H. Neilsen, and Peter Parchomchuk

Four apple (Malus domestica Borkh) cultivars (`Fuji', `Spartan', `Fiesta', and `Gala') on Malling 9 (M.9) rootstock were grown in the field with three N rates (5, 20, and 35 g N/tree per year), supplied as Ca(NO3)2, and fertigated daily for 9 weeks. In the second year, leaf SPAD readings (chlorophyll readings obtained with the Minolta-502 SPAD meter) increased over the growing season for all cultivars, and leaf N decreased. Leaf SPAD and leaf N measurements increased in response to N fertigation rate at all sampling times. `Gala' consistently had lower SPAD readings than the other cultivars, and, with the exception of the first sampling time, `Fuji' had higher and `Fiesta' lower leaf N concentrations than other cultivars. There were strong relationships between leaf N concentration and SPAD readings for all cultivars until mid-July (r 2 = 0.44 to 0.89), but not later in the growing season. Differences in SPAD readings and leaf N concentration due to cultivar and over time were as great as those due to N treatments, indicating that in the future, determination of critical SPAD values for apple leaves must be standardized for cultivar and sampling time. SPAD readings could be used to assess the need for N early in the growing season in fertigated orchards where rapid changes in nutrition programs can be undertaken readily.

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Yanjun Guo, Terri Starman, and Charles Hall

) measured with a chlorophyll meter (SPAD-502; Minolta Camera Co., Osaka, Japan), and predawn and midday leaf water potential with a pressure bomb (Soil Moisture Equipment Corp., Santa Barbara, CA). SPAD readings ranged from 0 to 100 by measuring the light

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Yuru Chang, Lorenzo Rossi, Lincoln Zotarelli, Bin Gao, and Ali Sarkhosh

regulating the activities of microbial enzymes in soil ( Chen et al., 2011 ; Zhai et al., 2015 ). Muscadine grape physiological performance. There was no significant difference in SPAD readings among the treatments ( Fig. 4 ). Similarly, Quilliam et al

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Shasha Wu, Youping Sun, Genhua Niu, James Altland, and Raul Cabrera

consider the plant size. Leaf greenness. Leaf greenness (or relative chlorophyll content, SPAD reading) was measured using a handheld chlorophyll meter (measured as the optical density; Minolta Camera Co., Osaka, Japan) at the end of the experiment (on 3