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P.L. Minotti, D.E. Halseth, and J.B. Sieczka

We report three N rate experiments conducted on a gravelly loam soil to assess the N status of potato (Solanum tuberosum L.) using a Minolta SPAD-502 chlorophyll meter. Highly significant linear and quadratic trends were obtained for the regression of N rate on marketable tuber yields and SPAD readings. SPAD readings were taken at four times during the growing season and decreased as plants aged. Based on regression analysis, the early season SPAD readings, associated with N rates giving maximum marketable tuber yields, ranged from 49 to 56 units depending on year, variety, and location. Potato variety significantly affected SPAD values in eight of the 12 situations where readings were obtained. Precision in interpretation was improved when the highest N rates were considered “reference strips” to standardize the SPAD readings across varieties and growing seasons. Our results suggest that field SPAD readings can readily identify severe N deficiency in potatoes, have the potential to identify situations where supplementary sidedressed N would not be necessary, but would be of limited value for identifying situations of marginal N deficiency unless reference strips are used.

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Qiang Liu, Youping Sun, James Altland, and Genhua Niu

photosynthesis system with an automatic universal PLC6 broad leaf cuvette (CIRAS-2; PP Systems, Amesbury, MA) 1 d before the first and second harvest. Relative chlorophyll content (SPAD reading) was also measured using a handheld chlorophyll meter (measured as

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Richard J. Campbell, Kendrick N. Mobley, Richard P. Marini, and Douglas G. Pfeiffer

The relationship between SPAD-501 meter readings (SPAD) and total chlorophyll content (TCHL) was evaluated for `Delicious' apple (Malus domestica Borkh.) leaves grown in various environments. Regression models were developed between SPAD and TCHL for each of six separate experiments and were evaluated for statistical coincidence. SPAD was linearly related in a positive manner to TCHL in five of the six experiments; however, models differed between experiments, particularly between field- and greenhouse-grown trees. Thus, the relationship between SPAD and TCHL must be determined for each experiment.

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Chad T. Miller, Neil S. Mattson, and William B. Miller

diameter being calculated as the average of two perpendicular measurements, and SPAD meter readings (Minolta Chlorophyll Meter SPAD-502; Spectrum Technologies, Plainfield, IL) of five randomly selected leaves, one per experimental unit (plant), to determine

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

The objective of this study was to evaluate the use of a leaf chlorophyll meter (SPAD-502) to predict nitrogen status and yield response of grapefruit trees. The study included two irrigation treatments, three sources, and four rates of fertilizer [dry soluble granular fertilizer broadcast or through fertigation with N rates either 50, 100, 150 lb/acre/yr (56, 112, or 168 kg.ha-1.yr-1)], and controlled-release fertilizer with N rates either 25, 50, 100 lb/acre. Irrigation treatments did not affect SPAD readings and leaf N concentrations. Correlations between SPAD readings and leaf N were greater for the spring flush (r 2 = 0.61) than for the summer flush (r 2 = 0.49). High correlations of SPAD meter readings with either fruit yields or leaf N suggests that SPAD meter reading is an acceptable index of N status and fruit production of the trees. SPAD readings can be made rapidly without destructive sampling of the leaves. This study demonstrates that the SPAD meter can be used to evaluate the tree N status and improve a N fertilization program for grapefruit trees.

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Ajay Nair and Brandon Carpenter

from the top, five SPAD readings were taken and averaged. Ten plants were sampled from each treatment. To determine total dry weight (root + shoot), roots were gently shaken to remove medium, washed, and cut at the medium line. Roots and shoots were

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Tongyin Li, Guihong Bi, Richard L. Harkess, Geoffrey C. Denny, Eugene K. Blythe, and Xiaojie Zhao

height, width 1, and width 2. Three fully expanded new leaves were selected from each plant to measure their leaf SPAD reading using a chlorophyll meter (SPAD 502 Plus; Konica Minolta, Tokyo, Japan) on the same interval as plant height and widths. An

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Robert E. Rouse, Sandra P. Perez, and Sally B. Davenport

The Minolta chlorophyll meter SPAD-502 (Minolta Camera Company, 101 Williams Drive, NJ 07446, USA) was evaluated as an accurate, nondestructive means to measure chlorophyll content in citrus leaves. Meter readings from leaves of sweet orange and grapefruit citrus cultivars were used to develop a standard curve for citrus. A significant correlation value of 0.96 was calculated between the chlorophyll meter readings and actual chlorophyll extraction levels. The development of a standard curve using the SPAD-502 chlorophyll meter had not been established on citrus. The SPAD-502 chlorophyll meter proved to be a quick, accurate, simple, and nondestructive way to determine chlorophyll content in citrus leaves.

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Ian R. Rodriguez and Grady L. Miller

Because high rates of nitrogen fertility are necessary for producing high-quality turfgrasses, quick, reliable methods of determining the N status of turfgrasses would be valuable management tools. The objective of this study was to evaluate the capacity of a hand-held chlorophyll meter (SPAD-502) to provide a relative index of chlorophyll concentrations, N concentrations, and visual quality in St. Augustinegrass [Stenotaphrum secondatum (Walt.) Kuntze]. Two experiments were conducted in a greenhouse in 1998 to evaluate the utility of SPAD readings. Established pots of `Floratam' were subjected to weekly foliar Fe treatments at Fe rates of 0 and 0.17 kg·ha–1 for 4 weeks. Six weekly nitrogen fertilizer treatments were applied in the form of ammonium sulfate at N rates of 0, 5.75, 11.5, 17.25, and 23 kg·ha–1 for 4 weeks. Greenhouse SPAD readings were not affected by Fe treatment, but N treatments resulted in differences in SPAD readings, visual quality, and chlorophyll concentrations. The readings were positively correlated with chlorophyll concentrations (r 2 = 0.79), visual ratings (r 2 = 0.74), and total Kjeldahl nitrogen (TKN) (r 2 = 0.71). Readings taken from field-grown `Floratam', `Floratine', and `Floralawn' St. Augustinegrass were poorly correlated (r 2 < 0.63) with chlorophyll concentrations and TKN. Unless future techniques improve dependability of the SPAD meter under field conditions for measuring chlorophyll and N concentration of a stand of turfgrass, the usefulness of such readings for the management of St. Augustinegrass seems limited.

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Fairuz A. Buajaila, Pinki Devi, and Carol A. Miles

was assessed in all cases using Levene's test, and normality by Shapiro-Wilk test (W > 0.80). Data for SPAD meter readings and nitrate-N measurements were transformed for statistical analysis to meet the assumptions of normality and homogeneity of