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Bruce L. Dunn and Carla Goad

( Wang et al., 2004 ). Use of optical sensors allows for an increased number of plants and leaves to be analyzed and results are immediately available ( Mielke et al., 2012 ). The SPAD (SPAD-502; Konica Minolta, Japan) is widely accepted in the agronomic

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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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Jeff L. Sibley, D. Joseph Eakes, Charles H. Gilliam, Gary J. Keever, William A. Dozier Jr., and David G. Himelrick

Twelve red maple selections in an existing field trial were evaluated for leaf chlorophyll content with a SPAD-502 chlorophyll meter, total foliar N concentration with a LECO CHN analyzer, and total foliar chlorophyll content (CHL) by N,N-dimethylformamide extraction. Selections included Acer rubrum L. `Autumn Flame', `Fairview Flame', `Franksred' (Red Sunset™), `Karpick', `Northwood', `October Glory', `Redskin', `Schlesingeri', and `Tilford', and A. ×freemanii E. Murray `AutumnBlaze' (`Jeffersred'), `Morgan' (`Indian Summer'), and `Scarsen' (Scarlet Sentinel™). `Franksred' and `Northwood' had the highest monthly SPAD-502 values in 1993 and 1994. Lowest SPAD-502 values were on `Redskin' and `Autumn Blaze' each year. Foliar N concentration ranged from 2.62% for `Autumn Flame' to 2.01% for Redskin. CHL levels on a fresh-weight basis ranged from 5.38 mg·g–1 for `Fairview Flame' to 3.94 mg·g–1 for `October Glory'. SPAD-502 and extractable CHL values were correlated (r = 0.45; P ≤ 0.001); however, the correlation (r = 0.15; P ≤ 0.38) between SPAD-502 values and total foliar N concentration was nonsignificant.

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Giampaolo Zanin and Paolo Sambo

Rosa chinensis Jacq. var. mutabilis plants were grown in a greenhouse to determine whether a hand-held chlorophyll meter (SPAD-meter) is suitable for the plant N status assessment. Therefore, plants were fertilized with increasing levels of N, applied through urea form as top dressing. The doses were: 0, 0.15, 0.3, 0.45, 0.6, and 0.75 g of N per liter of substrate. Periodically during the growing season, plant height and width, fresh and dry weight of different plant organs at 10, 20, and 30 weeks after planting, and their total N, plant P, and K were measured. Furthermore, six times along the growing cycle, the amount of chlorophyll in leaves was estimated using a SPAD-meter and analytically measured by chlorophyll extraction with ethanol and reading through a spectrophotometer. In the same leaves, N concentration was also determined. Treatments with 0.45–0.6 g of N per liter of substrate gave the tallest and widest plant. Plant weight and flower production were also the highest with these doses. The concentration of organic N in plant organs increased along with the N availability in the substrate, which suggests that a “luxury consumption” took place. The SPAD values showed high correlation among chlorophyll and N concentrations. Values that ranged between 35–40 seemed to mean good nutrient status. A high correlation was also found among SPAD values and some of the productive characteristics, which indicates that a SPAD-meter is a suitable tool in the dynamic fertilization of rose.

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Francis X. Mangan, John Howell, and Stephen Herbert

Hot cherry peppers were grown after incorporation of the following three winter cover crop regimes in Summer 1994—hairy vetch (Vicia villosa) plus winter rye (Secale cereale), hairy vetch alone, and no cover crop. For each main effect there were three N rates applied to peppers in three applications over the course of the season: 0, 85, and 170 kg·ha–1. The pepper yield was significantly higher with hairy vetch plus rye than rye alone or no cover crop. There was also no significant yield increase with the addition of N fertilizer to the peppers grown with hairy vetch. Soil nitrate–N levels taken just prior to N sidedress were significantly higher in plots that had hairy vetch plus rye compared to other treatments. There was also a significant linear relationship of the soil nitrate–N levels among the three N rates. Based on the results of this study, sidedressing peppers would be recommended when soil nitrate levels are above the 25 ppm that is the current threshold for other crops. SPAD readings were taken several times during the season. There was a high correlation of SPAD readings to pepper yield very early and very late in the season. The correlation of SPAD readings to pepper yield was poorest when taken at the time of N sidedress.

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Panayiotis A. Nektarios, Ioannis Amountzias, Iro Kokkinou, and Nikolaos Ntoulas

separated from the substrate by rinsing with water. The fresh weight of the aerial plant portion was determined by weighing, and then all plant parts were placed in a drying oven at 70 °C for 4 d to determine leaf and stem dry weights. SPAD and chlorophyll

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Felix C. W. Loh, Jason C. Grabosky, and Nina L. Bassuk

A Minolta SPAD-502 leaf chlorophyll meter was used for nondestructive data collection on the chlorophyll and nitrogen (N) status of benjamin fig (Ficus benjamina) and cottonwood (Populus deltoides) to quantitatively evaluate foliage quality. The goal was to provide a specific calibration for interpreting SPAD data within a media study for each species. Triplicate SPAD readings were collected from each of six leaves, sampled from forty plants per species, then processed for foliar analysis. Leaf tissue disks were also collected directly over SPAD testing sites for chlorophyll concentration measurement. Significant linear correlations were found between SPAD data and chlorophyll concentrations (r 2 = 0.90 in benjamin fig and r 2 = 0.91 for cottonwood). A significant, but lower correlation was found between SPAD data and N concentration. The SPAD-N correlations improved from the fifth month to the ninth month harvest (r 2 = 0.32 to 0.53 for benjamin fig and 0.26 to 0.42 for cottonwood). The SPAD-502 could be useful for in landscape plant management, and in time for production situations, but baseline data is needed. Consistent protocol in sample collection and seasonal timing is needed prior to use as a predictor for tissue N levels. Development of species, and perhaps cultivar, specific baseline data and sampling procedures will need development, but could yield a rapid, quantitative, in expensive field diagnostic for foliage quality for making cultural management decisions.

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Ajay Nair, Mathieu Ngouajio, and John Biernbaum

, NV). Leaf chlorophyll content of the recently emerged, fully opened true leaf was recorded with a chlorophyll meter (SPAD-502 Chlorophyll Meter; Minolta Camera Co. Ltd., Osaka, Japan). The SPAD values were means of 10 leaf measurements. Before seeding

Open access

Kristine M. Lang, Ajay Nair, and Kenneth J. Moore

deionized water to an endpoint of pH = 8.1 with sodium hydroxide. Leaf chlorophyll concentration. An indirect estimate of leaf chlorophyll concentration was measured during each growing season using a SPAD-502 Plus chlorophyll meter (Konica Minolta Sensing

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Felix Loh, Jason Grabosky, and Nina Bassuk

The Minolta SPAD meter has been used to evaluate chlorophyll concentration in plant material to provide an inexpensive method to collect rapid, nondestructive data. Correlations of SPAD data and chlorophyll concentrations in corn have been very accurate r 2 = 0.95), and can be used to monitor plant nutrient status as a function of chlorophyll concentration. There has been evidence that the calibrated accuracy of the SPAD meter is diminished at low and high concentrations of chlorophyll. Our study attempted to build the same type of background information for two tree species for use in evaluating plant response in experimental media experiments. Ficus benjamina L. and Populus deltoides Marsh were grown in containers of varied media. Leaf tissue was measured with a Minolta SPAD-502, and the tissue was then removed and processed with N,N-dimenthylformamide for analysis in a spectrophotometer. The remainder of the leaf sample was analyzed in an ICAP for tissue nutrient levels. Data were analyzed to evaluate the usefulness of the SPAD meter for woody plant leaf tissue evaluation and to develop calibration curves for use in future studies. There was a positive correlation (r 2 = 0.943 in Ficus) between SPAD data and combined concentrations of chlorophyll a and b. Accuracy of the SPAD data was diminished when chlorophyll concentrations were low (SPAD <20, chorophyll <450 μg·mL-1) and high (SPAD >45, chorophyll >1350 μg·mL-1)..