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Kristine M. Lang and Ajay Nair

production (28 Aug. 2015 and 20 Aug. 2016), an indirect estimate of leaf chlorophyll concentration was measured with a SPAD-502 Plus chlorophyll meter (Konica Minolta Sensing America Inc., Ramsey, NJ). Five readings were taken on the first fully developed

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

America Inc., Ramsey, NJ). After placement of shadecloth treatments, SPAD measurements were collected three times in 2017 and five times in 2018 ( Table 2 ). Five readings were collected on the first fully developed leaf of each plant, and measurements

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Xuan Liu and Donald L. Suarez

observation, after lima bean leaf gas exchange reached a steady-state, further time elapse of several minutes made little change on the readings). Leaf SPAD chlorophyll readings were taken six times across the whole leaf blade vertically and horizontally

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Anna L. Hale, Douglas C. Scheuring, Thomas J. Gerik, Jeffrey D. Hart, and J. Creighton Miller Jr.

Iron Deficiency Chlorosis (FeDC) is a problem in cowpea because it affects the ability of the plant to produce chlorophyll. Earlier studies indicated that FeDC was conditioned by a single gene. Pinkeye Purple Hull (PEPH), a susceptible variety, and Texas Pinkeye Purple Hull (TXPE), a resistant variety, were crossed and allowed to self for one generation. The F1s were backcrossed to the parents. SPAD readings were taken on each population. SPAD measures the transmission of light through the leaves at a wavelength where chlorophyll absorbs and a wavelength where it does not. The SPAD reading is calculated based on a ratio of these two numbers. Thus, the SPAD value is unitless and is an indication of the relative amount of chlorophyll present in the leaf. Chlorophyll was extracted from leaves, and regressed on the SPAD readings from the same leaves. An R 2 of .9102 was obtained as well as a regression equation of y = 12.8x + 54.5. Thus, a SPAD value of 1 corresponds with a chlorophyll content of ≈67.3 μg chlorophyll/gfw. The data was analyzed using a bootstrap method, and indicated that FeDC is not controlled by a single gene. A P-value of .0004 showed a highly significant difference between the expected and observed segregation ratios in the F2 plants. Narrow sense heritibility (Mather) was estimated at 0.3.

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Anthony F. Silvernail and Gary R. Cline

The effects of cover crop, tillage, and N fertilization on yields of `Paladin' watermelon (Citrullus lanatus) were analyzed by determining available soil N levels, foliar N content, and relative greenness with a SPAD-502 chlorophyll meter. Analyses from all three analytical procedures identified N deficiencies in watermelon with their respected measurements. Available soil N analyses indicated that soil N levels below 40 mg·kg–1 at vining caused dramatic decreases in yields, while the level needed to ensure maximal yields during the same period was 100 mg·kg–1. Results from foliar and SPAD tests indicated that plants with foliar N levels below 42 g·kg–1 and SPAD readings below 40 SPAD units at anthesis will have suppressed yields. Optimal foliar N levels and SPAD readings required for maximum yields were 50 g·kg –1 and 48 SPAD units, respectively. The main difference among all three N testing procedures was that available soil N analysis was able to detect possible deficiencies two to three weeks before either the foliar or SPAD analysis. Differences in yield between plants from conventionally tilled plots and no-till plots were not significant. However, inorganic N fertilization significantly increased yields in watermelon following both rye (Secale cereale) and mix cover crop treatments. Watermelon yields of plants following the hairy vetch (Vicia villosa) cover crop treatment showed no response to inorganic N fertilization. Of the three cover crop treatments, the addition of N fertilizer had the most effect in the rye treatment.

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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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Sean M. Westerveld, Alan W. McKeown, Mary Ruth McDonald, and Cynthia D. Scott-Dupree

Nutrient management legislation has prompted an evaluation of alternative nitrogen (N) management techniques. SPAD (Soil Plant Analysis Development) chlorophyll and Cardy nitrate (NO3 -) meters were evaluated for their potential as tissue nitrogen tests in cabbage (Brassica oleracea var. capitata), onions (Allium cepa), and carrots (Daucus carota subsp. sativus). Cabbage, carrots, and onions were grown on both organic and mineral soils in Ontario, Canada in 2000 and 2001. Nitrogen was applied at five rates to cabbage and carrots and three rates to onions ranging from 0 to 200% of current provincial recommended N rates. In an additional treatment, 50% of the recommended rate was applied preplant and sidedress N applications of 40 kg·ha-1 (35.7 lb/acre) were applied when SPAD chlorophyll meter readings fell below 95 (2000) and 97% (2001) of the highest N rate treatment. Yields were generally unaffected by N rate, except in cabbage in 2000, suggesting adequate N was present in most treatments. SPAD chlorophyll meter readings were highly variable among soil types, cultivars, and years. Chlorophyll readings reached a plateau in adequately fertilized crops in many instances. Cardy readings were less variable among soil types, cultivars, and years. The relationship between N rate and sap NO3-N concentration was generally linear. The results suggest that the use of a well-fertilized reference plot is most appropriate for the SPAD meter on these vegetable crops, while the use of region-specific critical NO3-N concentrations was most appropriate for the Cardy NO3-meter. Both meters would be cost advantageous when over 500 samples are tested. The meters were generally easy to use, except for the SPAD meter on carrots. The meters have potential for N management of vegetable crops under Ontario growing conditions.

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James E. Altland, Charles H. Gilliam, Gary J. Keever, James H. Edwards, Jeff L. Sibley, and Donna C. Fare

Two experiments were conducted with pansy (Viola ×wittrockiana Gams `Bingo Yello') to determine the relationship between foliar nitrogen (% of dry weight) (FN) and either sap nitrate concentration (SN) in petioles or SPAD readings of foliage. FN was highly correlated to SN throughout both experiments (r = 0.80 to 0.91). FN was poorly correlated to SPAD readings early in both experiments (r = 0.54 to 0.65), but more highly correlated later when visual symptoms of N deficiency were apparent (r = 0.84 to 0.90). SN determined with the Cardy sap nitrate meter was a reliable predictor of FN in pansy, while SPAD readings were only reliable after symptoms of N deficiency were visually evident. FN can be predicted with SN using the following equation: log(SN) = 0.47*FN + 1.6 [r 2 = 0.80, n = 132]. Growers and landscape professionals can use SN readings to predict FN levels in pansy, and thus rapidly and accurately diagnose the N status of their crop.

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M. Wilcox, C.A. Sanchez, and T.M. Blackmer

Several studies in the midwestem United States have shown that chlorophyll meter readings (Minolta SPAD 502) are useful in determining the N status of corn (Zea Mays L.), and show promise as a tool for the efficient N management of corn. Studies were conducted to evaluate the potential of the `chlorophyll meter for evaluating N deficiencies in lettuce (Lactuca sativa L.). Data for chlorophyll meter readings, midrib nitrate-N, lettuce growth rate, and marketable lettuce yield were collected in five N fertility experiments in 1993 and 1994. Chlorophyll meter readings not only varied among lettuce types (butter, cos, leaf, crisphead), but also among cultivars of the crisphead type. Chlorophyll meter readings were generally poorly correlated to midrib nitrate-N levels and marketable lettuce yield. Lettuce leaves have more color variation than corn leaves, and perhaps this variation in relation to the small sensor size on the SPAD 502 confounded readings. The observation that subtle N deficiencies in lettuce are usually manifested in growth rate reduction rather than abrupt color changes may also limit the usefulness of the chlorophyll meter for lettuce.

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Robert E. Rouse

The Minolta chlorophyll meter SPAD-502 (Minolta Camera Company, 101 Williams Drive, NJ 07446, USA) has been found to be a quick, accurate, simple, and nondestructive way to determine chlorophyll content in citrus leaves and a standard curve had been developed. The SPAD-502 chlorophyll meter was used to measure chlorophyll content in citrus leaves of ten varieties on three rootstocks. Leaf mineral analysis was then determined on these leaves for N, P, K, Mg, Mn, Zn, Fe, Cu and Ca. Correlation r values were generally low and not significant for most nutrient elements but were highest for Fe and Ca. The relationship of leaf nutrient levels and chlorophyll meter readings are not understood. The usefulness of the SPAD chlorophyll meter for determining mineral content in citrus leaves is not yet known.