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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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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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Thiago Vieira da Costa, João Alexio Scarpare Filho, and Matthew W. Fidelibus

). Every plot received ≈1.15 L of the appropriate chemical solution. Sprays were directed to foliage on fruiting canes, leaving renewal shoots untreated. A SPAD meter (SPAD-502; Konica Minolta, Osaka, Japan) was used to monitor changes in leaf greenness, as

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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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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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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)..

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Pinghai Ding*, Jessica M. Cortell, and Leslie H. Fuchigami

Nitrogen is one of the most important nutrition factors affecting grapevine growth performance and berry quality. Leaf pigments contents and leaf areas are the important indicators of grapevine nitrogen status and plant performance. In order to find a efficient way to nondestructively measure leaf nitrogen and pigments status, the SPAD meter, CCM-200 and CM-1000 chlorophyll meter in comparisons with FOSS NIR system were used in measuring leaf nitrogen, leaf chlorophyll, carotenoids, flavonoids and anthocyanins in 7-year-old Pinot Noir grape with different rate of N treatments. The results indicate that the reading of all these meters have a good relationship with leaf N, leaf chlorophyll and leaf area. But the accuracy among these meters was different, in which the accuracy of FOSS NIR is better than that of the SPAD meter, CCM-200 and CM-1000. There is the good relationship between leaf nitrogen contents, leaf area, leaf chlorophyll and carotenoids contents. Flavonoids and anthocyanins have the inverse relationship with leaf N contents and leaf area. FOSS NIR system can be use for nondestructive assessing nitrogen, leaf chlorophyll, carotenoids, flavonoids and anthocyanins whereas the other meters can only used for nondestructive assessing leaf nitrogen and leaf chlorophyll. These results indicate it is possible to use nondestructive spectral methods as the precision viticulture tools to manage vineyards nitrogen fertilization and grapevine performance.

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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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Olivia M. Lenahan and Matthew D. Whiting

This article reports on the physiological effects and horticultural benefits of chemical blossom thinners on 9-year-old and 12-year-old `Bing'/`Gisela®5′ sweet cherry trees in 2004 and 2005, respectively. Chemical thinning agents were applied at 20% and 80% full bloom (FB) by air-blast sprayer and were comprised of: 2% ammonium thiosulphate (ATS), 4% vegetable oil emulsion (VOE), 2% fish oil + 2.5% lime sulfur (FOLS), 1% tergitol, and an untreated control. Leaf gas exchange, leaf SPAD meter readings, chlorophyll fluorescence parameters, fruit yield, and fruit quality were evaluated. FOLS, tergitol, VOE, and ATS suppressed leaf net CO2 exchange rate (NCER) by 33%, 30%, 28%, and 18%, respectively, over a variable length recovery period directly after 80% FB treatment. Leaf NCER recovered fully from every thinning treatment. Reductions in leaf NCER were unrelated to gS. VOE reduced estimated leaf chlorophyll content the greatest, suppressing overall levels by 11% for 23 days after treatment. All blossom thinners reduced constant fluorescence (Fo). No thinning agent reduced fruit set or yield in 2004. ATS, FOLS, and tergitol reduced fruit set in 2005. VOE was ineffective as a thinner yet exhibited significant leaf phytotoxicity. Among thinners, there was no relationship between inhibition of leaf NCER and thinning efficacy.