Hand-held Chlorophyll Meter Research Articles

Spectral and spatial differences in response of vegetation indices to nitrogen treatments on apple

Handheld chlorophyll sensors and remote sensing are two nondestructive approaches for estimating plant nitrogen (N) status, which are now commercially available. In this paper we address three questions on the application of these technologies in perennial fruit trees: (1) can individual leaf meter measurements be used to predict N status for surrounding trees?, (2) are narrow band indices more sensitive than the normalized difference vegetation index (NDVI) to differences in plant N?, and (3) is NDVI from satellite remote sensing correlated to leaf level vegetation indices? We evaluated data from a N rate trial conducted in a commercial Fuji apple orchard ( Malus domestica Borkh. cv. ‘Fuji’) . SPAD and CM1000 handheld chlorophyll meters and reflectance measurements using a portable spectrometer were made on individual leaves three or four times during each growing season. The reflectance measurements were used to determine NDVI and three narrow band vegetation indices. Satellite imagery from the Quickbird sensor was acquired two or three times during each growing season and used to generate NDVI for individual trees. The leaf meter measurements and vegetation indices were compared with the N application rate and plant N status measured as total leaf tissue N. We evaluated how well single leaf meter measurements predict N status for surrounding trees by calculating the differences between actual and estimated N applications from individual measurements. On average, a sample of 12 leaves (from the same treatment and same measurement date) resulted in an estimation error of 30 kg ha −1 for either the SPAD or the CM1000 sensor, representing almost half of the range in N treatment rates. To evaluate any improvement in prediction of applied N using narrow band indices, we used analysis of variance (ANOVA) to compare three narrow band indices with the leaf meters and NDVI measured at leaf and canopy levels. Two narrow band indices, red edge vegetation stress index (RVSI) and modified chlorophyll absorption in reflectance index (MCARI) had higher F-values (31 and 41, respectively) than did NDVI from leaf level measurements (26), from satellite NDVI (6), or the CM1000 chlorophyll meter (12). The ANOVA results support improvements in leaf sensors using index values other than NDVI. We found that NDVI from satellite imagery acquired close to the leaf level measurement dates were positively correlated to the chlorophyll sensors and vegetation indices. When the data was averaged to the experiment plot level (twelve leaves total), the correlation coefficients between the satellite NDVI and the other sensors ranged from 0.68 for NDVI from leaf level reflectance to 0.84 with the CM1000 chlorophyll meter. Given the level of correlations, remote sensing might be a useful tool to extrapolate handheld measurements spatially throughout an orchard.

Improving Growth of Calibrachoa in Hanging Flower Pouches

Unique growing containers and nontraditional types of plant presentation may lead to new production problems for growers. This study was conducted to evaluate the growth of a popular container plant, calibrachoa (Calibrachoa ×hybrida), produced in hanging flower pouches using different growing substrate compositions, polymer amendments, and the layering of substrate types of differing moisture holding capacity with the goal of achieving more uniform plant growth and improved after-sale maintenance. Plastic cylindrical hanging pouches were filled with one of nine hydrated substrate types or combinations. Rooted cuttings of ‘Colorburst Violet’ calibrachoa were planted as indicator plants to identify treatment effects because of their susceptibility to iron deficiency-induced chlorosis of new leaves. Daily measurements of substrate moisture were taken to determine the need for irrigation. Chlorophyll content was estimated nondestructively with a hand-held chlorophyll meter to determine the impact of moisture content. Light, porous substrates resulted in the most uniformly green plants and high numbers of flowers from top to bottom. A layered pouch with heavy, compost-amended substrate above a light, porous layer also produced high-quality, uniform plants. This enabled water to be distributed more uniformly throughout the container volume. This study provides fundamental information on how container geometry and soil moisture retention can influence water management decisions by the grower.

Split nitrogen application strategies in seed production of two contrasting cultivars of timothy (Phleum pratense L.)

Split nitrogen (N) application to seed crops of timothy (Phleum pratense L.) was evaluated in 20 field trials, 11 in the south-Norwegian cultivar ‘Grindstad’ (origin 59°N) and nine in the north Norwegian cultivar ‘Vega’ (origin 67°N) in southeast (58–61°N) and central (63–64°N) Norway during 1998–2000. Three N rates (25, 50 or 75 kg N ha−1) at the start of growth were combined with four N rates (0, 25, 50 or 75 kg N ha−1) at the start of tiller elongation (Z 31). On average for all trials, the highest seed yield was obtained when a total rate of 75 kg N ha−1 was split into a main application of 50 kg N ha−1 at the start of growth and a supplemental application of 25 kg N ha−1 at Z 31. In both cultivars, the optimal N rate at Z 31 was uncorrelated with soil mineral N (NO3+NH4) in early spring and only weakly correlated (r 2=0.16–0.17, p% = 2–5) with the N concentration of aboveground plant material at Z 31. In ‘Grindstad’, a better correlation (r 2=0.46, p% < 0.1) was obtained between the optimal N rate at Z 31 and measurements by the hand-held chlorophyll meter Hydro N-Tester™ on the last fully developed leaf. The equation (HTN model) Optimal N input (kg N ha −1 ) at Z 31 = − 0.37×measured HNT value at Z 31+156 was further evaluated in ten on-farm trials during 2001–2002. Compared to the fixed N levels 0, 25 or 50 kg N ha−1, the HNT model predicted optimal N rates at Z 31 in 2002, but not in 2001, when less rainfall caused less lodging than in 1998–2000 and 2002. Nevertheless, we conclude: 1) that the spring N rates to timothy seed crops should be split into an early and a late application, and 2) that the HTN model will help in adjusting the second N rate at Z 31 in ‘Grindstad’.

Using SPAD-meter in Nitrogen Fertilization of Rosa chinensis Jacq. var. mutabilis

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.

Nitrogen Measurement for Variable‐Rate N Management in Maize

Numerous proximal and remote soil and plant‐testing methods are available to guide variable‐rate N management in maize production. These include preseason and late spring soil nitrate tests, late season stalk nitrate tests, handheld chlorophyll meter readings, remote sensing of soil and crop canopy properties, site‐specific data from yield monitors and soil electrical conductivity maps. Field applicators have even been equipped to sense the N status of a crop and direct the application of any needed N on‐the‐go. However, the adoption rates of variable‐rate N management are low worldwide despite the potential economic and environmental benefits of this practice and the availability of variable‐rate application technology in key areas of maize production. A major obstacle is the finding that recommended N fertilizer rates based on yield goal are often poorly correlated with actual economically optimum N rates. Nitrogen response patterns are often field and season specific and can vary widely within the same field, further complicating adoption. Paired field comparisons of uniform‐ and variable‐rate N management have revealed no consistent advantages for either strategy in yields achieved, whole‐field N usage or N use efficiency by plants. Research with other agronomic crops also indicates that the scale for determining crop N need may be as low as 1 m2. An additional constraint is that growers implementing variable‐rate N techniques often are required to install several adequately fertilized N reference strips in their fields that have proven to be both hybrid and season specific. In addition to these agronomic and logistical challenges, the maximum potential benefit of a variable N strategy vs. a conventional uniform‐rate N strategy is typically between 12 and 37 USD($)/ha. When the cost of developing and executing the variable‐rate strategy is considered, the practice shows a low economic return. In the future, innovations in N soil testing, better crop simulation models, and improved N sensing and application equipment may assist growers in capturing the benefits of site‐specific N management in maize production.

Quality and Nitrogen Use Efficiency of Sunflower Grown at Different Nitrogen Levels Under Mediterranean Conditions

A two-year field experiment (during 1998 and 1999) was carried out in a Mediterranean environment to study the effects of different nitrogen (N) fertilizer rates on N uptake, N remobilization, N use efficiency, and yield performance of sunflowers grown in Southern Italy. Two sunflower genotypes (one commercial standard line and one selected genotype) and three N fertilization levels (0, 50, and 100 kg ha−1 as ammonium nitrate) were compared in this experiment. N uptake (N content × biomass dry weight) of the leaves and stems, hand-held chlorophyll meter (SPAD readings), and leaf area index (LAI) were measured at flowering time; yield and its components, percentage of oil content, and plant N uptake were determined at physiological maturity. Nitrogen use efficiency parameters and N remobilization were also calculated. The results indicated a significant difference in yield, percentage of oil content, total N uptake, and N use efficiency parameters between the years, indicating greater limits imposed by the environment on sunflower potential. In the year with irregular rainfall (1998), higher N uptake at the flowering stage was found, thus determining higher N translocated, whereas in the year with normal rainfall distribution (1999), a higher total N uptake at the maturity phase was recorded. The intermediate N fertilization treatment (50 kg N ha−1) showed a better utilization of applied N, reducing the possibility of pollution. In fact, in both years, yield, LAI, total N uptake, and N use efficiency were statistically unaffected by the two N fertilization treatments. The differences between sunflower genotypes in yield performance and N use efficiency were observed during 1999, when the climate did not limit sunflower growth. In contrast, during 1998 N fertilization rates showed a significant response to the N fertilizer treatments in yield and in most measured parameters. Finally, the significant correlation between N uptake and N use efficiency parameters with yield indicate the importance of N nutrition in sunflowers grown in Mediterranean conditions, whereas the negative correlation between yield and oil content confirms that higher seed production is associated with lower oil content.

Growth, Nutrient Status, and Chlorophyll Meter Readings in Wheat as Affected by Nitrogen and Manganese

Mineral nutrition of wheat (Triticum aestivum L.) in highly calcareous soils low in available nitrogen (N) and manganese (Mn) requires further investigations. The purpose of this experiment was to determine the effect of N and Mn on the growth, nutrient concentration and uptake, and chlorophyll meter readings (CMR) in wheat grown in greenhouse conditions. The experiment was conducted on a highly calcareous soil (fine-loamy, carbonatic, thermic, Typic Calcixerepts) relatively low in available N and Mn. Treatments consisted of a factorial arrangement of five N rates (0, 50, 100, 200, and 400 mg kg−1 as NH4NO3) and three Mn levels (0, 15, and 30 mg kg−1 as MnSO4) in a completely randomized design with four replications. Plants were grown for 60 d and hand-held chlorophyll meter (Minolta SPAD-502) readings were used to evaluate dry matter (DMY) and N, Mn, iron (Fe), zinc (Zn), and copper (Cu) concentration of wheat in aerial parts. Applied N increased DMY and concentration and uptake of N, Mn, Fe, Zn, and Cu, and Mn:Fe ratios. A significant correlation was obtained between DMY and applied N (R2 = 0.75). Manganese had no significant effect on DMY, N, Zn, Cu concentration and uptake, and Fe uptake. However, Mn rate increased Mn concentration and uptake and Mn:Fe ratio and reduced Fe concentration. Interaction of N × Mn did not affect DMY, concentration, or uptake of any of the nutrients. The CMR increased significantly with N rate but was not influenced by Mn addition. Highly significant correlations were observed between CMR and DMY (R2 = 0.84), and the concentrations of N (R2 = 0.97), Mn (R2 = 0.70), Fe (R2 = 0.73), Zn (R2 = 0.93), and Cu (R2 = 0.90). It is concluded that portable chlorophyll meter is a quick, reliable, and nondestructive tool for assessing DMY and nutrients affecting leaf greenness in wheat. However, further investigation in field conditions is recommended.

The use of hand-held chlorophyll meters as a tool to assess the nitrogen status and to guide nitrogen fertilization of potato crop

Fifteen experiments were carried out in different sites of Italy, Belgium, Scotland and The Netherlands from 1995 to 1999 to study the possible use of chlorophyll meter to assess the nitrogen status and to guide nitrogen fertilization of the potato crop. The results are gathered here and reviewed together with available information in literature. The paper deals with measuring principles of chlorophyll meter; relation between chlorophyll meter readings and analytical measurements of chlorophyll, analytical measurements of nitrogen, crop nitrogen content, tuber yield, and physiological processes in leaves; variations in chlorophyll meter readings related to nitrogen supply, potato cultivar, crop management, and sampling methods; use of chlorophyll meter readings for decision making in the management of supplemental nitrogen fertilization (assessment of chlorophyll meter critical threshold, plant response to addition of supplementary N).

THE USE OF SPAD-502 CHLOROPHYLL METER FOR DYNAMICALLY OPTIMIZING THE NITROGEN SUPPLY IN POTATO CROP: A METHODOLOGICAL APPROACH

The management of N fertilization through a method called “dynamic optimization of nitrogen supply” requires the assessment of crop nitrogen status throughout the growing season. A tool for plant analysis, that increased interest recently, is the hand-held chlorophyll meter SPAD-502 (Minolta - Japan), which allows leaf nitrogen status from measurements of chlorophyll content in potato. The data from this instrument is necessary to calculate some threshold values below which N supply is necessary to avoid yield losses. A procedure for the calculation of chlorophyll meter threshold value was set using data obtained in a potato trial conducted in 1997 at the Experimental Farm of the University of Padova at Legnaro, Italy. The trial was included in a long-term experiment on nitrogen fertilization conducted on different soil types. The experiment was conducted on 108 vegetation boxes of 4 m2 area (2x2 m) and 0.8 m depth. A randomized complete block design was used with three replicates of six increasing rates of N (0, 50, 100, 200, 300, 400 kg ha-1) factorially combined with 3 soil types (clay, silty-loamy, sandy), in either the presence or absence of residues of the previous crop (wheat straws). Linear-plateau equations were developed for calculating the relationships between SPAD values and yield and this equation allowed the calculation of STV (SPAD Threshold Value) which represents the limit below which a reduction in yield occurs. The procedure described in this work appears to be suitable for supplementary N management in potato crop. It can be used very easily for decision making on time and rate of supplementary N to potato.

COMPARISON OF SATELLITE AND AERIAL IMAGERY FOR DETECTING LEAF CHLOROPHYLL CONTENT IN CORN

Inseason sitespecific nitrogen application has the potential to improve the efficiency of nitrogen use and reduceenvironmental contamination. Identification of withinfield crop nitrogen stress is essential for improved nitrogenmanagement. Corn nitrogen stress is frequently associated with leaf chlorophyll content, which can be characterized byspectral reflectance measurements. Therefore, satellite remote sensing has potential for characterizing corn nitrogendeficiency on a wholefield scale. To evaluate the use of satellite imagery to detect nitrogen deficiency in corn during thegrowing season, this study compared spectral variables extracted from SPOT satellite imagery and digital aerial imagery,and investigated the relationship between spectral variables of the SPOT imagery and the measurement data of a handheldchlorophyll meter (or SPAD meter). SPOT images and aerial images were acquired on one commercial field in 1999 andanother one in 2000.<br><br>The correlation coefficient (r) between the NDVIs derived from the SPOT image and the aerial image was 0.73 in 1999,and 0.54 in 2000, respectively. When the field had large spatial variability in crop development in 1999, the spectral variablesfrom the SPOT image were strongly correlated with those from the aerial image. However, when the crop development wasmore uniform in 2000, the correlation between the SPOT image and the aerial image was not as good. The limited range ofavailable digital counts that can be used to represent the reflectance from an individual farm field for the SPOT system limitedits sensitivity in detecting crop stress. Nevertheless, the NDVIs from SPOT images were significantly correlated with SPADdata in both fields, with correlation coefficients of 0.90 in 1999 and 0.68 in 2000. The correlation between SPOT images andSPAD data was similar to that between aerial images and SPAD data, indicating that SPOT imagery may have potential fordetecting chlorophyll levels and nitrogen stress in corn during the growing season.

RELATIONSHIPS BETWEEN EXTRACTABLE CHLOROPHYLL AND SPAD VALUES IN MUSKMELON LEAVES

Chlorophyll content of muskmelon is usually determined by destructively sampling plant leaves. However, a hand-held SPAD-502 Chlorophyll Meter provides rapid and nondestructive measurements of leaf chlorophyll content. This study aims to determine the relationships between extractable chlorophyll and SPAD values in muskmelon leaves. SPAD readings were significantly related to extracted chlorophyll of muskmelon leaves both on a fresh weight and leaf area basis. Quadratic equations best described their relationships. At 10 days after nitrogen (N) fertilization, the r2 values for chlorophyll a, b, and total chlorophyll on a fresh weight basis were 0.84, 0.86, and 0.85, respectively, while on a leaf area basis, r2 values were 0.92, 0.95, and 0.94, respectively. At 17 days after fertilization, the r2 values for chlorophyll a, b, and total chlorophyll on a fresh weight basis were 0.57, 0.49, and 0.56, respectively, while on a leaf area basis, r2 were 0.72, 0.67, and 0.71, respectively. Therefore, the SPAD-502 Chlorophyll Meter can be used to measure chlorophyll content of muskmelon leaves.

Using a Chlorophyll Meter to Determine the Chlorophyll Concentration, Nitrogen Concentration, and Visual Quality of St. Augustinegrass

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 (r2 = 0.79), visual ratings (r2 = 0.74), and total Kjeldahl nitrogen (TKN) (r2 = 0.71). Readings taken from field-grown `Floratam', `Floratine', and `Floralawn' St. Augustinegrass were poorly correlated (r2 &lt; 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.

Effect of Sulfonylurea Herbicides on Field Corn Following an Application of Granular Insecticide at Planting, 1997

Abstract Field corn was ridge planted to a non-tilled seed bed near North Platte, NE, on 1 May. The soil in these plots was a Cozad silt loam. At the time of planting, soil moisture was adequate for germination and the soil temperature at a depth of 5 cm was about 7° C. Granular soil insecticides were applied in a 7-inch T-band at planting to 10 X 40 ft plots with a Nobel box on a bicycle wheel-type applicator. Bicep II herbicide was applied at a rate of 0.375 lb (AI)/acre 14 days after planting. The sulfonylurea herbicides, Basis Gold 90DF and Accent 75 WDG, were applied with a backpack CO2-charged sprayer as separate treatments made over the whorl of V3-stage field corn plants on 23 Jun. The herbicides were applied in a total volume of 10 gpa, at 30 psi, through 11001 VPTT flat-fan nozzles. Crop oil concentrate, at a rate of 1% v/v, was added to all Basis Gold 90DF treatments. Valent X-77 was added, at a rate of 0.25% v/v, to the Accent 75 WDG treatment. Liquid nitrogen fertilizer (28-0-0) was added, at a rate of 0.25 lb/acre, to all herbicide treatments. Four repl ications of each treatment were arranged in a RCB design. The effect of the herbicides on plant survival, plant height, plant condition and leaf greenness was evaluated 7 and 14 DAT. Plant conditions considered to be related to the herbicide application included reduced height, yellowed leaves and/or twisted whorls. The severity of these conditions was evaluated on a 1 to 5 scale where 1 represented little damage and 5 represented severely damaged and stunted plants. The effect of the herbicides on leaf greenness was evaluated with a handheld chlorophyll meter. This meter records depth of green color in a dimension less value. The effect of the herbicides plus insecticide was compared with plots treated with Counter CR insecticide alone. Treatment means for each variable were analyzed with ANOVA and were separated with Fisher’s Protected Test of Least Significant Difference.

Maize Leaf Absorptance of Photosynthetically Active Radiation and Its Estimation Using a Chlorophyll Meter

Recent evidence suggests that chlorophyll fluorescence techniques can be used to determine photosynthetic rates of maize (Zea mays L.) leaves much more rapidly than is possible with conventional gas exchange methods. However, the accuracy of such measurements depends directly on the accuracy with which leaf absorptance of incident photons in the PAR (photosynthetically active radiation) region can be estimated. Our objectives were (i) to monitor changes leaf ahsorptance in a typical maize crop over the growing season, and (ii) to determine if absorptance of maize leaves could be accurately estimated with a SPAD 502 hand‐held chlorophyll meter (Minolta Corporation, Ramsey, NJ). Leaves from six leaf positions were harvested on eleven dates between 55 and 134 d after planting. An integrating sphere and field‐portable spectroradio meter were used to measure reflectance and transmittance of leaf tissue samples at 5‐nm intervals between 400 and 700 nm, and a SPAD value was also determined for each sample. Greening of young leaves was associated with decreases in both reflectance and transmittance in the middle wavelengths of the PAR region, while leaf senescence was associated with increases in both reflectance and transmittance, primarily in the longer wavelengths of the PAR region. Leaf absorptance of incident photons in the PAR region by healthy, fully expanded leaves ranged from approximately 0.88 to 0.91; much lower values were observed for young, chlorotic, or senescing leaves. Regression analysis revealed a strong relationship (r2 = 0.98) between leaf absorptance and SPAD value, suggesting that the SPAD meter could be used to provide a rapid estimate of leaf absorptance in the field.

Effect of Sulfonylurea Herbicides on Field Corn Following an Application of Granular Insecticide at Planting, 1995

Abstract Field corn was ridge-planted to a non-tilled seed bed on 19 May. The soil in these plots was a Cozad silt loam. At the time of planting, soil moisture was adequate for germination and the soil temperature at a depth of 5 cm was about 7°C. Granular soil insecticides were applied in a 7-inch T-band at planting to 10 X 40 ft plots with a bicycle wheel type applicator. Four replications of each treatment were arranged in a RCB design. Broadstrike + Dual herbicide was applied immediately prior to plant emergence on 2 Jun. Several sulfonylurea herbicides were applied as separate treatments over the whorl of V3 stage field corn plants on 23 Jun. All herbicide applications were made with a CO2-charged sprayer through 8001 flat fan nozzles at 30 psi, in a total volume of 19 gpa. The sprayer was carried on an all terrain vehicle which was driven at 2 mph. With the exception of the Broad-strike + Dual treatments, Valent X-77 was added to each herbicide treatment at a rate of 0.25% v/v. Nitrogen fertilizer (28-0-0) was added to the Accent treatments at a rate of 1 gpa, to the Beacon and Basis treatments at a rate of 0.5 gpa and to the Exceed treatments at a rate of 0.25 gpa. The effect of the herbicides on leaf chlorophyll was evaluated 7 DAT with a hand held chlorophyll meter. This meter records depth of green color in a dimensionless value. The effect of the herbicides on plant height and condition was evaluated 7, 14 and 28 DAT. Plant conditions considered to be related to the herbicide application included reduced height, yellowed leaves and/or twisted whorls. The severity of these conditions was evaluated on a 1 to 10 scale where 1 represented little damage and 10 represented severely damaged and stunted plants. The effect of the herbicides plus insecticide was compared with plots treated with insecticide alone.

Effects of atmospheric CO 2 enrichment on chlorophyll and nitrogen concentrations of sour orange tree leaves

Since 18 November 1987, eight sour orange ( Citrus aurantium L.) trees have been maintained under well watered and fertilized conditions within four clear-plastic-wall open-top enclosures, two of which have been continuously supplied with ambient air of approximately 400 μl l −1 CO 2 and two of which have been supplied with air enriched to approximately 700 μl l −1 CO 2. At weekly intervals throughout years 4–7 of this long-term experiment, we measured chlorophyll a contents of 60 leaves on each of the trees with a hand-held chlorophyll meter that was specifically calibrated for our study. At bi-monthly intervals, we also measured the areas, dry weights and nitrogen contents of 68 leaves from each tree. Expressed on a per-unit-leaf-area basis, leaves from the CO 2-enriched trees contained 4.8% less chlorophyll and nitrogen than leaves from the trees exposed to ambient air. Because of their greater leaf numbers, however, the CO 2-enriched trees contained 75% more total chlorophyll and nitrogen than the ambient-treatment trees; the total productivity of the CO 2-enriched trees was 175% greater. Consequently, although per-unit-leaf-area chlorophyll and nitrogen contents were slightly lowered by atmospheric CO 2 enrichment in our experiment, their use efficiencies were greatly enhanced.

Chlorophyll meter predicts nitrogen status of tall fescue

Abstract The nitrogen (N) status of a crop can be used to predict yield and supplemental N fertilizer requirements, and rapid techniques for evaluating the N status of crops are needed. A study was conducted to determine the feasibility of using a hand held chlorophyll meter (SPAD 502, Minolta Co. Ltd., Japan) to monitor N status of tall fescue (Festuca arundinacea Schreb.). Four diverse tall fescue genotypes were grown at three locations in Alabama and fertilized at four N‐rates from 0 to 336 kg ha‐1. A similar experiment was conducted in the greenhouse using soil from the same field sites. Chlorophyll meter readings (SPAD) were taken, and extractable chlorophyll content, tissue N concentration and dry matter yield were determined at harvest. SPAD, extractable chlorophyll content, tissue N concentration, and dry matter yield increased quadratically (0.67 < R2 < 0.99) with increasing N fertilization in both experiments. All genotypes responded similarly to applied N, with some differences in magnitude. Re...

Evaluation of Yellowing Intensity of Sugar Beet Leaves Infected with Rhizomania by Using a Handheld Chlorophyll Meter.

Evaluation of Yellowing Intensity of Sugar Beet Leaves Infected with Rhizomania by Using a Handheld Chlorophyll Meter.

FIELD CHLOROPHYLL AND PETIOLE SAP NITRATE INDICATE THE NITROGEN STATUS OF POTATO VARIETIES

We report field experiments, under N limiting conditions, where applied N was varied between 0 and 252 Kg/ha. Two varieties (Castile and Allegheny) were planted in 1990 and 3 varieties (Katahdin, Monona and Superior) were planted in 1991. A curvilinear tuber yield response to N rate was obtained both years for all varieties with maximum yields at about 168 Kg/ha of N. Weekly field measurements with a hand-held chlorophyll meter (Minolta SPAD 502) were highly correlated to yield, to fresh petiole sap nitrate, to dry petiole nitrate and to the total N of whole leaves, all of which were generally highly correlated to each other and markedly affected by applied N. As plants matured the chlorophyll readings, and concentrations of nitrate and N decreased. In general variety differences or variety × N rate interactions were not significant which encourages the use of such tests to avoid unnecessary N sidedressings.

Apple, Foliar Pest Trial, 1985

Abstract Two pyrethroids and an organophosphate combination were evaluated against an untreated control in an apple block at Steeles Tavern, containing four cultivars: 'Delicious', 'Golden Delicious', 'Stayman', and 'York'. Four, single-tree replicates were used in a randomized complete block design. Applications were made using a truck-mounted Swanson sprayer with a handgun attachment. Trees were sprayed to the drip point (ca. 1869 liters/ha (200 gal/A)). Spray dates were 7 May, 30 May, 3 Jul, 17 Jul, 2 Aug and 16 Aug. STLM was evaluated on 14 Aug by counting mines seen during a 3-min examination of a tree's foliage. WALH-damaged shoots per 20 shoots on each tree were counted on 17 Sep. Population densities of both of these insects were low. Mites were evaluated using a leaf-brushing machine and 20 leaves per replicate, on 24 Jun and 14 Aug. Chlorophyll content was determined on 23 Sep using a hand-held chlorophyll meter.