Estimation Of Leaf Chlorophyll Content Research Articles

Physiological and Horticultural Effects of Sweet Cherry Chemical Blossom Thinners

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.

Parâmetros de planta para aprimorar o manejo da adubação nitrogenada de cobertura em milho

O milho é uma das culturas mais exigentes em fertilizantes nitrogenados os quais proporcionam os maiores acréscimos no rendimento de grãos. Para manter a planta bem nutrida, há necessidade de estimar corretamente a quantidade de nitrogênio (N) que deve ser aplicada no solo, com intuito de satisfazer as suas necessidades durante todo o ciclo. No Rio Grande do Sul e Santa Catarina, o teor de matéria orgânica, a expectativa de rendimento de grãos e a contribuição da cultura antecedente como fonte de N são os parâmetros que têm servido como critério para recomendação de adubação nitrogenada no milho. No entanto, considerando a complexidade da dinâmica do N no solo, e todas as modificações que ocorrem durante a ontogenia desta cultura, outros parâmetros podem ser úteis para auxiliar na decisão sobre o manejo da adubação nitrogenada em cobertura. Vários parâmetros de planta têm sido estudados como indicadores do nível de N no tecido. Dentre estes, destacam-se o teor de nitrato no colmo, o teor e o acúmulo de N na folha e/ou planta e o teor relativo de clorofila na folha. A estimativa do teor de clorofila na folha pelo clorofilômetro tem sido bastante estudada nos últimos anos, em função da sua rapidez, precisão e baixo custo. Esta revisão visa abordar parâmetros de planta que podem ser utilizados como indicadores do nível de N na planta para predizer a necessidade de adubação nitrogenada em cobertura na cultura do milho, objetivando aumentar a eficiência de uso do nutriente e reduzir o impacto ambiental do N aplicado.

Distortion of the SPAD 502 chlorophyll meter readings by changes in irradiance and leaf water status

- The SPAD 502 Chlorophyll Meter can estimate leaf chlorophyll content as a surrogate measure of the nitrogen (N) status of plants, and therefore, it can be used to assess the N requirements of crops. In this work, we show that irradiance, leaf water status and time of measurement (i.e., morning vs. afternoon), may interfere with the SPAD 502 measurements. SPAD values increased by 2-3 units as relative leaf water content decreased from 94 to 87.5 57492768n wheat leaves. A change in irradiance (from 1100 to 600-650 mmol m-2 s-1) caused an increase of about 2 SPAD units in potted maize plants. Throughout the day, SPAD values varied by up to 4 units in well-watered plants of maize growing under field conditions. The slope of the response of the SPAD meter to chlorophyll content was steeper in the morning than in the afternoon. Since the range of SPAD values that may separate N deficiency from N surplus in a crop are often relatively narrow, time of measurement, irradiance and plant water status must be taken into account to precisely monitor crop N needs with the SPAD 502.

Chlorophyll content in eucalypt vegetation at the leaf and canopy scales as derived from high resolution spectral data.

The physiological status of forest canopy foliage is influenced by a range of factors that affect leaf pigment content and function. Recently, several indices have been developed from remotely sensed data that attempt to provide robust estimates of leaf chlorophyll content. These indices have been developed from either hand-held spectroradiometer spectra or high spectral resolution (or hyperspectral) imagery. We determined if two previously published indices (Datt 1999), which were specifically developed to predict chlorophyll content in eucalypt vegetation by remote sensing at the leaf scale, can be extrapolated accurately to the canopy. We derived the two indices from hand-held spectroradiometer data of eucalypt leaves exhibiting a range of insect damage symptoms. We also derived the indices from spectra obtained from high spectral and spatial resolution Compact Airborne Spectrographic Imager 2 (CASI-2) imagery to determine if reasonable estimates at a scale of < 1 m can be achieved. One of the indices (R 850/R 710 index, where R is reflectance) derived from hand-held spectroradiometer data showed a moderate correlation with relative leaf chlorophyll content (r = 0.59, P < 0.05) for all dominant eucalypt species in the study area. The R (850)/R (710) index derived from CASI-2 imagery yielded slightly lower correlations over the entire data set (r = 0.42, P < 0.05), but correlations for individual species were high (r = 0.77, P < 0.05). A scaling analysis indicated that the R (850)/R (710) index was strongly affected by soil and water cover types when pixels were mixed, but appeared to be invariant to changes in proportions of understory, which may limit its application.

Integrated narrow-band vegetation indices for prediction of crop chlorophyll content for application to precision agriculture

Recent studies have demonstrated the usefulness of optical indices from hyperspectral remote sensing in the assessment of vegetation biophysical variables both in forestry and agriculture. Those indices are, however, the combined response to variations of several vegetation and environmental properties, such as Leaf Area Index (LAI), leaf chlorophyll content, canopy shadows, and background soil reflectance. Of particular significance to precision agriculture is chlorophyll content, an indicator of photosynthesis activity, which is related to the nitrogen concentration in green vegetation and serves as a measure of the crop response to nitrogen application. This paper presents a combined modeling and indices-based approach to predicting the crop chlorophyll content from remote sensing data while minimizing LAI (vegetation parameter) influence and underlying soil (background) effects. This combined method has been developed first using simulated data and followed by evaluation in terms of quantitative predictive capability using real hyperspectral airborne data. Simulations consisted of leaf and canopy reflectance modeling with PROSPECT and SAILH radiative transfer models. In this modeling study, we developed an index that integrates advantages of indices minimizing soil background effects and indices that are sensitive to chlorophyll concentration. Simulated data have shown that the proposed index Transformed Chlorophyll Absorption in Reflectance Index/Optimized Soil-Adjusted Vegetation Index (TCARI/OSAVI) is both very sensitive to chlorophyll content variations and very resistant to the variations of LAI and solar zenith angle. It was therefore possible to generate a predictive equation to estimate leaf chlorophyll content from the combined optical index derived from above-canopy reflectance. This relationship was evaluated by application to hyperspectral CASI imagery collected over corn crops in three experimental farms from Ontario and Quebec, Canada. The results presented here are from the L'Acadie, Quebec, Agriculture and Agri-Food Canada research site. Images of predicted leaf chlorophyll content were generated. Evaluation showed chlorophyll variability over crop plots with various levels of nitrogen, and revealed an excellent agreement with ground truth, with a correlation of r 2=.81 between estimated and field measured chlorophyll content data.

Field evaluation of the chlorophyll meter to predict yield and nitrogen concentration of switchgrass

Chlorophyll meters have been used to estimate leaf chlorophyll content, and therefore nitrogen (N) status and fertilization requirements for several crops. However, until now C4 forage grasses have not been investigated in this regard. A field study was conducted in 1995 and 1996 to evaluate the potential of chlorophyll (SPAD) meter readings to determine switchgrass N concentration and herbage yield. Meter readings were taken on the top most fully expanded leaves of switchgrass grown on a free draining sandy clay loam soil (St Bernard, Typic Hapludalf) fertilized at 0, 75, or 150 kg N ha‐1. The switchgrass was either cut at the end of the season or every four or six weeks. Herbage N concentration in uncut stands declined with time while SPAD readings increased to a mid‐season maximum, beyond which they declined rapidly. The relationship between N concentration and SPAD readings was linear (r2=0.62–0.93; p<0.01) for the cut systems. Exceptforthe 1st cut under the 4‐week harvest regime, there were positive correlations between dry matter yield and SPAD meter readings (r2=0.58–0.96; p<0.01). These results indicate that SPAD meter readings can be used to measure N concentration and/or monitor N availability for seed production, and when N is the limiting factor, to estimate yield of switchgrass (Panicum virgatum L.)

Non‐destructive Determination of Leaf Chlorophyll Content in Four Crop Species1

AbstractA recent non‐destructive technique allows estimation of leaf chlorophyll content using the portable SPAD‐502 chlorophyll meter. Measurements were taken on four species (winter wheat, maize, soyabean and tobacco) subjected to different nitrogen regimes or senescence status and the: non‐destructive readings were compared with analytical results obtained by solvent extraction. In general, the relationship between the SPAD measurement and the analytical result was not linear and species was a factor in three out of four crops. Linear, quadratic and exponential curve fitting are presented; only die interpolation with a polynomial exponential function adequately descries the whole data set. The presence of statistically non‐significant differences between the estimated values of wheat and maize on the one hand and significant: points of difference between those of tobacco and soyabean on the other suggests distinct behaviour patterns far monocots and cicots. This type of response maybe explained by differences, in the optical properties of pigments with differing sparial distributions (sieve effect) and therefore by in vivo and in vitro different procedures and the structural diversity of leaves belonging to the two subclasses.

Non-Destructive Determination of Chlorophyll Content of Leaves of a Green and an Aurea Mutant of Tobacco by Reflectance Measurements

Summary Reflectance spectra from 400 to 800 nm with a spectral resolution of 1 nm and the content of photosynthetic pigments were acquired for leaves of an aurea mutant and a green tobacco ( Nicotiana tabacum L.) covering a range of chlorophyll a content from 7 to 30.8 μ cm -2 and total chlorophyll a + b level from 8.4 to 41.4 μg cm -2 leaf area. At a chlorophyll a content of more than 7 μg cm -2 leaf area the reflectance near 670 to 680 nm was not sensitive to a variation in chlorophyll content due to saturation of the relationship ≪absorption vs. chlorophyll content≫. The wavelength position of the red reflectance minimum (Rmin) in the main red absorption bands of in vivo chlorophyll a proved to be independent of the chlorophyll content of leaves and thus is not suitable for chlorophyll determination. Maximum sensitivity of leaf reflectance to variation in chlorophyll content was, however, found in a wide spectral range from 530 to 630 nm and near 700 nm. The wavelength of the red edge position of the reflectance spectrum (inflection point IP) in the range of 694 to 706 nm correlated very closely with the leaves' chlorophyll content in a curvilinear manner. The Ip is also closely correlated in a linear manner with the reflectance signals at 550 and 700 nm. Reflectances near 700 nm and 550 nm were found to be sensitive indicators of the red edge position and the chlorophyll content of leaves as well. The ratios of reflectances in the near infra-red range of the spectrum (above 750 nm) to that at 700 nm and at 550 nm, R NiR /R700 (or R750/R700) and R nir /R550 (or R750/R550), were directly proportional (r 2 >0.93) to the leaves' chlorophyll content. These two novel indices for chlorophyll determination (R750/R700 and R750/R550) allowed the estimation of leaf chlorophyll content with an error of less than 2.1 μg cm -2 . The two new vegetation indices, R750/R700 and R750/R550, are linearily correlated to the chlorophyll content. They exhibit a more than 6 times wider dynamic range than the widely used Normalized Difference Vegetation Index NDVT. The new vegetation index ratios are very sensitive to changes in chlorophyll content at low, medium and high chlorophyll content which is not the case for the NDVI. This suggests the application of the new indices R750/R700 and R750/R550 in the near and remote sensing of the chlorophyll content of terrestrial vegetation.

A non‐destructive determination of leaf chlorophyll in Vitis vinifera

SummaryA portable leaf greenness meter (SPAD‐501) has been used to provide a rapid and non‐destructive measurement of leaf chlorophyll in Vitis vinifera. Leaf extracted chlorophyll was related linearly to SPAD readings. It is suggested that separate linear equations should be developed for each cultivar so as to maximise the accuracy of estimating leaf chlorophyll content as a function of SPAD readings.