Tony K. Yanev

Early detection of changes in leaf reflectance of pea plants (Pisum sativum L.) under herbicide action

Based on high resolution leaf spectral reflectance data a new technique was developed and applied to detect damages of agricultural plants under the action of low intensity stress factors (herbicides) which at very low concentrations could not be established by the standard biochemical and biometric techniques. Results are presented from a remote sensing study of the peculiarities of the leaf spectral reflectance of pea plants (Pisum salivum L.) treated with atrazine and 2.4-D (2.4 - phenoxyacetic acid) at three low concentrations (0.01 /spl mu/M, 0.1 /spl mu/M and 1 /spl mu/M, respectively 2.15, 21.5, and 215 /spl mu/g/l for atrazine and 2.59, 25.9, and 259 /spl mu/g/l for 2.4-D) as compared to the field dose of these herbicides commonly used in the agricultural practice. The physiological status of the plants was assessed using biometric and biochemical parameters such as length, fresh weight, dry weight and electrolyte leakage. The high-resolution spectral data were obtained using a multichannel spectrometer in the visible and near infrared ranges of the electromagnetic spectrum in 128 channels at a spectral resolution (halfwidth) of 2.6 nm. Using the technique which employs discriminant analysis and other statistical methods we established the presence of statistically significant differences in the arising variations of the leaf spectral reflectance characteristics between control and treated plants in the green (520+580 nm), red and near infrared (690+800 nm) ranges of the spectrum.

Effects of Salinity on Leaf Spectral Reflectance and Biochemical Parameters of Nitrogen Fixing Soybean Plants (Glycine max L.)

Measurements of physiology and hyperspectral leaf reflectance were used to detect salinity stress in nitrogen fixing soybean plants. Seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. Salinity was performed at the stage of 2nd–4th trifoliate expanded leaves by adding of NaCl in the nutrient solution of Helrigel in concentrations 40 mM and 80 mM. A comparative analysis was performed between the changes in the biochemical parameters ‐ stress markers (phenols, proline, malondialdehyde, thiol groups), chlorophyll a and b, hydrogen peroxide, and leaf spectral reflectance in the spectral range 450–850 nm. The spectral measurements were carried out by an USB2000 spectrometer. The reflectance data of the control and treated plants in the red, green, red‐edge and the near infrared ranges of the spectrum were subjected to statistical analysis. Statistically significant differences were found through the Student’s t‐criterion at the two NaCl concentrations in all of the ranges examined with the exception of the near infrared range at 40 mM NaCl concentration. Similar results were obtained through linear discriminant analysis. The tents of the phenols, malondialdehyde and chlorophyll a and b were found to decrease at both salinity treatments. In the spectral data this effect is manifested by decrease of the reflectance values in the green and red ranges. The contents of proline, hydrogen peroxide and thiol groups rose with the NaCl concentration increase. At 80 mM NaCl concentration the values of these markers showed a considerable increase giving evidence that the soybean plants were stressed in comparison with the control. This finding is in agreement with the results from the spectral reflectance analysis.Measurements of physiology and hyperspectral leaf reflectance were used to detect salinity stress in nitrogen fixing soybean plants. Seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. Salinity was performed at the stage of 2nd–4th trifoliate expanded leaves by adding of NaCl in the nutrient solution of Helrigel in concentrations 40 mM and 80 mM. A comparative analysis was performed between the changes in the biochemical parameters ‐ stress markers (phenols, proline, malondialdehyde, thiol groups), chlorophyll a and b, hydrogen peroxide, and leaf spectral reflectance in the spectral range 450–850 nm. The spectral measurements were carried out by an USB2000 spectrometer. The reflectance data of the control and treated plants in the red, green, red‐edge and the near infrared ranges of the spectrum were subjected to statistical analysis. Statistically significant differences were found through the Student’s t‐criterion at the two NaCl concentrations in all of the ranges examined...

Remote Sensing Study of the Influence of Herbicides Fluridone and Acifluorfen on the Spectral Reflectance of Pea Plant Leaves (Pisum sativum L.)

Results from a remote sensing study of the leave spectral reflectance of pea plants (Pisum sativum L. cultivar Scinado) treated by the photosynthetic herbicides fluridone and acifiuorfen are presented. According to the mode of action, fluridone belongs to Fl (photobleaching) group of herbicides, and acifiuorfen -to the group E as classified by the Herbicide Resistance Action Committee. The pea plants were grown hydroponically in a growth chamber in a nutritious medium to which the herbicides were added at two low concentrations (1 muM, 0.1 muM for fluridone, and 25 muM, 2.5 muM for acifiuorfen). The high-resolution spectral data were obtained in the visible and near infrared ranges of the spectrum (450/850 nm) using a USB2000 fiber optic spectrometer at a spectral resolution (halfwidth) of 1.5 nm. After data analysis, optimal spectral intervals for evaluation of the herbicide action were specified. The changes occurring in the spectral reflectance of the pea plants were assessed in four intervals: 520/580 nm (region of maximal reflectivity of green vegetation), 640/680 nm (region of maximal leave absorption), 690/720 nm (red edge region), and 720/770 nm (near infrared region) using the t-criterion of Student and linear discriminant analysis. Statistically significant differences were found between the spectral reflectance data of leaves of control and treated with herbicides plants at a significance level p<0.05 for the two fluridone concentrations and for 25 muM concentration of acifiuorfen. The applied approach provides fast and reliable remote sensing of plant response to the environment.

Effects of Salinity on Chlorophyll Fluorescence of Nitrogen Fixing Soybean Plants (Glycine max L.)

Leaf chlorophyll ffluorescence was measured in order to assess the effect of salinity on nitrogen fixing soybean plants. Three day’s seedlings were inoculated with suspension of Bradyrhizobium japonicum strain 273. The plants were grown at nutrient solution of Helrigel and salinyzed at stage of 2nd trifoliate expanded leaves by adding of NaCl at concentrations 40 mM and 80 mM. The chlorophyll fluorescence was registered by an USB2000 spectrometer in the spectral range 600–850 nm. As a source of actinic light a light emitting diode with the maximum of the light output at 470 nm was used. The course of the fluorescence spectra and the slow transient fluorescence kinetics were investigated. The Student’s t‐criterion and discriminant analysis were applied to estimate the changes between fluorescence spectra of control and treated soybean plants in five characteristic wavelengths in the spectral range 600–850 nm. Statistically significant differences were established by the t‐criterion at p<0.05 for data at th...

Use of a Remote Sensing Method to Estimate the Influence of Anthropogenic Factors on the Spectral Reflectance of Plant Species

Results from a remote sensing study of the influence of stress factors on the leaf spectral reflectance of wheat and tomato plants contaminated by viruses and pea plants treated with herbicides are presented and discussed. The changes arising in the spectral reflectance characteristics of control and treated plants are estimated through statistical methods as well as through derivative analysis to determine specific reflectance features in the red edge region.

Theoretical distributions of vegetation indices and their approximation by normal distributions

Abstract Numerous vegetation indices (VI), calculated from spectral reflectance factors (SRF) obtained by means of spectrometers, are widely used in remote sensing practice. Theoretical VI distributions (TVID) are necessary to utilize statistical techniques to estimate, through VIs, the significance of the impact of seasonal changes, fertilization, polluters etc. on the important parameters of vegetation, soil and other areas. In this paper the TVIDs of some of the most frequently used VIs are derived. These TVIDs are to be used for precise statistical inferences. It is shown that they are close enough to the normal distribution that the known statistical techniques developed for normally distributed random variables may be used in the cases of statistical estimations made at a usual significance level.