PSI PlantPen/N-Pen N 110, Инструкция по эксплуатации

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RINCIPLE OF MEASUREMENT
Based on reflectance measurement at 565 nm and 760 nm, the N-Pen calculates NDGI (normalized difference greeness index) and
predicts relative nitrogen content (N-content) in dry matter. As leaf structure specifically influences plant reflectance profile, N-content
quantification was calibrated for three separate crops: wheat, barley and corn.
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EAF OPTICAL PROPERTIES AND NITROGEN
The N-Pen assesses N amount by means of spectral reflectance and by the concept of a close link between chlorophyll content and N
content in soil and plants (Evans, 1983, 1989; Penuelas et al., 1994; Schlemmer et al., 2005). Since the presence of chlorophyll affects
reflectance properties of leaves, optical methods based on spectral reflectance have been suggested to detect chlorophyll concentration
(Yoder and Pettigrew-Crosby, 1995; Richardson et al., 2002; Gitelson et al., 2003).
Spectral reflectance is one of the optical methods widely used for indirect quantification of crop physiological status, which can be
influenced by various factors, such as plant nutrients or pathological status. Chlorophyll absorption spectrum contains two absorption
bands, one in the red and one in the blue region of visible spectrum (Fig. 2). Reflectance spectrum of green leaves roughly complements
the absorption spectrum (compare A and B in
Fig. 2), indicating that the presence of chlorophyll is critical for optical properties of leaves
(Thomas and Gausman, 1977; Gitelson Merzlyak, 1994).
Fig. 2 Absorption and reflectance specrtra (A) leaf pigment extract (B) reflectance of leaf surface.
To determine optimum wavelength for N-content prediction, several experimental plant groups with different levels of N nutrition were
examined by measurement of spectral reflectance (Klem 2008). The reflectance values at each wavelength along reflectance spectrum
were correlated with N-content in experimental plant grou
ps. Pearson’s correlation coefficient was used as a statistical measure of the
strength of linear relationship between the paired data (Fig. 3A). The highest correlation was found for reflectance in the ranges 530 –
630 nm and 700 – 720 nm (negative correllation) and in the NIR region 750 – 900 nm (positive correlation). Indices based on reflectance
in the green region (around 560 nm) were reported to be more sensitive to N and chlorophyll content (Gitelson et al. 1997) than indices
based on reflectance in chlorophyll absorption maxima (e.g. NDVI).
Normalized Difference Greenness Index (NDGI) is calculated from leaf reflectance at wavelength bands 565 nm and 760 nm (equation 1),
NDGI = (R760 – R565) / (R760 + R565) (Equation 1),