УДК 633.11:581.132:631.5:57.081.1


V.P. Yakushev, E.V. Kanash, Yu.A. Osipov, V.V. Yakushev, P.V. Lekomtsev, V.V. Voropaev

In practical field experiment the influence of mineral nutrition deficit was determined during different agrotechnologies on optical characteristics of leaves and vegetable layer of summer wheat of the Leningradskaya 97 variety. It was shown, that the use of accurate agriculture promote to a forming of the most effective photosynthetic apparatus and high productivity of sowing. The distant measurements of sowing on colorimetric parameters of digital pictures permit to control a spatial heterogeneity of physiological state of sowing.

Key words: physiological state of crops, precision farming, reflection indices, colorimetric characteristics of canopy.


Precision farming is the form of agriculture intensification and landscape adaptation technologies, which allows to predict productivity, to identify crop responsiveness to fertilizers, to assess feasibility and completeness of farming activities in respect to specific environmental conditions (1). Optimization of agriculture and its adaptation to adverse climatic conditions require the use of modern contact and remote methods for monitoring crops’ physiological status. Non-destructive methods for diagnosing plant tissues are used in agriculture for more than three decades, but they still provide low resolution and require high economic costs. In this regard, the remote sensing of plant health for decision-making to optimize the production process can be performed by promising methods based on recording spectral characteristics of visible and near infrared range radiation reflected from plant leaves.

Photosynthesis in crops is a complex hierarchical process, which makes convenient distinguishing its indicators of capacity and intensity (efficiency). It has been reported in available literature, that diagnostics of crop condition usually focuses on plants ability to absorb light energy, with no considering the efficiency of its conversion in photochemical photosynthesis processes (2).

It is clear, that light absorption depends on the total area of assimilating leaf area per unit of soil surface (LAI - leaf area index ) and the content of photosynthetic pigments. The main requirement to reflection indices for evaluation LAI - maximizing of spectral contribution from green plants while minimizing the impact on this index from radiation reflected by soil. Sunlight reflection from soil monotonically increases in the range of visible - near infrared radiation (IR) (3, 4), whereas the reflectance spectra of plants show peaks in visible and near infrared regions with a minimum in red region due to its absorption by chlorophyll. All these facts make possible to assess plants growth applying simple indices, which are determined as a simple ratio of reflectance in two spectral regions, or the difference of reflection between them (5, 6). The most widely used index for estimation LAI is NDVI (normalized difference vegetation index):  NDVI = (NIR  RED) / (NIR + RED), where NIR and RED - a reflection, respectively at 750 and 680 nm (7). Though, identification of crops LAI is possible only in early ontogeny stages when the canopy is not closed yet.

Estimating the amount of radiation the red and near infrared regions reflected from a canopy allows identifying the proportion of radiation reflected by plants, which correlates with the quantity of absorbed photoactive radiation (PAR) and is a measure of photosynthetic system capacity. The deficit of nutrients, water and effects of other stressors do not limit plant growth, but there’s a close relationship between net productivity and absorption of solar radiation by sowings. In this case, it becomes possible to forecast net productivity with high accuracy upon the values of spectral indices, such as NDVI. However, in adverse environmental conditions, none of the commonly accepted spectral indices for estimation LAI can help distinguishing of more developed, but subjected to stress sowing from the less developed but rapidly growing one.

The diagnosis of photosynthetic apparatus activity based upon the assessment of chlorophyll content can’t always be considered as a certain indicator for objective estimation of plant physiological status. For example, have studied the response of wheat and barley to ultraviolet radiation (280-380 nm), it has been found that the relationship between chlorophyll reflection index and net productivity occurs only at the significant inhibition of plants growth (8). A small chlorophyll loss can be the defensive reaction aimed at creating conditions for eliminating the effects of oxidative stress, and not always accompanied with growth inhibition (9).

The purpose of our study was to compare optical characteristics of leaves and canopy, to identify the criteria for diagnostics of early stages of mineral nutrition deficiency and to study its effect on wheat photosynthetic apparatus against the background of different agricultural technologies including precision farming.

Methods. Experiments were performed in 2007 in the Leningrad region (the conditions of industrial experiment were described in detail previously) (1). The area of plots for variants - 2 ha in 2-fold repetition. The fertilizers: ammonium nitrate, grade B (JSC "Azot", Russia), azofoska (N:P:K = 16:16:16) (JSC "Ammofos", Russia), and potassium chloride (JSK “Uralkalij”, Russia) were introduced before sowing. The combination of fertilizers provided the necessary dose of nitrogen, phosphorus and potassium. Plants of spring wheat the variety Leningradskaya 97 were grown at four agricultural technologies applied: an extensive (C - control, I variant) – without using any fertilizers and protective preparations, normal (II variant) – fertilizers were introduced before sowing at a dose N50P50K50 (kg active ingredient/ ha), plants were treated with herbicide Lintur once at a dose of 135 g / ha (JSC “Bryansk Agro”, Russia), highly-intensive (III variant) - the fertilizer N110P70K110 was introduced before planting, plants were treated with herbicide Lintur (135 g/ha) and fungicide Falcon (“JSC Bryansk”, Russia), insecticide Karate Zenon («Syngenta», Switzerland) at a dose of 600 g/ha, growth regulator Tce Tce Tce («BASF», Germany) at a dose of 3 l/ha, and the additional dressing with water-soluble nitrogen fertilizer Poly feed («Haifa Chemicals», Israel) applied when tillering – booting phase (3 kg/ha) and earing – flowering (5 kg/ha), the highly-intensive with elements of precision farming (IV variant ) – pre-sowing fertilization was performed considering the spatial inhomogeneity of mineral nutrients distribution N70+dP70K70+d (d - dose of fertilizer, introduced into soil according the map of nutrients distribution). In the IV-th version, the nitrogen fertilizer was applied at phases of tillering - booting and earing-flowering considering crops condition determined by contact and remote sensors from the change in optical characteristics of leaves and canopy; the application of herbicides, fungicides, insecticides and growth regulators – the same as in variant III.

Spectral characteristics of plants were determined at phases of tillering and earing-flowering. The reflectance spectra of leaves were recorded in situ using the miniature spectra-radiometric fiber-optic system («Ocean Optics», USA), providing an optical resolution of 0,065-nm range from 400 to 1100 nm with a step of 0,300 nm, and software OOIBase32. 30 plants of each variant were selected to record reflectance spectra (replication of the experiment - 2-fold).

Studying colorimetric characteristics of leaves was performed using the same spectra-radiometric fiber-optic system and IRRAD-COLOR software, which allowed to determine a color hue, saturation and brightness as a three-dimensional model of color representation CIE (Commission Internationale de l'Eclairage) L*a*b* . In accordance with this model, L varies from 0 (black) to 100 (white) and characterizes color brightness, the axis a is a color change from red to green, along the axis b - from blue to yellow. Axes a and b overlap and represent diameters of circles along the perimeter of which color tone changes, and color saturation changes along its radius. Remote estimation of crops was performed using a radio-controlled aircraft device, equipped with GPS-navigation system and digital camera Olympus E-400 (1). The obtained aerial photography were treated with Photoshop CS3 using the model CIE L*a*b*. Statistical processing of data was performed using Excel XP and Statistica 6.0 software packages.

Results. Table 1 shows the calculated formula of reflectance index used to assess the physiological status of plants.

1.  Main reflectance indices characterizing physiological state of plants and detecting their oxidative stress

Reflectance index

Determined characteristic

Calculation formula



Chlorophyll content

(R750 - R705)/(R750 + R705 - 2R445)



The ratio of carotenoids  content and chlorophyll content

(R800 - R445)/(R800 - R680)



Photochemical activity of photosynthetic apparatus

(R570 - R531)/(R570 + R531)



Anthocyanins content

R750 (R550-1 - R700-1)



Light reflectance by a leaf



Note: In the calculation formulas of indices, R – reflectance at the appropriate wavelength.

Optical characteristics (reflectance indices ChlRI, ARI, PRI, and R800, see  description in Table 1) of leaves wheat the variety Leningradskaya 97 in phases of tillering (А) and earing-flowering (B) depending on cultivation technology: a, b, c and d – respectively, control, normal, highly-intensive technology and highly-intensive technology with elements of precision farming (see description in "Methods"). ChlRI, ARI and PRI values are presented in relative units, R800 - in percentage terms. Error bars - confidence interval at 95% level of significance (field experiment, the Leningrad region, 2007).









Optical characteristics of plants were closely associated with mineral nutrition regime and varied with plants oppression and inhibition of their growth. Pre-sowing fertilization promoted the expected raise of net plant productivity; already in tillering phase, net productivity in variants II (0,85 ± 0,03 g), III (0,99 ± 0,02 g) and IV (1, 14 ± 0,11 g) was, respectively, 24, 43 and 47% higher than in control (0,68 ± 0,05 g) (the values of biomass of 10 plants and the confidence interval at 95% significance level).

Despite the slight increase in ChlRI average values with increasing the dose of pre-sowing fertilizer (Fig.), it failed to identify any significant influence of mineral nutrition regime on this index. According to variance analysis, the effects of pre-sowing NPK doses on ChlRI variability in wheat leaves in tillering phase did not exceed 2% (p = 0.48). During this period, there was also no significant correlation between net productivity of plants and chlorophyll content (r=0,22).

The obtained results allow to conclude that in early stages of mineral nutrition deficiency, the intensity of photosynthesis and, consequently, a production process is not limited by small decrease in capacity of photosynthetic apparatus. Apparently, one of main causes for growth inhibition is reducing the efficiency of photosynthetic conversion of light energy into chemical substances. To diagnose the state of photosynthetic apparatus and study plants response to the deficit of basic nutrition elements, authors used different reflectance indices (see Table. 1) closely linked with plant resistance to oxidative stress and net productivity (13).

Photochemical reflectance index PRI was designed to assess the rate of change in relative content of xanthophyllous pigments - active regulators of luminous flux in pigment-protein complexes (14). When high-intensity light or under stressful conditions, the excessive light absorption with chlorophyll antenna complex is reduced due to the conversion of xanthophyllous carotenoids accompanied with heat release. Thermal dissipation of excessive energy is the most important photoprotection function of carotenoids aimed at protecting chloroplast photochemical system from irreversible damage due to the overflow in reaction centers with large amounts of energy which can’t be used. Carotenoids content was also estimated from SIPI (see Table. 1).

The value of R800 primarily depends on the volume of intercellular air space and the ratio of mesophyll surface area to leaf area; it is also connected with peculiarities in internal leaf structure, the length of  air-water interface, and the size of cells and organelles (10). Thus, the increase in R800 during a deficient mineral nutrition indicates the change in internal leaf structure providing the raise in light reflectance and decrease in proportion of absorbed solar radiation.

Anthocyanins, whose content in vegetative tissues was determined from the value of ARI, absorb solar radiation mainly in green and ultraviolet spectrum, to a very small degree - in the red region, and doesn’t absorb - in blue. Anthocyanins accumulation under stress condition reduces PhAR flow penetrating chloroplasts, which contributes to a stress-induced protection of reaction centers in the plastids (15).

2.  Net productivity of  wheat plants the variety Leningradskaya 97 in earing-flowering phase depending on mineral nutrition regime, by variants of the experiment (field experiment, the Leningrad region, 2007)


Part of a plant



young ears

whole plant









I (control)




































Note: variants description see in "Methods";  the table shows the values of biomass of 10 plants and a confidence interval at 95% significance level













The close correlation between the efficiency of photochemical processes and mineral nutrition regime was demonstrated by the variants of experiment in tillering phase - one of the earliest ontogeny stages. Under the deficit of nutrition, the content of substances partially inhibiting PhAR (ARI), was higher, and heat dissipation (PRI) raised as well as radiation reflectance caused by changes in leaf structure (R800) (see fig.). In tillering phase, the mineral nutrition effects contribution to ARI, PRI and R800 variability were equal to 13% (p = 2,5 × 10-4), 8% (p = 0.01) and 20% (p = 3,8 × 10-7), respectively.

In earing-flowering phase, the deficient mineral nutrition was manifested as a marked growth inhibition (Table 2) and change in spectral characteristics of plants due to the significant loss of chlorophyll against a background of accumulating anthocyanins and carotenoids (see fig.).

Depending on cultivation technology, the biomass of leaves in variants II, III and IV amounted to, respectively, 237, 273 and 385% of control. These data demonstrate the significant increase of assimilating leaf area in variants II, III and, particularly, in IV variant, in which fertilizers were applied considering spatial heterogeneity of nutrients content in soil and physiological state of plants, estimated by optical sensors and remote contact.

The decrease of culms biomass in variants II and III was observed at the simultaneous 30% increase in tillering. This fact suggest that culms of these plants contained less mechanical and conducting tissues, which increased possibility of their lodging. In version IV, the number of ear-bearing tillers in a single plant has grown by 80%, while their biomass was higher than in control.

In earing-flowering phase, all the variants demonstrated significantly different ChlRI values. The highest value  of ChlRI with the smallest definition error (0,54 ± 0,009) was found in variant IV with applying elements of precision farming. In variant II with normal fertilizer distribution,  ChlRI was smaller (0,51 ± 0,012). The considerably less chlorophyll content was found in leaves of variant II (ChlRI = 0,48 ± 0,013) and especially in control variant (ChlRI = 0,38 ± 0,018). In earing-flowering phase, the contribution of cultivation technology effects to ChlRI was equal to 65% (p=3,17 × 10-34).

Thus, the deficit of mineral nutrition has led to a sharp decrease in photosynthetic apparatus capacity during the second half of growing season, owing to the reduced area of assimilating leaf surface and decrease in chlorophyll content per unit of surface area.

3.  Colorimetric characteristics of leaves and canopy determined by contact and remote methods in wheat the variety Leningradskaya 97 in earing-flowering phase, depending on mineral nutrition regime (field experiment, the Leningrad region, 2007)


Contact sensor

Aerial photography







I (control)




























Note: variants description see in "Methods";  L*, a* и b*  - elements of color representation model CIE (Commission Internationale de l'Eclairage) (the table shows values and a confidence interval at 95% significance level).

At the same time, a deficient mineral nutrition caused significant decrease in efficiency of photochemical processes, which was indicated in control by higher values of PRI and ARI (see fig.). Cultivation technology effects on these indices exceeded 45% (p = 3,17 × 10-20).

Under poor mineral nutrition, the decrease in chlorophyll content with accumulation of anthocyanins and carotenoids was accompanied by a change in color of plants and canopy (Table 3).

In variant I (control), plants exhibited a pronounced chlorosis, in variant II - a slight decrease in color intensity,  while in III and IV, the same intense blue-green color of leaves was observed. It should be noted, that in variant I (control), due to the formation of smaller leaves and early death of lower leaves tiers, a sowing canopy remained open (not serried) even in earing-flowering phase. In variants III and IV (particularly in IV), their large intensely colored leaves and the greater number of tillers formed a serried canopy. The analysis of spectral characteristics of leaves and canopy revealed significant differences even between the visually similar variants (see Table. 3).

Spectral characteristics of leaves significantly varied in all the variants - in the control with acute deficit of mineral nutrition, in variants II-IV with improved conditions, and they were distinct even between variants III and IV depending on methods of applying fertilizers and nitrogen dressing (estimated by contact sensor - from a* and b*, when aerial photography -  from b*). The contribution of cultivation technology effects to values of the indices L* and a* was 40% , to b* - 50% (p = 6,5 × 10-17-2,7 × 10-19).

Fertilizer application according to a spatial heterogeneity of soil agrochemical characteristics and a condition of plants at different ontogeny stages promoted the increased yield: in variant IV, the yield was 25, 40 and 60% higher, respectively, than in variants II, III and I (control). It was interesting to compare the yield in variants III and IV. The differentiated application of mineral fertilizers and nitrogen fertilizing stimulated yield raise by 25%, while reducing the doses of potash and nitrogen fertilizers - by 64 and 70% compared to variant III.

Thus, the application of precision farming agriculture technologies (fertilization correlated with spatial heterogeneity of nutrients content in soil and physiological state of plants) promotes the formation of photosynthetic apparatus providing the better absorption and assimilation of solar energy by plants. At the deficient mineral nutrition, the index ChlRI decreases, while SIPI, PRI, ARI and R800 reflectance indices increase, thus reflecting loss in capacity and efficiency of photosynthetic apparatus. Consequently, worsening in physiological condition of a certain crop can be detected by the reduce in its ChlRI compared with the same index defined in optimal conditions. The raising indices SIPI, PRI, ARI and R800 can be used as a signal of photosynthetic apparatus suppression and growth inhibition by early or non-manifested stress exposure of nutritional deficit, as well as in early stages of the deficit when chlorophyll content remains unchanged (or it changes insignificantly). The methods of sowing remote estimation by spectral characteristics of plants depending on content in leaves of chlorophyll, carotenoids and other substances absorbing visible spectrum radiation, as well on sowing architectonics and the proportion of projective cover on soil, provide good resolution and allow identification of field areas with deficient mineral nutrition.



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Agrophysics Development and Research Institute, Russian Academy of Agricultural Sciences,
, St.Petersburg 195220, Russia
e-mail: office@agrophys.ru, ykanash@yandex.ru

Received February 17, 2009