Light-emitting-diode (LED) phyto-installations for meristem plants

Introduction. In many countries, potatoes are called the “second bread”. When the potatoes are grown with the help of tubers, the likelihood of infecting it with viral, bacterial and fungal diseases is high, which significantly reduces the yield. Cultivation of planting material of potatoes using the method of tissue culture (meristem culture) results in obtaining a large amount of virus-free planting material in a short time. For example, in half a year, it is possible to obtain up to 20...40 thousand exact genetic copies of plants free from infections from one healthy meristem plant, and with a potato yield of 10 to 15 kg/m ² [1, 2, 3].

Analysis of the special literature shows that about 30% of all electric energy generated in the world is consumed by lighting installations. Therefore, efficient consumption of electric energy by each LED installation will lead to a tangible saving of electrical energy [4, 5].

The effective use of light energy in the protected cultivation (crop-growing in sheltered ground) depends on the spectral composition of the LED phyto-installations, the amount of illumination (irradiance), and the duration of the daily plant irradiation (photoperiod).

To increase the plant productivity in sheltered (protected) ground conditions, it is necessary to learn how to manage its photosynthetic activity. In the open ground, the process of photosynthesis is primarily affected by solar radiation, the temperature, the content of CO 2 in the air, availability of water, etc. In the sheltered (protected) ground, many parameters are controlled and maintained within the required limits. Taking into account the fact that up to 95% of the crop yields are generated from the assimilated PAR energy, it is necessary to ensure that the plants use the energy of this range from the LED phyto-installations as efficiently as possible. Given that a plant is an accumulative bio-object, i.e. its development depends on the accumulated dose of the spectral components of the RAR zone, it is necessary to scientifically substantiate the most effective radiation spectrum of LED phyto-installations for meristem potato, which allows obtaining the maximum output with minimum costs [ 6, 7, 8].

In the Udmurt Republic, the meristem-based seed farming of potato is carried out by the Udmurt Agricultural Scientific Research Institute, with LB 80-type luminescent lamps used in its meristem laboratories. The lamp bulbs have phosphor coating inside that does not allow changing the radiation spectrum. Therefore, in order to increase the productivity of meristem plants, it is necessary to create LED phyto-installations that are most effective in the spectrum, on the basis of new scientifically grounded developments, which allow increasing the yield of products and reducing energy costs [9,10].

Currently, the lighting engineering industry produces a wide range of LED phytoinstallations with the possibility of changing the spectral composition, but only manually. The plant performance is primarily affected by the doses of the spectral components of the PAR zone. By using programmable logic controllers (PLCs), one can control the operation of differently colored LEDs in LED phyto-installations and obtain not only the required dose of the spectral components of the PAR zone, but also to adjust it in order to obtain the greatest output with reduced costs [11, 12, 13].

The research was carried out for ten years in accordance with the branch scientific and technical program No. 01201350385 “Research and development of electrical technologies at agro-industry enterprises”.

The goal of the work is to increase the efficiency of LED phyto-installations for meristem-based potatoes due to the scientific substantiation of the most effective doses of the spectral components of the PAR zone, which allow increasing the yield of healthy meristem potato and reducing the electricity consumption for its cultivation.

To achieve this goal, the following research objectives were set:

• 1.    Analyse the domestic and foreign literature on the use of LED phyto-installations in sheltered ground, where the possibility of changing the dose of spectral components of the photosynthetic active radiation (PAR) zone when growing plants in sheltered (protected) ground is realized.

• 2.    Obtain a mathematical model on the effect of the dose of spectral components of the PAR zone on the meristem potato performance.

• 3.    Develop the methodology to determine the doses of spectral components of the PAR zone for solar radiation.

• 4.    Develop an algorithm for the operation of a programmable logic controller for LED phyto-installations, which allows simulating the most effective radiation spectrum.

• 5.    Conduct laboratory and production tests and perform a feasibility study of the application of LED phyto-installations for the cultivation of meristem potatoes.

• ⁸⁰                  Агротехника и энергообеспечение. – 2021. – № 1 (30)

The spread of vegetable plants from one regions of the globe to others was due to human activities. By adapting to new conditions, plants acquired new properties that their ancestors did not have. Biologists believe that plants still retain their biological properties, which they acquired in the places of their original growth and cultivation (in the genetic homeland). Therefore, in order to increase the performance of vegetable crops, it is necessary to create conditions close to the historical homeland of this culture in order to obtain its greatest performance. For the first time they started cultivating potatoes all year-round in the subtropics and tropics: in such countries as Peru, Ecuador, Bolivia, where even now they get up to 4 potato harvests a year. Therefore, to obtain high plant performance, it is necessary to model the spectral composition of the PAR zone of the genetic homeland of potatoes [14, 15, 116]. Taking into account that the plant is an accumulative object, its development is greatly influenced by the doses of radiation in the PAR zone (N PAR ).

To calculate N PAR , a methodology was developed for calculating the intensity and duration of exposure of individual components of the PAR zone of solar radiation. Based on the obtained data, the time of exposure of each spectral component of the PAR zone was found, and the dynamic pattern of the spectral composition of solar radiation was determined for Peru and Krasnodar, taken for comparison as the main breadbasket of Russia [17, 18,19].

The methodology was proposed for calculating the dose of spectral components of the PAR zone of solar radiation. To do this, using the MS Excel package, we have obtained mathematical dependencies that describe the variation of each component of the solar radiation spectrum in the spring and summer periods for Peru and Krasnodar.

A profound analysis of the changes in the solar radiation spectrum components with a change in the sun's height from 0 ^o to 90 ^o was made by Professor A. Kleshnin [1]. In Krasnodar, in March the maximum sun angle (solar altitude) is 40 ^o , while in May – 60 ^o . In Peru, in March and May the maximum sun angle (solar altitude) is 80 ^o . The calculations data is presented in Tables 1, 2 [1].

Table 1 - Results of calculating the doses of the spectral components of solar radiation for Krasnodar during the growing season, in conventional units

Month	Violet 400…440 nm	Blue 440…490 nm	Green 490…565 nm	Yellow 565…595 nm	Red 595…760 nm	UV 295…400 nm	Total
March	82.0	197.5	209.0	268.5	423.5	79.5	1 260.0
April	103	223	288	272.5	456.5	78.5	1 421.5
May	130	262.5	266.5	352.5	493.5	95.5	1 600.5
June	166.5	300	346.5	407.5	569.5	115	1 905.0
July	157	314.5	335.5	412	583.5	121.5	1 924.0
August	146	341	389.5	392.5	564.5	124	1 957.5
Total	784.5	1 638.5	1 835.0	2 105.5	3 091.0	614.0	10 068.5
in %	7.79%	16.27%	18.23%	20.91%	30.70%	6.10%	100.00%

Analysis of Table 1 shows that the doses of PAR zones vary considerably by months. If we prioritize the radiation, most of the mean value of the radiation falls on red (31%), then yellow (21%), green (18%), blue (16%), violet (8%) and UV (6%). At the same time, the qualitative composition of the radiation varies considerably by months.

Table 2 - Results of calculating the doses of spectral components of solar radiation for Lima - the capital of Peru - by months, in conventional units

Month	Violet 400…440 nm	Blue 440…490 nm	Green 490…565 nm	Yellow 565…595 nm	Red 595…760 nm	UV 295…400 nm	Total
March	132.0	265.0	205.8	340.5	463.0	110.5	1 516.8
April	130.5	251.85	279.5	340	450.5	106	1 558.4
May	133.5	238	284	326	443	102	1 526.5
June	142	240.5	304.5	325.5	434.5	100.5	1 547.5
July	142	240.5	284.5	325.5	434.5	100.5	1 527.5
August	129	237.5	284.5	321.5	436.5	100.5	1 509.5
Total	809.0	1 473.4	1 642.8	1 979.0	2 662.0	620.0	9 186.1
in %	8.81%	16.04%	17.88%	21.54%	28.98%	6.75%	100%

Analysis of Table 2 shows that there is no significant difference in the doses of PAR zone by months. If we prioritize the radiation, then most of the radiation falls on red (29%), then yellow (22%), green (18%), blue (16%), violet (9%) and UV (6%), but when compared with Table 1, it can be seen that the qualitative composition of the radiation is different.

The conducted research showed that the changes in the doses of spectral components for Krasnodar and Peru (Tables 1, 2) can be reasonably modelled using Pearl-Reed curve in the wavelength range 360 ... 460 nm, and in the wavelength range 460 ... 760 nm the poly-nominal dependence can be used.

Changes in the doses of spectral components for Krasnodar and Peru (Tables 1, 2) can give a reasonable accuracy for modelling the logistic curve within the wavelength range of 360...460 nm (Table 3). In the subsequent range of wavelengths from 460 to 760 nm, the change in doses is described with sufficient accuracy by the polynominal dependence found using the trend line.

Table 3 - Data for calculating the logistic curve of average annual radiation doses in the wavelength range from 360 to 460 nm for Peru

x	`x 2	y	`a 1 /y	`(a 1 /y)-1	`lg((a1/y)-1)=z	xz	y`	(y`-y) 2
460	2E+05	270	1.02593	0.0259	-1.5863	-729.6822	272	4
450	2E+05	262.5	1.05524	0.0552	-1.2578	-565.9926	265	6.25
440	2E+05	252.25	1.09812	0.0981	-1.0083	-443.6326	255	7.5625
430	2E+05	230	1.20435	0.2043	-0.6896	-296.5409	240	100
420	2E+05	211.5	1.30969	0.3097	-0.5091	-213.8090	210	2.25
410	2E+05	184	1.50543	0.5054	-0.2963	-121.4973	180	16
400	2E+05	153.85	1.80045	0.8005	-0.0967	-38.6652	150	14.8225
390	2E+05	144	1.92361	0.9236	-0.0345	-13.4592	130	196
380	1E+05	127.5	2.17255	1.1725	0.0691	26.2698	120	56.25
370	1E+05	110	2.51818	1.5182	0.1813	67.0898	110	0
360	1E+05	103.35	2.68021	1.6802	0.2254	81.1312	106	7.0225
4050	2E+06				-3.4164	-1519.10		406.1575

Research Methods

While carrying out the scientific work, analytical and experimental research methods were used, mathematical modelling methods were applied using MS Excel software, theoretical bases of lighting engineering, electrical engineering, theory of regression analysis and mathematical statistics, methods of applied economics, and modern measuring equipment.

The validity of the research findings is verified by the agreement of the calculations results based on methods proposed by the authors, with the experimental data obtained during the testing of LED phyto-installations, positive results with the use of these phyto-installations in practice, as confirmed by the Acts on the implementation of scientific research results and Test reports.

We have been developing the LED installations for meristem plants since 2009 [10, 12, 13, 14, 17, 18, 19, 20]. According to the cultivation technology, meristem plants grow for 30 days.

Realization of the spectral composition of the historical homeland of the potato - the state of Peru, and the breadbasket of Russia – Krasnodar, was carried out using programmable logic controllers (PLCs) by the Russian company ‘Oven’ and German company ‘Schneider Electric’.

The program for Peru provides the operation of LED phyto-installations for 30 days, 16 hours a day, with a change in spectral composition during the day, depending on the sun angle, as it occurs under natural conditions (Fig. 4) [1, 15, 16]. The program for Krasnodar (Fig. 2) operates for 16 hours a day, according to the following algorithm: for 10 days the spectrum of March is simulated, the following 10 days - the spectrum of April, and the last 10 days - the spectrum of May. The program allows to change the spectral composition of radiation during the day.

In case of insufficient natural illumination (E<4 kilo lux), the program automatically turns the phyto-installations on, which allows maintaining the necessary illumination in the evening and in the morning.

For the PLC by ‘Oven” company, a program software written in the FBD language has been developed to control the operation of a single-colour LED using the instrumental software package of industrial automation “CoDeSys”, which contains data on change of the spectral composition for Peru and southern Russia - Krasnodar [1, 5, 10].

The developed configurations of the smart LED installation control system on the basis of the PLC allow simulating the spectral composition of radiation for any particular area during the day and for the required months [16, 17, 18].

Research Findings

The experiments were carried out in the meristem laboratory of the Federal State Budget Research Institution (FSBRI) Udmurt Agricultural Scientific Research Institute from 2009 to 2019.

In the experiments three options were compared:

• 1.    A 24-watt LED phyto-installation that simulates the spectral composition of radiation in the historical homeland of potato - Peru, i.e., the ratio of red, yellow, green, blue and violet emissions is 29%/22%/17%/16%/9%. We called it the “Peru Scheme”.

• 2.    A 24-watt LED phyto-installation that simulates the spectral composition of radiation of the main breadbasket of Russia - Krasnodar, i.e. the ratio of red, yellow, green, blue and violet emissions is 30%/19%/15%/13%/7%. We called it the “Krasnodar Scheme”.

• 3.    Luminaires with 80 W fluorescent lamps (control).

Tables 4 and 5 present the results of the research [1, 18].

Table 4 - Results of the experiments held on irradiation of meristem potatoes with LED installations

Source of radiation	Irradiation, kilolux	Number of meristem plants, pcs	Average height of plants, cm	Number of roots, pcs
LB 80 lamps (control)	4.0±0.2	60	9.2±0.4	31±2
Blue LEDs	1.9±0.15	60	8.5±0.5	30±1.5
White LEDs (22 Kd)	3.2±0.18	60	9.0±0.3	30±2
White LEDs (70 Kd)	4.5±0.21	60	9.4±0.4	31±2

Findings of the study show that the use of light-emitting diodes allows improving the biometric indicators of meristem plants and contributes to significant savings in electricity by 40...50%. Analysis of the change in the assimilating leaf area showed that the largest leaf area was found when plants were grown under a LED phyto-installation according to the Peru scheme.

Table 5 - Test results on irradiation of meristem potatoes

Plant characteristics	Irradiation method
	Peru Scheme	Krasnodar Scheme	LB 80 (control)
Stalk length, cm	4,8	4.9	5.1
Number of leaves, pcs.	7.5	7.45	5.57
Degree of development of the root system, in points	2.7	2.7	2.06

Analysis of the data shows that the highest plant performance was found when using a phyto-installation according to the Peru scheme.

The feasibility study of the effectiveness of the application of LED phyto-installations for the cultivation of meristem potatoes was carried out using net present value method. Two options were compared: LED phyto-installations following the Peru scheme, and actually used LB 80 lamps (control). Calculations showed that the application of the proposed LED phytoinstallation simulating the spectrum in Peru allows reducing the period of readiness of meristem potato plants for 4 days and, as a result, receiving about 15% more plants a year, compared with the control. The expected economic effect is about 76 thousand roubles, and income from the saved energy is 148 thousand roubles, with a payback period of LED phyto-installations of about 4 years.

Conclusions

• 1.    Taking into account the fact that the plant is an accumulative object, that is, its performance depends on the dose of the PAR zone, we proposed a mathematical model describing the effect of the dose of spectral components of the PAR zone radiation on the meristem potato performance, which demonstrated that simulation of the radiation spectrum of Peru allows to reduce the time of growing meristem potatoes for 4 days and to reduce the cultivation costs per one plant by 1.3 times.

• 2.    The simulation of the doses of spectral components of the PAR zone was carried out using the PLC, for which special control programs were developed that allow simulating the spectrum of solar radiation of the PAR zone in any geographical area and allow switching on the

• 3.    The experiments on the effect of the doses of spectral components of the PAR zone on the growth and development of meristem potatoes were carried out in the meristem laboratory of the Agricultural Scientific Research Institute from 2010 to 2019. The studies showed that the installation simulating the spectrum of Peru, the use of which allows to reduce specific electricity consumption by 50% and to increase the plant performance by 12...15%, is the most effective for meristem potato.

• 4.    Calculation of economic efficiency showed that the expected economic effect is about 76 thousand rubles, while income from the saved energy is 148 thousand rubles, with a payback period of about 4 years.

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LEDs automatically, depending on the time of day (sun angle) as well as on changes in plant illumination during the day.

Acknowledgements

The authors of the article express their deep gratitude to the scientists in the field of electrification of agricultural production and agricultural lighting equipment: R. Butenko, L. Prishchep, I. Borodin, D. Strebkov, N. Protasova, I. Sventitskiy, A. Liamtsov, A. Bashilov, S. Rastimehin, Yu. Zhilinskiy, V. Leman, G. Sarychev, A. Tikhomirov, A. Primak, V. Karpov, V. Sharupich, S. Ovchukova, L. Alferova, N. Kozhevnikova, V. Kozinskiy, O. Kositsyn, R. McCree, P. Mekkel, B. Singh, M. Fischer, J. Bonnet, P. Harris, who made an invaluable contribution to the development of this field and proved the effectiveness of the application of optical radiation for obtaining additional crop output, by having solved a number of theoretical and experimental tasks in the field of application and creation of radiation sources for agricultural enterprises and biological research.