Innovative energy-saving technology of irradiation of seeds of coniferous trees

Introduction Conifers are a highly recommendable green-city solution, as they are every-green, lower-maintenance, longer-living compared to their deciduous counterparts and keep their decorative value year-round. Besides, it should be borne in mind that conifers retain 30 times as much dust as the aspen, 12 times as much as the birch, while their phytoncide production is double that of deciduous plants, botanists have found. Being ever-green, low-maintenance, longer-living, and able to keep their decorative value year round, conifers are a better green-city solution [1, 2, 3, 4, 5, 6].

In 2006, the Russian Federation adopted its Forest Code to implement such programs as Biodiversity of the Russian Forest (1995) and Russia's Forests (1997); the Code states specifically that only high-quality seeds must be used for reforestation.

While there are multiple various methods for activating the germination of seeds, we propose pre-sowing exposure to, or irradiation with, LED-generated ultraviolet (UV). Employing natural mechanisms only, this innovative energy-saving light electrotechnology is eco-friendly, costefficient, and harmless to human health.

Literature review and our earlier studies have shown that exposing agricultural-plant seeds to ultraviolet does have a positive outcome manifesting itself in increased germination, reduced seed consumption, and stronger seedlings [7]. These factors cumulatively result in a more sustainable yield of decorative plants and conifers used as a green-city solution.

The UV effects are not well-known with respect to the seeds of Thuja Occidentalis. That's why designing an eco-friendly LED unit for presowing UV irradiation of Thuja Occidentalis seeds is a relevant problem.

This research effort is aimed at designing an eco-friendly LED unit for pre-sowing UV irradiation of Thuja Occidentalis seeds to find and substantiate in a scientifically robust manner the most efficient UV dosage that could improve the germination of such seeds.

Materials and Methods . The Automated Electric-Drive Department of Izhevsk State Academy has spent over 10 years researching pre-sowing UV exposure of seeds [8]. They used environmentally hazardous mercury-vapor lamps as a UV source. In 2016, a small-size LED UV 50 x 40 x 40 mm unit was made, consisting of 54 low-power LEDs generation uniform radiation on the active surface. The total power of 54 UV LEDs was 2 W [9]. For comparison, earlier mercury-vapor UV lamps had a power of 24 to 400 W.

Based on the positive results obtained in 2017, we enhanced this unit by increasing the number of LEDs to 81. The new version had the following dimensions: 70 x 60 x 20 mm [10]. This was a 3-W unit. A TKA Radiometer instrument was used to measure the UV radiation power in

UVA, UVB, and UVC ranges. Table 1 presents the reasults of measurements.

Table 1 Range-specific UV measurements

UV radiation type	Spectral range	Radiation power
UVA	315..400 nm	3.5 W/m2
UVB	280..315 nm	0.087.5 W/m2
UVC	200..280 nm	0.013 W/m2

Data demonstrates that LED radiation is mostly within the UVA range.

Laboratory Test Results . In February 2018, we experimented with exposing Thuja Occidentalis seeds to the radiation of our improved LED UV unit [11].

Seeds had been provided by the Forestry Faculty of the Federal State Educational Institution of Higher Education Izhevsk State Agricultural Academy. Germination was rated per GOST 13056.6-97 Seed of Trees and Shrubs. Methods for Determination of Germination.

For analysis, a medium-size sample was taken from each batch, and 100 seeds were randomly selected in each sample. Seed germination was carried out at 20°С in Petri dishes on a bed of filter paper imbued with distilled water and treated with a potassium-permanganate solution. Qualitative indicators of germination rate were measured on the 7th day, while the germination and length of seedling roots produced from exposed seeds were measured on the 20th day as stipulated by the GOST.

Seeds were exposed to three different UV doses; there also was a control sample consisting of non-exposed seeds, see Table 2.

Table 2 UV exposure of Thuja Occidentalis seeds

Sample	Dose, kJ/m2	Exposure time, min
Control	0	0
1	2	9.5
2	3	14.3
3	4	19

The dose (H, kJ/m2) was found as follows:

Н = Е •t, where Е is the radiation power, W/m²; t is the exposure time, s

Table 3 presents the experiment results.

Table 3 Changes in the germination of exposed seeds

Sample	Dose, kJ/m2	Germinated successfully, %	Did not germinate, %	Germination vs the control sample, %
Control	0	78	22	100
1	2	90	10	112.8
2	3	84	16	107.6
3	4	80	20	105.1

As can be seen from Table 3, Thuja Occidentalis seeds germination rate was 12.8% higher when exposed to 2 kJ/m² UV light as compared to non-exposed controls, making for a faster germination and production of earlier and stronger seedlings.

Studies have therefore shown that UV exposure of seeds does improve the germination rate, the germination, and the length of seedlings. This means better seed-sowing quality and stimulates further growth of the planted material. Using an LED UV unit for seed irradiation is an innovative, cost-efficient, eco-friendly, electrically safe, and efficient method that saves 70...80% power compared to the earlier solution, i.e. mercury-vapor lamps.

Conclusions

Studies have shown that exposing Thuja Occidentalis seeds to UV radiation is a promising way to stimulate seed germination. At the same time, this method is not only more cost-efficient compared to conventional chemical stimulation, but also eco-friendlier thanks to zero soil contamination.

In terms of technical- and cost-efficiency, using UV LED units have been proven to have 80...90% lower power consumption compared to earlier DRT-400 mercury lamps. UV LED units have been estimated to pay off in approximately four months.

Obolensky3