The Effect of Colour Plastic Films on the Growth

The Effect of Colour Plastic Films on the Growth

The Effect of Colour Plastic Films on the Growth, Yield and Plant Pigment Content of Tomatoes

In this article, the effect of using polyethylene films with different colors on the growth and development of tomato plants is investigated compared to the colorless control sample.

The growth of the tomato plant primarily depends on the amount and wavelength of the received light and the temperature. (1)  Both factors and their interaction can affect plant growth and development.  (2 and 3)

Today, the selective filtration of the spectrum of natural sunlight to control the growth of plants and ornamental vegetables is mainly done by using colored covers of greenhouse films.

Different lights with different wavelengths during cultivation affect the content of photosynthetic pigments in plant leaves, morphogenesis and phytochrome effects. (4).

In general, yellow light, with wavelengths of 447, 638, 669 and 731 nm, reduces the overall yield of tomatoes during germination. (4)

Orange light reduces tomato pigment, height, leaves number and photosynthetic pigment content in leaves and slows down their growth in the greenhouse (5). Orange light also reduces the content of chlorophyll in tomato leaves, and blue light can stimulate the formation of chlorophyll, and the length of tomato plant roots increases with blue light, but blue light significantly reduces the height of the plant (6).

Ultraviolet light with a wavelength of 380 nm stimulates the growth of tomatoes, and the plants have the largest leaf area and weight due to receiving this light. (7) The leaves of tomato plants grown under the influence of 380 nm light have the highest amount of pigment compared to other samples, but their growth slows down during the growing period in the greenhouse, So that these tomatoes remain unripe after eight weeks in the greenhouse. The amount of chlorophyll in the whole leaves of these tomatoes after two weeks of growth in the greenhouse is significantly lower compared to other samples.

Low light intensity by reducing the accumulation of lycopene leads to an inappropriate color of the fruit, but too strong direct radiation is also harmful for the fruits. (8)

 Lycopene synthesis is optimized when the green fruit is exposed to 650 nm light.

In 2009-2010, researchers at the Institute of Soil and Plant Sciences of the Agricultural University of Latvia have conducted experiments to investigate the effect of colored polyethylene plastic layers on the growth, yield and quality of tomatoes. They investigated the effect of the films on the plant in the wavelength of 400-700 nm (active photosynthetic radiation).

They planted tomato plants in special pots and placed them in high tunnels covered with plastic film in the greenhouse and used red, yellow and blue colored polyethylene plastic films to cover the greenhouses.

They also used a colorless polyethylene film as a control sample. In their experiments, the thickness of the films was considered to be 120 micrometers and they measured the light passing through the films at a wavelength of 400-700 nm (photosynthetically active radiation) with a spectrophotometer.

In this research, the length of the plant, the number of leaves and the content of leaf pigment during the growth of the plant were investigated, and the content of chlorophyll and carotenoid was determined by spectrophotometric method in the ethanolic extract of the plant leaves (9). They also measured the fresh and dry weight of tomato fruit and the content Lycopene was determined using spectrophotometric method after extracting ripe fruit samples with hexane.

They found that the color of the plastic film and the ratio between the red and blue spectrum changes during the growth period of the plant. Their experiments showed the effect of the color of the plastic film on the growth of the plant and the pigment content of the fruit.

Light transmission of polyethylene films

Transmission and reflection of light from polyethylene films depends on the color and freshness of the films. For new films, the highest amount of light transmission occurs for colorless film and the lowest amount of light transmission occurs for red film. The red film reduces the light transmission in the green-yellow region of visible light, the blue film also reduces the light in the red spectrum, and it is important that the minimum light transmission corresponds to the maximum absorption of chlorophyll.

The ratio of blue (400-500 nm) and red (600-700 nm) spectrum is important for the natural photomorphogenesis of different plants (10).

This difference in radiation energy can affect the growth and yield of tomatoes.

During the growth period of the tomato plant (110 days), the transparency and color of the plastic films and the ratio between the red and blue spectrum changes. The least color change occurs for yellow film and the most color change and loss occurs for red films. The ratio between red and blue spectra increases for blue and yellow films, decreases for red films and does not change significantly for colorless films.

Effect of plastic film color on tomato growth

The increase in plant length under the red film cover occurs more than other colored films, so that the growth of tomato plants under the red cover is 10% more than the colorless sample. But for blue films, decrease of 2-5% occurs in the length of the plant (11). researchers found that there was no significant difference in the number of tomato leaves as a result of the color of the polyethylene layer.

In another study, researchers proved that a significant increase in the chlorophyll content of plants occurs due to red and yellow plastic films in plant leaves at the beginning of the flowering stage. A process in which the color of the polyethylene layer causes carotenoid stimulation.

Brazaitit et al. (12) found that the accumulation of chlorophyll in tomato leaves increased due to the use of red and yellow plastic films, but decreased due to the use of blue films.

The effect of plastic film color on tomato yield and quality

A higher content of photosynthetic pigments generally indicates a faster photosynthesis process, which is related to a higher content of absorbing substances produced during the process.

Under the same conditions, the first tomato fruits ripen under the yellow and red polyethylene films, so that a significant increase in the tomato yield under the yellow plastic cover is observed, as well as a decrease in the tomato yield and the number of fruits under the blue polyethylene cover it happens (11)

The research results show a significant increase in lycopene in tomato fruits covered with yellow polyethylene, but for red and blue films, the lycopene content in ripe tomato fruits decreases compared to the colorless transparent sample.

  The process of increasing the length of tomato plant stems occurs when red polyethylene film is used, but the opposite is true for blue films.

Also, the research results indicate an increase in chlorophyll concentration in tomato leaves under red and yellow polyethylene films.

generally, it was determined by examining the results, blue polyethylene film is not suitable for tomato production, red films have disadvantages and advantages, but yellow polyethylene film is optimal for tomato production.