FILFOR GREENHOUSE

The impact of light-converting film on the production environment and growth results of greenhouse strawberries

Light is the driving force behind plant photosynthesis, affecting crop yield and quality. In greenhouse production, the different light transmittance of light-transmitting films can alter the temperature and humidity of the greenhouse environment, indirectly affecting plant growth. Light-converting films are films with added light-converting agents, which can improve light transmittance and convert light wavelengths, transforming the weaker yellow-green light absorbed and utilized by plants into stronger blue-violet or red light, thereby improving light utilization efficiency.

In recent years, light-converting films have been increasingly used in the greenhouse production of fruits and vegetables such as tomatoes, cucumbers, watermelons, and melons. Related studies have shown that light-converting films can, to some extent, alter the greenhouse microenvironment, improving crop yield and quality. Studies on the effects of light-converting films on strawberry growth and quality are particularly relevant. This paper compares the differences in environmental conditions between light-converting film greenhouses and ordinary film greenhouses and their impact on strawberry growth and results, providing data reference for the selection of greenhouse films in greenhouse strawberry production.

Two types of greenhouse films were used in the experiment: a light-converting film and a regular film. The light-converting film was (Jigang brand light-converting PO film, Shandong Jigang Luna New Material Co., Ltd.); the regular film was (Xiangyanghua PO film, Xindian Xiangyanghua Plastic Factory, Linzi District). The thickness of both films was 0.1 mm. The experiment was conducted from October 2024 to April 2025. The experimental site was the strawberry planting base of Jinan Xiangquan Agricultural Technology Co., Ltd. The greenhouse was 92 m long, 12 m wide, 5.7 m high, and had an area of ​​1104 m2.

The experiment included two treatments: a greenhouse with a light-converting film and a greenhouse with a regular film, with one greenhouse per treatment and three replicates, for a total of six greenhouses. The strawberry variety was Zhangji (Sweet Treasure), and the planting date was August 20, 2024, using a double-row, raised-bed planting method. The greenhouse film was covered on October 15, 2024. The optimal temperature for strawberry growth is 18–25 ℃, with a lower limit of 9–12 ℃ for root water absorption and a higher limit of 28–30 ℃ for leaf growth. Measures were taken to cover the greenhouse with insulation blankets during nighttime low temperatures and open the ventilation openings during daytime high temperatures to keep the greenhouse temperature as close as possible to the optimal range for strawberry growth.

One Pengyun IoT S21A environmental data acquisition instrument was placed in the center of all the greenhouses. Air temperature and relative humidity sensors were positioned 20 cm above the strawberry plants, and soil temperature sensors were placed 15 cm below the ground surface. Data was automatically collected and recorded continuously. Data from December 15-24, 2024, and February 15-24, 2025, were collected to compare the heating rate and heat preservation and moisture retention effects of different film-covered greenhouses.

Three points were selected in each greenhouse (20 m from the center and 20 m from each side) to measure the plant and row spacing of strawberries, thus determining the number of plants per 666.7 m². The plant height, crown width, and leaf thickness of 20 strawberry plants were measured consecutively, and the number of flowers and fruits per plant was investigated. Fifty marketable fruits were randomly picked and their average weight was measured. Ten marketable fruits were selected and their soluble solids content was determined using an ATAGO PAL-1 saccharimeter. The yield per 666.7 m² was calculated using the formula: Yield per 666.7 m²/kg = Number of plants per 666.7 m² × Number of fruits per plant × Weight of fruit per plant (g) × Reduction coefficient / 1000. In this experiment, the reduction coefficient (marketable strawberry fruit rate) was 0.90, determined based on the ratio of the actual number of marketable fruits harvested in the field to the total number of fruits.

From December 15th to 24th, 2024, the average temperature of the light-converting film greenhouse from 5:00 PM to 9:00 AM the following day was 1.50 to 4.43 °C higher than that of the ordinary film greenhouse, indicating that the light-converting film had a better heat preservation effect than the ordinary film during this period. From 10:00 AM to 12:00 PM, the temperature rise rate of the light-converting film was faster than that of the ordinary film. From 2:00 PM to 4:00 PM, the temperature of the light-converting film greenhouse was slightly lower than that of the ordinary film greenhouse, indicating that the cooling effect of the light-converting film was faster than that of the ordinary film during the high-temperature period.

This indicates that the light-converting film, during periods of higher temperature, also slightly increases the relative humidity inside the greenhouse, which is suitable for strawberries' requirement of 50% to 60% air humidity.

The light-converting film showed a good warming effect on the soil temperature in the early stage (December), but the warming effect was not obvious in the later stage (spring), which was beneficial to the growth of strawberry roots.

The light-converting film has a peak light intensity at noon, with less scattering and refraction, which is beneficial for the coloring of white or pinkish-white strawberries, but the brightness of red strawberries is slightly worse.

The strawberry plants grown under the light-converting film greenhouse showed no significant difference in plant height, canopy width, and leaf thickness compared to those grown under ordinary film greenhouses. However, the average fruit weight was slightly lower, the soluble solids content increased by 1.92%, the taste was better, and the number of fruits per plant was higher. The yield per 666.7 m² was 5.75% higher than that under ordinary film greenhouses.

Compared to ordinary film greenhouses, the light-converting film greenhouse has better heat retention at lower temperatures and cools down faster at higher temperatures. As temperatures rise in spring, the heat retention effect of the light-converting film greenhouse decreases slightly, which is suitable for the temperature requirements of strawberry growth in spring. At higher temperatures, the relative humidity inside the light-converting film greenhouse is also slightly higher, with increased humidity during the day, suitable for the 50%–60% humidity requirement of strawberries. At lower temperatures, the light-converting film greenhouse maintains soil temperature well, and has little impact on soil temperature at higher temperatures.

The light-converting film effectively warms the soil temperature in the early stages, but its effect is less pronounced in the later stages (spring), which is beneficial for strawberry root growth. The light intensity under the light-converting film peaks at midday, with minimal scattering and refraction, which is beneficial for the coloring of white or pink strawberries. Red strawberries show slightly lower fruit brightness; the underlying mechanisms require further investigation. Strawberry plants under the light-converting film greenhouse show no significant differences in extension, plant height, and leaf thickness compared to those under ordinary film greenhouses. Soluble solids content is slightly higher, resulting in better taste. Individual fruit weight is slightly lower, but the number of fruits per plant is higher, leading to a yield per 666.7 m² that is 5.75% higher than that under ordinary film greenhouses. Therefore, the light-converting film can be widely used in strawberry production.