Results temperature measurements Powerflex

FruitSecurity Holland cover at sweet cherries. Source: PCfruit - Proeftuin pit- en steenfruit.

Purpose

Verifying the value of the FruitSecurity Holland raincover in sweet cherries. In this trial, the construction and type of film of the FruitSecurity Holland rain cover is discussed. The influence on available light, temperature and humidity under the rain cover is also examined.

Trial Design

Since 2007, various covers have been tested on pcfruit. In recent years there have been a lot of evolutions as far as the construction is concerned. Therefore, the old sys-tems were replaced with the latest systems in 2016 and 2017. In addition, the covered area was further expanded.

Description of the rain cover FruitSecurity Powerflex (Netherlands):

• Material construction: concrete posts secured in the ground with steel bottom plates (anti-zinc plates) + steel posts reused from the Quick-Zip system. The end posts are thicker than the intermediate posts.
• Stabilization: the ground anchors (screw anchors) are attached with steel cables in one direction. On top of the post, the connection of the cables is done on post caps. In the row, the posts are connected once more with a steel cable.
• Ridge height: 4.0 m.
• Film: HD Polyethylene.
• Film attachment: Attached with adhesive strips. There are two strips of foil per row with an elastic connection to open and close. The foil overwinters on the ridge.
• Varieties: Regina and Karina on Gisela 5 and Gisela 3 and Poisdel on Gisela 5.
• The system is netted with an insect net against Drosophila suzukii (Ornata Air Plus - 0.77 x 1.02 mm).

Light dungeon

Every year a number of light measurements are carried out. For this purpose, the amount of PAR light is measured. The average light loss during these periods is shown in Table 1.

Table 1: Average light loss for each system over a longer measurement period.

Table 2: Difference in light loss between a sunny and a dark day.

Figures 1 and 2 show a comparison of available sunlight between the control and the Fruit Security rain cover during a high light and low light day.

Warming up under covers.

Temperature loggers were hung under the rain cover at 80 cm and 3-3.50 m heights. An effort was always made to hang the loggers in the crop. Temperatures are compared with measurements in an adjacent pear plot. For the calculation calculation, both day and night are included.
Table 3 shows the average temperature difference over the entire measuring period as well as the extreme peaks. The figures give an overview of both the temperature and the difference over a limited period.

Top crown irrigation FruitSecurity

Higher temperatures were often measured under the rain caps which could lead to poorer quality. During hot periods, an attempt was made to lower the temperature under the hoods by sprinkling over the sheeting with sprinklers/upper-crown irrigation. Sensors were suspended under the covers at heights of 1 and 4 m. In 2019, sprinkling was done for a short period of time (15 to 30 minutes), so the effect on temperature was very small.
In 2020, irrigation was carried out several times for 1 to 1.5 hours during the period between July 17 and 26, but no decrease in air temperature could be observed. The figure below (Figure 21) shows the temperature outside the cover and under the cover at a height of 1 and 4m. Sprinkling was carried out from 15h30 to 16h30 and from 17h50 to 19h10, but the sprinkling had no effect on the air temperature.
This may be a result of the low flow rate at the sprinklers. In 2021, if possible, the flow rate will be increased and the test will be repeated.

Conclusion

• FruitSecurity Holland has a relatively flat construction, which makes it easier to carry out work with tractor and sprayer and operations during picking.
• In 2016, the construction of the system took time, but the opening and closing of the cover is smooth.
• The light loss rate in 2020 was 39%, in 2019 no light metering was performed at this canopy, but in 2018 the light loss rate was 32%. In 2020, the difference in light loss between sunny (43 %) and cloudy days (28 %) increased compared to 2018.
• Since 2016, this system has been netted against Drosophila suzukii.
• In 2016, we felt in this cover that it was cooler on warm days. The measurements of 2017 and 2018 indeed indicated that downstairs the temperature is on average 0.5 °C lower. Especially in the morning, it is often cooler here. In 7 of the 17-day measurement period, a brief difference of 10 °C was measured between the cover and the control. The air under the cover warmed up more slowly. From noon onwards, the difference with the test plot without the cover was small.
• In previous years, the greatest difference (maximum 4 °C) in temperature was observed in the ridge around noon. At night it did cool down faster. Just before midnight, a lower temperature was measured under the rain cover. This period lasted 6 to 8 hours. On average, the temperature under the cover in the ridge was 0.8 °C higher.
• In 2020, it was noticed that, both at a height of 80cm and 3m, it was 2.5 to 3.0 °C warmer under the cover around noon. In the late afternoon and early evening, it was often slightly cooler under the canopy. In the morning, the air under the rain cover warmed up faster. Under the rain cover, it was on average 0.1 and 0.4 °C warmer at heights of 80 cm and 3 m, respectively.
• The relative humidity was almost always higher under this rain cap because of the control. Especially shortly before noon, at a height of 80 cm, there was regularly a peak of 25% difference. In the ridge, humidity was on average 4% higher under the canopy, but no extreme differences were observed here. The higher humidity provides a more pleasant climate, but can also lead to higher mold pressure or a more pleasant climate for pests.
• In 2019, a higher temperature was recorded under the cover during spring frosts. The average temperature difference was 1.6 °C (50 cm) and 1.1 °C (1.5 m). At both heights, it took longer under the cover for temperatures to fluctuate around freezing and positive tem-peratures were measured more quickly compared to the control plot. As a result, the frost period under the rain cover was shorter.

Decision

To limit the influence of light loss, it is always advisable not to leave the foil closed any longer than necessary. Therefore, the foil should be rolled up immediately after picking. Even in countries with more light than ours, this advice applies. Closing the film in poor weather conditions during flowering extends the period with less available light. Certain types of film cause major light losses from the start. Some seem to deteriorate faster in terms of light transmission. For the time being, there is no signal from abroad that flower bulb quality and yield would deteriorate in the long term.
In 2019 and 2020, closing the covers had a positive effect on temperature during the spring frost period. The average gain in temperature was 1.0 to 1.5 °C, depending on the type of cover and location, but it also requires time to close the covers and then open them after the frost period.