Impact of shading net on microclimate condition in orchards

doi:10.21203/rs.3.rs-1632752/v1

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Impact of shading net on microclimate condition in orchards

https://doi.org/10.21203/rs.3.rs-1632752/v1

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Due to various reasons such as climatic stresses, pest attacks, disease outbreaks, damage caused by insects and birds, etc., irreparable damages are done to fruit trees. One of the operational solutions in the world to reduce these injuries is the use of shading net in the gardens. In order to select the appropriate shading net, it is necessary to first determine the main factors required for plant growth and development so that the installed net does not have an adverse effect on them. In this research, changes in radiation, temperature, wind velocity, wind direction and relative humidity inside and outside of two shadehouse garden were monitored. Investigating of the graphs in temperature, relative humidity and light changing throughout the period indoor shadehouse gardens showed that the temperature inside the shading net was lower than outside but no significant differences were observed between the months. Regarding relative humidity and light, both parameters were more and less than outside, respectively, but no significant differences were observed between the months. In general, the study of changes in the mean of the three parameters of temperature, humidity and radiation in the whole period showed that the greatest effect of using shading nets on microclimate in gardens was on reducing the intensity of light received. Also when the wind velocity is high, the temperature inside and outside the shading net is closer to each other.

Shading net

temperature

relative humidity

wind and light

Iran, with 2.8 million hectares of orchards, is one of the countries with high potential in fruit production. Annually, for various reasons such as climate stress, pest infestation, disease outbreaks, damage caused by insects and birds, etc., product losses are caused and irreparable damage is done to fruit trees. One of the operational strategies in the world to reduce these injuries is the using of net coverings in the gardens.

In order to create optimal conditions in the controlled environments, it is necessary to measure and determine changes in climatic conditions, including temperature, humidity, light intensity and wind velocity. Based on this, it is possible to select the net with the appropriate mesh and color according to the need.

Light is one of the non-living factors of the ecosystem that plays an important role in food production. Many studies have been done on the effect of light and plant growth. Light is the most important factor in plant growth; the lack of light affects the external shape of the plant and its growth rate. A plant that grows in the dark usually has long, slender stems and the leaves do not spread. Both leaves and stems will be free of chlorophyll. If such a plant is exposed to light, the longitudinal growth of its stem will be reduced.

The effect of day and night or light period on the growth and formation of flowers or other phenomena is due to the existence of a property in the plant called photoperiodism. In plants, for example, flowering can be accelerated by changing the duration of light in the greenhouse and protected culture. This issue is very important in floriculture and gardening. In addition, the growth of seeds in some plants, the production of greens and the falling of leaves in autumn depend on changes in light radiation. Plants are divided into three classes in terms of sensitivity to light period:

Indifferent plants that are not sensitive to day and night to form flowers. Like some varieties of tomatoes and cloves.
Short-day plants that bloom on short days and if they are exposed to long daylight, their flowering will stop. Short-day plants grow vegetatively on long summer days and do not flower until autumn and winter, when the days get shorter like chrysanthemums.
Long day plants only flower in the long light period and if the light period is short, they only have vegetative growth. Such as marshmallow, spinach and iris.
The interval between the length of day suitable for vegetative growth and the length of day that produces flowers and seeds for a plant is called the critical period of light. Short-day plants flower on days shorter than the critical day length, and long-day plants flower on days longer than the critical day length.
Plants are also divided into three groups in terms of tolerance to light:
Sun-loving,
Shade-loving and
plants that need moderate light intensity.

Light usually has a direct effect on the intensity of transpiration. Usually during the day, the aerial openings of the leaves are open. This causes water vapor in the leaves to enter the atmosphere. At night, when the pores are closed, the amount of transpiration is greatly reduced.

The light waves that reach the earth from the sun have different wavelengths in which only waves between 380 nm (purple) and 760 nm (red) are visible and form the visible spectrum.

Natural light is important in terms of quantity, quality and duration of radiation. The quantity or intensity of light is the amount of light waves that reach the surface unit per unit time, and its unit of measurement is a candle or lux foot. In most parts of Iran, the light intensity is sufficient and sometimes several times higher than the plant needs. Qualitatively, different lights do different things in the plant; For example, a plant is not able to photosynthesize in green light, while red and blue light maximize photosynthesis, or blue-purple light is needed to produce red in apples or purple in eggplant.

The amount of light emitted to parts of the earth depends on the duration of the radiation and the angle of radiation. Due to the sphericity of the earth, sunlight shines at different angles at different times of the day. That is, it is projected vertically to the ground at the equator and completely diagonally at the poles. Therefore, sunlight travels more or less a distance in the atmosphere depending on its angle of radiation, and therefore the amount of energy received by the earth varies in different places and in different seasons. The duration of radiation has a direct effect on the growth and flowering of a large number of plants, which will be discussed in this section.

Temperature is one of the important factors in plant growth and development. Temperature, along with light, carbon dioxide, moisture, and nutrients, affect the growth and eventual production of crops.

All these factors must be balanced. Temperature affects the plant in the long run and in the short run. Plants are made up of different components that have different reactions to temperature.

The temperature of the fruit corresponds to the temperature of the air; as the temperature rises, so does the fruit, and vice versa. In contrast, the temperature of the flowers is higher than the temperature of the leaves or air, and the petals sweat compared to the leaves. The temperature of the plant at the top of the canopy will change more compared to the lowest part of the canopy. The upper bouts featured two cutaways, for easier access to the higher frets. The lower bouts featured two cutaways, for easier access to the higher levels.

The relative humidity of the environment depends on the temperature and wind speed. Higher temperatures usually lead to increased transpiration. When the air is not moving, the air around the leaves accumulates with water vapor, which reduces the evaporation process. If the air is saturated with water, a layer of water will form on the leaves and around them, which provides a good environment for pathogens that can attack the plant.

Every plant has the best growth in a specific temperature range, since plant growth is a direct result of the difference between the materials made in photosynthesis and the materials used in respiration, the appropriate temperature range of plant growth can be in the form of temperatures at which photosynthesis maximum and balanced breathing, defined. Plants that have a relatively high temperature range are called warm season crops (such as tomatoes, cucumbers, and peppers) and plants that have a lower temperature range are called cold season crops (e.g. Spinach and Cabbage varieties), therefore, the cold growing season in the northern hemisphere is spring and in the southern hemisphere is autumn.

In addition to the difference in temperature range of different plants, there are differences between different parts of a plant in terms of cold tolerance. For example, the wood of the apple tree can withstand cold up to -35 degrees Celsius, but its roots are destroyed at -10 degrees, or in the peach tree, the flower buds are destroyed by less cold than the leaf buds.

Some plant processes such as respiration, photosynthesis, fruit ripening and maturity are directly affected by temperature. In addition, flowering and fruiting of flowers are closely related to temperature. The minimum temperature for plant growth varies according to the type and stage of plant growth.

Most plants need a lower temperature at night and a higher temperature during the day for best growth, and uniform temperatures at night and during the day are not suitable for them. Also, their temperature needs are different in different seasons.

Anti insect screens and shading nets are widely used in agriculture. These nets have positive effects on product quality and quantity.

The application of these types of protections have reduced the intensity of radiation and wind velocity by 15 to 39 percent and 50 to 87 percent, respectively.

Increased in relative humidity from 2 to 22%, decreased in temperature by 2.3 to 2.5 degrees Celsius and decrease in evapotranspiration from 17.4 to 50% have been the effects of using shade net on orchards (Mahmood et al., 2018 and Ajmi et al., 2018).

The results of Mditshwa et al. research showed that depending on the type of nets, color and density of its texture, the relative humidity of the shading net increased by 3.2–12.9% and the radiation intensity, temperature and wind velocity were decresead 9–46%, 1.3–7.6% and 2.5–17.7% respectively. Decreased activity of bees and pollination under canopies is one of the issues that should be seriously considered.

The effect of shading net on morphology, growth and production of banana fruits in two fruiting periods in Jordan was investigated. In this regard, the plant was covered by black nets with different densities. The results indicated that the use of shading net was reduced photosynthesis by 30–80% compared to the conditions of non-shade garden.

Also, the weight of a cluster in the first stage of fruiting has decreased from 7–32% under the shading net condition. In the second stage of production, flowering was delayed for 6, 9 and 15 days and also the weight of the cluster is reduced by 8 to 55% (Israeli et al., 1995).

Climate changes and their impacts on citrus in South Africa is very worrying. One of these problems is the excessive increase of the maximum temperature and the decrease of the excessive minimum temperature, which reduces the size of the fruits and increases the water requirement. Also, the appearance of the fruit will be unfavorable due to wind, hail and sunburn. Covering trees with shading net is a method that increases crop quality and reduces water requirements, but reduces production (Stander and Cronje, 2016).

The effects of applying three types of shading nets (25% white shade, 50% and 75% black shade) on the growth and fertility of dragon fruit were investigated. All types of shading nets were reduced sunburn and enhanced color by reducing brightness and chromate content. Fruit length increased significantly but fruit width did not increase significantly in 50 and 75% coatings. Also, the skin and flesh of the fruits in these two types of coatings are red (Chang et al., 2016).

The use of shading net is an effective way to achieve a suitable environment for plant growth, production level and product quality. Combined application of shading net and cool air flow in areas with intense sunlight is able to maintain the ambient temperature by 5–10 degrees Celsius less than the outside temperature, increase the relative humidity by 15–20 percent and reduce the intensity of radiation by 30–50 percent.

The using of shading net in cold climate reduces heat loss and maintains the greenhouse temperature by 5 degrees Celsius more than the outside environment. This will reduce the energy required for heating by 15–20% (Ahmed et al., 2016).

Some nets are used to prevent pests, insects and other invertebrates from entering the garden environment. The shading net converts sunlight into specific wavelengths and provides the potential to influence plant morphology and physiology.

The effects of different lattice patterns and its color on light quality in product production have been investigated by Kotilainen et al. The measurements showed that there were large differences in both of sunlight reflection and the spectral ratio received in the shading net with different material, texture and appearance (Kotilainen et al., 2018).

The effects of shading net on quantitative and qualitative changes in radiation in avocado showed that the use of 20% shading net reduced photosynthetic active radiation by 25%, 36% and 9% in white, blue and red nets.

Research by Tinyane et al. in 2018 showed that blue and white shading net reduce temperature by about 26 percent and red canopies by about 7.4 percent. In their supplementary research, they reported that the color of the coating had a significant effect on the shading net temperature. The results of their research showed that the relative humidity was 2.9–3.24% higher than the open space. The environment under the white shading net had the highest relative humidity and the red shading net had the lowest relative humidity (Tinyane et al., 2018).

To measure the considered climatic parameters including temperature, humidity, wind velocity, wind direction and light intensity, a monitoring system was designed and built.

4 − 1 Climate Monitoring System

The climate monitoring systems in this project were designed and built to measure wind spees, wind direction, temperature, humidity and ambient light intensity. The components of these devices include a box containing electrical circuits, a metal base and arm on which wind speed and direction sensors are installed (Fig-1), Monitoring system online management page and Android system application that mentioned below.

4-1-1 Box

These devices consist of a box in which electrical circuits are placed to protect against environmental conditions. Various environmental parameters are measured by sensors and transmitted to the device. In order to be used in indoor gardens, the systems were designed to send the necessary information to the server using the SIM card installed on it. In order to facilitate the monitoring of the garden, in addition to the SMS sending system, the management page and the android application were also designed and operated for these systems.

4-1-2 Monitoring system online management page

As mentioned, in order to facilitate online monitoring of data, a management page and an application under android software were designed and built for the system. To increase the visual accuracy of the outputs in online monitoring, it was also possible to disable the charts as desired and investigate one or more charts.

4-1-3 Android system application

The application designed for these systems require android version 6 and above. After installing the application on the phone, the username and password specific to each garden would be entered by the administrator and the application be activated.

4-1-4 Dataloger hardware and sensors

Dataloger hardware structure of this system has a powerful processor and GPRS connection with the central server.

The light sensor measures the intensity of sunlight at a wavelength of 300 to 3000 nm.

Temperature and humidity sensors are able to measure and determine instantaneous changing in temperature and relative humidity of the ambient air with high accuracy and speed of response.

Wind velocity and direction sensors are also equipped with rotating wind cups with electronic counters for continuous calculation. Wind direction is measured using rotating plates.

Data collection was performed continuously and the data were transferred to the central server.

4 − 2 shading net introduction

In this project, according to the climatic conditions of the cities to create a controlled environment (climate fluctuations) and the type of live and non-living stress(s) in the areas, robust and inexpensive structural designs with the appropriate type of cover and were performed in the gardens. Also, the type of cover (mesh) selected depends on the type and intensity of environmental stress.

The components of the structure and cover of these gardens are:

Columns
Clamps
Steel cables
Inhibitory systems and foundations

The using of shading net will change the climatic conditions under cover. In this regard, according to the available data, changes in temperature, humidity and light intensity in the outdoor environment and under shading net in gardens to Natanz city (Isfahan province) and flower fields in Mahallat city (Markazi province) were monitored. Those cities were located in central of Iran.

Natanz is located in the north of Isfahan province, on the hillside of Karkas mountains range. This city height is about 1372 m above the sea level and it is close to the central desert of Iran. Natanz enjoys three types of climate as cold, warm, arid and moderate and this garden has cold climate.

Mahallat is located in central of Iran and has a cold climate, and strong winds during spring and summer. Mahalat was known as the city of flowers and plants. Mahalat is a city where so many greenhouses have been established and according to the provincial statistics, one percent of the area under cultivation of the cut-flowers and plants in the world has been devoted to Mahalat.

The temperature changing curves in the spring 2020 showed that during the night, the temperature inside and outside the shading net is almost the same temperature, but due to less light intensity during day, the temperature under the shading net is slightly cooler and at noon this difference in temperature inside and outside reaches its maximum. From noon to evening, this difference is again minimized so that at night, inside and outside of shading net are at the same temperature, but in general, the temperature difference is not significant (FIG-3 and FIG-4). This means that the presence of shading net was reduced the temperature range in which the plant is located by several degrees.

In the temperature changing curves during a day in summer, the synchronicity of temperature inside and outside the shading net is quite evident, but during the day when the sun is in the sky (10:00 AM to 06:00 PM), the temperature inside is slightly lower than the outside temperature and as the night approaches, the outside temperature of the shading net becomes cooler than the inside.

The relative humidity changing curves during a day in the spring shows that the relative humidity inside the shading net was higher, but this difference was not significant. As the diagram shows, with the beginning of the irrigation in the evening (from 16:00 to 17:30 when the irrigation operation was carried out), the relative humidity has increased (FIG-5 and FIG-6).

The relative humidity changing curves during a day in summer also shows that due to the cooler air inside the shading net during the day (10:00 to 18:00), the relative humidity is slightly higher. As night, the relative humidity outside the shading net increases (midnight to 6:00 AM).

The wind velocity changing curves on the temperature during a day in the spring also shows that at times when the wind velocity is high, the temperature inside and outside the shading net is closer to each other. These changing are most evident from 17:23 to 17:35.

The study of the effects of wind velocity curves on temperature changing in day and night in summer also shows that due to the temperature of the air in this month, unlike spring, the change in wind velocity did not have a significant effect on temperature changing inside the shading net.

Investigation of the curves of changing in the amount of light during a day in the summer shows that the use of shading net has reduced the intensity of radiation entering the garden. The peak of this decrease in light was from 12:15 PM to 02:30 PM, when the solar radiation was more intense.

Another interesting point is that the shading net acted as an optical filter that the less the intensity of the light outside the shading net, there was less changes inside the shading net.

In general, the results of this project showed that the use of shading net in the garden of Natanz in IRAN has reduced the temperature, increased relative humidity and reduced radiation received under the shading net. This result has been obtained by other researchers (Ahmed et al., 2016, Smit, 2007, Mahmood et al., 2018, Ajmi et al., 2018 and Mditshwa et al. 2019).

The graph of relative humidity changing throughout the period shows that the relative humidity outside the shading net has always been lower due to the warmer temperature in spring and summer but there was no significant difference between these differences in different months.

Investigation of changes in the amount of radiation received throughout the period also shows that the use of shading net has reduced the intensity of received radiation, but no significant difference was observed between different months.

The results of the whole period indicate that reducing of the intensity of light in the garden was the greatest effect of using shading net from May to August 2020.

Study of the monthly changing in temperature, relative humidity and light received throughout the period also showed that the temperature inside the shading net was lower than outside but no significant difference was observed between the months. Regarding relative humidity and light, both parameters were more and less than outside, respectively, but no significant difference was observed between the months.

The important point that was obtained in the study of the minimum temperature during the period is that the minimum temperature was recorded at about 5.7 degrees Celsius in the morning of 8 May 2021 at 6:04 AM, while the air inside the shading net at this time was 7.1 degrees Celsius. Temperature changing inside the shading net in the evening and early morning (2:34 AM to 7:34 AM) indicate that the shading net has caused the temperature under cover to be slightly higher than the temperature of field, which means that the shading net alone cannot prevent frostbite. Investigation of the maximum temperature also showed that at 13:58 on July 30, 2020, the temperature outside the shading net was 40.1 degrees Celsius, while the temperature inside the shading net at this moment was 37.8 degrees Celsius.

The results of this project showed that the use of shading net in the garden has good benefits in reducing the temperature, increasing relative humidity and reducing radiation under the shading net in spring and summer but cannot prevent early frostbite. Also when the wind velocity is high, the temperature inside and outside the shading net is closer to each other.

Acknowledgements

The author of the article appreciates of the Agricultural Research, Education and Extension Organization and Ministry of Jihad Agriculture in Iran that funded this research.

Funding declaration

The author declares that Agricultural Research, Education and Extension Organization and Ministry of Jihad Agriculture in Iran that funded this research by the project “Manufacturing companies of shading net and climate monitoring systems for greenhouses and protected cultures”, No: 9701-97035.

Declaration of interests

The author declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Competing interest reported. The author declares that Agricultural Research, Education and Extension Organization and Ministry of Jihad Agriculture in Iran that funded this research by the project “Manufacturing companies of shading net and climate monitoring systems for greenhouses and protected cultures”, No: 9701-97035. The author declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Impact of shading net on microclimate condition in orchards

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