Shade Screen and Citriculture

Abstract

Sustain citriculture faces various environmental challenges like rising temperature, increase solar radiation, and warm nights during flower bud induction, particularly in arid and semi-arid regions. Shading net represents an intermediate solution to maintain the growth and productivity of citrus trees under fluctuation in climate conditions. Shading techniques protect plants from different biotic and abiotic stresses, by modifying the microclimate around the trees. Numerous benefits of shading net include reducing leaves temperature and decreasing light intensity, particularly at midday in the summer season, improving tree vigor, reduce physiological disorder and enhancing fruit quality.

Keywords: Arid regions; Citrus; Fruit quality; Rising temperature; Shading net

Background

There are negative impacts of abiotic stress on citrus trees due to fluctuation in environmental conditions, particularly increasing solar radiation, rising temperature, and warm nights. Usually, citrus trees are grown in the open fields under full sunlight conditions. While rising temperature and increasing solar radiation particularly in arid and semi-arid, represent more challenges facing citrus growers due to their different negative impacts on citrus growth and productivity [14].

There are various environmental factors threatening citriculture and affecting the sustainability of citrus orchards, that include higher temperature, excessive solar radiation, reduced rainfall, raised carbon dioxide (CO₂) levels,…etc. Currently, there is more interest in using shade screens in citrus orchards, particularly, in the arid and semiarid regions such as the Mediterranean area to protect the trees and improve fruit quality [11].

There are negative influences of excess solar radiation and rising temperatures on trees, such as increased water transpiration, and diminished light-use efficiency, which causes a reduction in CO₂ assimilation, tree vigor, and crops [7]. Therefore, protecting fruit orchards from the fluctuation of climate conditions is considered a serious challenge for fruit producers worldwide. Shading net is considered a novel technique to reduce the negative impacts of excessive environmental conditions in fruit orchards and enhancement microclimate around the trees. It could use in different ways, closed shading, partial shading, and periodically shading during hot summer [13].

Temperature Requirement for Citrus

Citrus as a subtropical crop needs moderate temperature above 12.8°C and not exceeding 35°C to grow and produce economic yield. Citrus could grow in different climatic regions except for frozen ones. Currently, both the Mediterranean climate and region are considered the most suitable for achieving the best growth and productivity of citrus.

Currently, the main cultivation area for Citrus is in warm regions from tropical to arid regions. It could grow in varied temperatures from 10°C to 35°C, while flushes start at 12.8°C and accelerate growth up to 35°C, while, rising temperature more than 35°C inhibit growth until stopped at 45°C, furthermore, the excessive temperature of about 50°C kill new shoots and small fruits [1].

Some Environmental Challenges for Citrus Growers

Under field conditions, citrus trees are subjected to various abiotic stresses that have negative impacts on the vegetative growth, yield, and fruit characteristics of different fruit orchards in different climatic regions.

The main environmental factor that inhibits the growth and productivity of citrus are considered as follow:

Rising Temperature

Continuous increase of temperature particularly in extremely hot summer has harmful effects on various crops. In citrus orchards, increased air temperature than 35°C inhibits growth and demolishes chlorophyll, increases fruit abscission, produces poor fruits, and reduces yield [1,6].

Warm Nights during winter and spring

The chilling requirements of citrus are very low compared to deciduous trees, with flower induction occurring during winter after meeting their chilling requirements during the period (from mid- December to mid-January) approximately.

Warm nights as a symptom of climate change during winter affect negatively on flower induction and fluctuate flowering and fruit set which could reduce tree yield [10].

There are various negative impacts of warm nights particularly during winter on citrus trees as follows:

- Constrain flower induction

- Decrease flowering buds.

- Delay bud-break.

- Alter the flowering stage.

Excessive Soil Radiation

Due to fluctuation in climate conditions, there is an increase in solar radiation, which increase evapotranspiration and affect negatively tree vigor (Figure 1), which increase physiological disorder such as fruit sunburn, particularly in some mandarin cultivars, and increase fruit cracking, which affects negatively fruit quality [8].

    

    

    Figure 1: Field image of Lemon trees in South Egypt desert [1].