Can we influence the solar radiation received by crops with the aim of improving their quality and yields?
The answer is yes.
Changes in spectral quality through coloured netting can act as a physiological tool to modify the crop microenvironment and promote plant growth and yield.
Climate change has a negative impact on the productivity and quality of fruit and vegetable production by influencing various biotic and abiotic factors.
Global warming effects are likely to increase the incidence of abiotic disturbances in plants. Therefore, active manipulation of the plant growth environment is commonly used to optimise plant yield and quality.
Understanding how plants respond to light allows us to act towards improving the yield and quality of crops:
- Maximum net CO2 assimilation of most C3 species becomes saturated at relatively low irradiance (600-900 μmol m-2 s-1), equivalent to 30-40 % of total sunlight on a typical seasonal growing day.
- Excess energy makes plants predisposed to photo inhibition, heat stress and stomatal closure, leading to a reduction in net photosynthesis, the process responsible for carbohydrate production.
- Sustained high temperatures (35-40 °C) can affect cell division, leaf expansion and reproductive development.
Light quality manipulation can be achieved in protected agriculture by means of photoselective netting, which promotes higher crop quality, composition and yields. In addition to these effects:
- It protects against adverse environmental conditions: excessive solar radiation, heat, drought, wind and hail.
- It protects against flying pests.
- It reduces post-harvest losses and water consumption.
How can we manipulate the radiation reaching the crops?
Based on yarn pigmentation and weave design with different fibres and densities to create specific shade indices, photoselective coloured shading netting provide various mixtures of unmodified and scattered daylight with spectral modification.
Light passing through the holes in the netting remains unchanged in quality, while the light incident on the yarns is spectrally modified and scattered as it exits. Light scattering can be increased by 50 % or more.
Spectral manipulation intends to specifically promote photomorphogenetic/physiological responses, while light scattering enhances the penetration of light into the inner canopy.
These may be used to change the ratios of red to far-red light detected by phytochromes, the amounts of radiation available to activate blue/ultraviolet-A photoreceptors, blue light involved in phototropic responses mediated by phototropins, and radiation at other wavelengths that may have an influence on plant growth and development.
What is the difference between black netting and coloured netting?
Black netting simply reduces the intensity of light, without affecting its quality.
How do colours impact on the different photomorphogenic aspects of the plant?
- Pearl colour has the highest light scattering capacity in the visible range and also absorbs light in the ultraviolet range (UVA+B), therefore it has been proven that it increases fruit size and yield in tree fruit crops, as well as the post-harvest quality of fresh fruit.
- Red and yellow colours specifically stimulate vegetative growth rate and foliage vigour (plant height, width and number of branches).
- Blue colour causes dwarfing, reduced branching and leaf size.
- Grey colour improves branching and leafiness, together with reduced leaf size and variegation due to its clear absorption in the IR range.
The effect of colours varies from crop to crop; species respond to them differently.
Red, pearl and yellow netting significantly increase yields, improve fruit quality, reduce pest and disease infestation and improve post-harvest life.
Shading increases leaf area index (determinant of net/photosynthetic assimilation rates and yield).
