Using photo selective films to enhance the profitability of leafy salad production in Wales

The wide uptake of polytunnels in the horticulture sector has offered growers a range of benefits of production such as an extended growing season, improved environmental management, enhanced resource use (e.g. irrigation) and improved efficacy of biological control compared with open field production.

Initial development of polytunnel films focused on high transmission of sunlight and extending durability. More recent development has led to a range of new photoselective polytunnel films which are able to modify the light that passes through a polytunnel to control certain growth characteristics and reduce diseases:

• UV transmission – Improved UV transmission can impact pest/disease development, and can improve the colour and nutritional value of crops (e.g. anti-oxidant content).
• Diffuse Transmission – Incoming light is subject to a high degree of scattering, creating a haze of light. Increasing light scattering improves distribution of light within the canopy, and can improve overall growth rates.
• Red: Far Red Modification – The ratio of red to far red wavelengths is an important physiological signal that can impact plant habit and the ratio of biomass invested in leaf and stem sections.

There is limited uptake to photoselective films within the small scale grower community which can be explained by the lack of knowledge about them, however they could have great potential. In this project two small scale horticulture units in Anglesey and Flintshire will trial three different photoselective films (Sunmaster Diffuse, Sunsmart Blue and Sunmaster Crystaltherm) alongside a conventional UV-stabilised polythene film (for comparison) over two growing seasons.

The project plan:

The crops that will be included in the trial on each site will include a minimum of three contrasting cultivars (e.g. closed/open head lettuce, lollo rosso, green and pigmented mizuna, baby leaf and rocket).

Various individual tunnels of 1m x 4.8m will be covered with different films and laid out in a randomised block pattern which will cover an area of 5 x 14 m on each site. A combination of cultivars will be grown in each tunnel.

The growers will receive support by expert consultants on disease control and also training on plastic handling and tunnel construction methods to maximise their longevity. The crop performance will be monitored throughout the growing season along with pest and disease incidence. On harvest the following information will be collected:

• Time from sowing until harvest
• Fresh biomass (individual plants and of gross harvests) and marketable yield. Cultivars will be selected on the basis of similar specifications to allow comparable planting densities, growth periods etc. to be achieved. 
• Crop colour (e.g. chlorophyll, anthocyanin content)
• Leaf area, number and head architecture 
• Postharvest life span – leaf failure over a given storage period matching usual commercial practice.

The project will provide information to other growers who are interested in photoselective films on whether there are significant benefits in terms of nutritional and visual characteristics of plants grown under these films. It can also potentially provide guidance on which type of film is best suited to their site conditions or crop type. Hopefully the films can provide a relatively low cost solution to increase productivity on small scale horticulture units.