French & Spanish Tunnels

French tunnels heralded the extension to both ends of the strawberry growing season about 15 years ago. In the last 5 years we have seen multi-bay Spanish tunnels emerge to revolutionise crop production and marketing, and prompt the development of completely new production systems for UK growers.

Field (GB) Ltd pioneered the original development of 'bespoke' French tunnels in the South East, and was quick to spot the potential of the Spanish design along with a number of enthusiasts. Major marketing groups, led by forward thinking growers, quickly addressed the need to strengthen tunnel structure to contend with the UK's fickle climate. Interest in 'tunnelling' was greatly assisted by EU Producer Organisation funds to promote the concept of market development from protected crops.

The rapid rise up the learning curve, and the enthusiasm to address the challenges of tunnel production came on the back of success, with reliable crops grown out of the summer rains, with consistent and extended cropping keeping the shelves of multiple retailers filled with home-grown supplies.

"The whole experience has been one of the right product being available to growers in the right place at the right time, at an affordable price commensurate with returns," said Roger Moore, General Manager of Field (GB) Ltd.

He estimates that following 5 years of development some growers have in excess of 50% of their production capability under cover, with possibly on average about 33%+ of the total UK area now covered. The use of tunnels has had a rapid take-off, which has now slowed up, even though new 'tunnellers' are emerging every season.

"For some, tunnel investment continues to rise, as they see the benefits to their overall business. For others, it is an adjustment relating to investment opportunity and individual ability," observed Roger. "The whole attitude of the industry is one of evaluating cost benefits, and adjusting business strategy to meet the needs of their customers".

Whilst the multi-bay Spanish tunnel has seen steady improvements to its design, especially around the tunnel ends, such changes have not been revolutionary, merely evolutionary. Larger diameter steel (from 35mm to 40mm) has been used as tunnel width was increased, additional wires, bracing and drop tubes have been introduced to give additional strength and resistance to winds. Open-ends have replaced 'bell-ends' for ease of access and more versatile ventilation practices.

"All this has been achieved by listening closely to our customers as they met the challengers of the new growing environment," added Roger Moore. "At the same time their enthusiasm to embrace new concepts and growing methods accelerated the introduction of substrate bags and pots, watering and feeding systems. The combination of all these disciplines represents one of the most dynamic changes in a sector of the horticultural industry ever witnessed. I would guess that there are probably up to 1000 hectares of tunnelled crops in the UK".

It was quickly recognised that these new practices brought new challenges that had to be met. 'Attention to detail' became the by-words - skills in tunnel site selection, construction methods, skinning practices and roping techniques were all rapidly perfected. The ability to increase temperatures in the early spring, and the ability to keep tunnels cool when fruit was ripening were central to successful crop management.

One of several technical developments has been the emergence of specialist covering films (skins) to challenge the standard clear UVI plastic film. Various grades and qualities have been tried to extend the life of the cover, and films with various colours have been investigated to reduce disease incidence. Field (GB) Ltd has introduced their 'Luminance' film, manufactured by Visqueen, which has positive 'thermic' properties.

"Luminance scatters the light molecules through the film, giving it a strange translucence," said Roger Moore. "Although there is a small reduction in light available to the crop, its main cost effectiveness is derived from its ability to raise tunnel temperatures in the early spring by a degree or two, and equally importantly to cool the tunnel environment by a similar amount later in the season, combined with more even growth".

"By working closely with our customers we have developed this film, which, to date, is giving positive cost benefits to growers".

A major trend for tunnel growers is a heightened awareness of the need to monitor the growing environment for temperature and water requirements. Whether substrate or soil, the water and nutrient levels are closely monitored as would a field grown crop by analysis and probe. Field (GB) has developed the Irrigard T sensor unit for monitoring the temperatures within the tunnel environment.
"One of the keys to quality fruit with maximum shelf-life is the growing environment", explained Roger. "Tunnels create Mediterranean climates at times, not ideally suited to our varieties. Irrigard T is a sensor package that enables the grower to set parameters of temperature related to the stage of development of the crop which notifies him/her when the tunnel temperature is outside these parameters".

Currently growers are seeking ways and means of keeping tunnels cool at such times, whether removing the ends, lifting up the sides, or pulling shade netting over the tunnel. Growers using table-top systems have the greatest challenge as the crop is higher off the ground and hotter by several degrees. "Some growers have tried external sprinkler-misting units to keep the tunnel surface cool," said Roger Moore. "This plus Luminance is helping in a positive way".

They have also contributed to the development of improved substrate bags by working closely with their growers; and by recognising use of peat as a base product for the bag, have developed new ideas with their customers. "UK growers like to double crop their bags, which, in a few cases has led to problems of when over-wintering," explained Roger. "By introducing Perlite into the formulation we have created a free-draining, warmer, lighter bag to improve the plants. Coir and bark have been introduced to reduce dependence on peat".

"Parallel to this is the range of plant containers, from an orthodox range of substrate bags of varying sizes and volumes, trough and winged growing systems, pipe and pot culture, and hanging pots, tubs or channels. This represents an enormous range of levels of investment to suit a range of pockets and reflect a range of expertise available within the industry".

Roger Moore is convinced that the greater degree of precision in growing high yields of high quality will come from environmental data generated by loggers and the grower's ability to respond with appropriate action. "Better tunnels, better substrates and closer attention to a detailed growing environment will give good paybacks," said Roger. "Add this to better plant material and better varieties and one can see the continued development of crops under tunnels as performance moves forward".

Reproduced with kind permission from The 2002 Strawberry Handbook published by A.C.T. Publishing www.actpub.co.uk

Clovis Lande Associates Ltd
Branbridges Road, East Peckham, TONBRIDGE Kent TN12 5HH
Tel:01622 873900 Fax:01622 873903
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