The Greenhouse Effect - Environmental Issues

Is it sustainable, people ask, to grow tomatoes in glasshouses in northern Europe, using precious fossil fuel to heat them, when they can be grown in the sunshine of southern Europe and imported here?

An apparently simple question, but with a rather more complicated answer. British tomato growers can claim outstanding achievements in environmental protection. These achievements are based on:

  • A substantial reduction in energy use for heating glasshouses.

  • The almost complete elimination of pesticide use.

  • Major reductions in the use of fertilisers and their loss into the environment.

  • Highly efficient use of water, an increasingly scarce resource.

  • Substitution for imports with their associated "food miles" and lower environmental production standards.

People in glasshouses

Almost all tomatoes in Britain are grown in glasshouses. The major components of glasshouses are glass and aluminium, both very durable materials. If properly maintained, glasshouses will last for 50 years or more.

Most of our imported tomatoes come from Spain and the Canary Islands, traditionally through the winter, but with the season being increasingly extended through the rest of the year. The adoption of long-life varieties, to withstand the transport involved, has played a major part in this development.

Even in Spain, the sun does not always shine and most crops are now grown in greenhouses covered with polythene. The polythene has to be replaced every three years or so and it can take up to five times the area of polythene greenhouses to produce the same quantity of tomatoes as in British glasshouses in a year. This means that in the 25 year life of a glasshouse (some are still being used after 50 years!) it could take 40 times the area of polythene to produce the same weight of tomatoes. What is polythene made from and what happens to it after use?

The same sort of factors apply to the use of water.

Many tomato crops in southern Europe are now commonly infected by diseases, such as Tomato Yellow Leaf Curl virus (TYLC) and Pepino Mosaic virus. TYLC is transmitted, mosquito like, by the tobacco whitefly (Bemisia tabaci) moving from plant to plant when feeding.

The tobacco whitefly has become a serious problem because there is a much greater reliance on pesticides in southern Europe than in Britain. It has become resistant to many of these pesticides, which no longer give good control as a result. So far we have managed to keep Bemisia out of the UK and do not have its associated virus to contend with. We have also taken much more stringent precautions against viruses and viroids such as Pepino Mosaic virus (PepMV) and Columnea latent viroid (CLVd) than in other European countries.

Recently another potentially serious pest, the South American tomato moth (Tuta absoluta) has arrived here in fruit imported from Spain. British growers, working with some of the world’s best entomologists, are continuing to develop control strategies for this and other potential new pests.

Energy Use

Since 1990 British growers have reduced annual energy use by more than half 50% for each kilo of tomatoes of the same type and quality produced.

During this period the majority of the production area was converted to use natural gas for glasshouse heating, resulting in less of the sulphur emissions which would come from burning oil or coal. Carbon dioxide can also be extracted from the clean exhaust gases when burning gas, to enrich the glasshouse atmosphere with CO2. This gives big production and quality benefits as well as further reducing atmospheric CO2 emissions.

Combined Heat and Power (CHP)

Combined Heat and Power (CHP) is one of the most exciting technical opportunities for the UK tomato industry. It involves the siting of electricity generating stations on tomato nurseries. These systems are fuelled by natural gas and produce electricity, which is then supplied to local homes, hospitals and businesses through the national grid. The heat which is generated is then used to heat the glasshouses, rather than being wasted through the cooling towers needed at conventional power stations. Electricity is generated at around 80% efficiency compared with the 30% in those conventional power stations, which would otherwise produce this power. These systems are also now being fuelled by biogas produced by digesting vegetable waste, crop residues or using crops grown specifically for this purpose.

Tomato crops are also being heated by surplus energy from industrial processes, which would otherwise be wasted. CO2 generated from these processes, is also used to supplement the glasshouse atmosphere to stimulate growth and production and reduce the loss of this CO2 to the environment. One example of this sort of opportunity is the development of glasshouse tomato production alongside British Sugar’s refinery in Norfolk.

The UK government is committed to stimulating CHP development as one of the largest potential contributors to reduced greenhouse gas emissions and environmental protection.

We estimate that over half of the UK tomato production area is now equipped with CHP facilities. This figure could rise further but one current problem is in the imbalance between the high costs of gas or oil and the price of electricity.

Some growers are using renewable energy sources to heat their greenhouses e.g. straw or wood chip.

CO2 uptake by British tomato crops is estimated to be 20-25,000 tonnes per year. This means that British tomato growers have reduced CO2 emissions massively in the past 15 years. How many other industries could claim anything like this?

Pest and Disease Control

Food safety and environmental sustainability are absolute priorities for British growers. They pioneered the use of natural means of pest control to avoidthe use of pesticides. They also all use bumblebees for pollination.

British tomato growers were the first to use natural enemies of pests, rather than chemical sprays, as a way to control them. These natural enemies are raised and supplied to growers by specialist biological control companies.

Each pest has its own predator or parasite, sometimes more than one,  growers have become highly skilled at monitoring their crops detecting pest attack at an early stage. They also have to maintain a balance between the natural enemies introduced to the crop and the pests. A true glasshouse ecosystem.

This simple system is very effective. Pests have become resistant to many insecticides. This means they no longer work. Another bonus is that glasshouse workers no longer come into contact with chemical pesticides and neither do the two million bumblebees which are used by all British tomato growers to pollinate their crops. Bees don't like pesticides either!

The other reason British tomato growers can make this approach work is that they have sophisticated glasshouses in which the environment can be precisely controlled. This also reduces the risk of tomato plants becoming diseased. For example, potato blight can be a serious problem, especially during wet summers. It does not affect commercial British tomato crops simply because growers are able to keep their plants dry. This is not possible with outdoor crops or those grown under plastic in southern Europe.

Tomato growers were among the first to develop Integrated Crop Management (ICM) production protocols with their customers. These became the NFU/Retailer ICM protocols, now the ’Red Tractor Farm Assurance’ (RTFA) Protocols. Glasshouse tomato growers currently represent a higher level of registration and compliance with the RTFA scheme than those of any other crop. A little red tractor on food packs means they have been produced according to this scheme.

Few, if any, pesticides are used on British tomato crops and the TGA objective is to eliminate all such use. Some growers have already achieved this. Where pesticides are necessary then those used in organic production systems (biological agents, sulphur, starch and soap sprays) are the preferred options.

British tomato growers have eliminated the use of peat for growing their crops, most now being grown in rockwool or coir as well as Nutrient Film Technique which uses no substrate at all! or. Organic crops are still grown in the soil.

Fertilisers and Water

Grower-funded research has resulted in substantial reductions in nitrate applied to UK tomato crops (up to 50%) and even larger reductions in nitrate emissions to the environment, such as in watercourses. Phosphate application rates have been reduced to a similar degree over the past 10 years.

Nutrient and water recirculation systems, such as the nutrient film technique (NFT), were developed in the UK. NFT is used by a number of tomato growers and this eliminates all nutrient loss to the environment, except that from final plant decomposition. The plant roots are bathed in water and nutrients, which then drain into tanks before being checked, adjusted and reused. Glasshouses now being built for tomato production have the facility for water and nutrient recirculation.

Tomato growers are developing systems for composting of plant waste (removed leaves during the season and plants at the end of the season) or utilising in bio-digestion systems thus dealing with waste in a sustainable and environmentally friendly way.

Import Substitution

Few, if any, British tomato growers are more than 100 km from a supermarket distribution centre or wholesale market.

Around three-quarters of current UK tomato consumption is of imported fruit. Most are from Holland, Southern Spain, the Canary Islands and North Africa. Delivery to British supermarket shelves requires lengthy transport by road or sea. As a consequence, imported fruit can be well over 7 days old before it arrives on supermarket shelves! British tomatoes can be picked today and in stores within 24 hours!

The British Tomato Growers’ Association believes that further developing and promoting British production will benefit the environment with the consequential reduction in food miles relative to imported tomatoes.

Locally and sustainably produced and locally consumed is great for the environment and great for the consumer too who can enjoy a fresher, tastier British tomato! 

Fact 06

Did You Know?

Approximately 2,500 skilled people are currently employed in the British tomato industry.

Roly Holt

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Roly Holt

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