When most people picture British farming, they probably imagine fields of wheat,
potatoes or vegetables stretching across the countryside. But some of the food on supermarket shelves is produced in environments that look very different.
A tomato might spend its entire life inside a glasshouse, growing more than 20 metres tall with water and nutrients delivered directly to its roots. A lettuce could be grown inside a building, stacked on shelves under LED lights without ever seeing natural sunlight.
These systems – open fields, greenhouses and vertical farms – are sometimes presented as competing visions for the future of food. But they operate at completely different scales and, importantly, offer very different levels of control over the environment.
This matters as the climate changes. Moving crops indoors can protect them from
drought, heat and unpredictable weather. But that control comes at a cost.
The UK has around 17 million hectares of utilised agricultural land, with approximately 6.1 million hectares classified as croppable. Around 3 million hectares are used for cereals alone.
By comparison, the UK’s horticultural crops (ranging from tomatoes and peppers to cucumbers and strawberries) occupy only around 147,000 hectares, and glasshouses account for a small fraction of that (approximately 850 hectares).
Vertical farming is smaller still, and not separately recorded in national agricultural land-use statistics. I estimate that these farms only occupy 0.0001% of the UK’s total agricultural land (around 10-30 hectares).
Yet the amount of land occupied by a farming system does not necessarily reflect its importance to our food supply.
Fields provide scale, but are more vulnerable to the climate. If you eat a slice of bread, the wheat used to make it was almost certainly grown outdoors. The same applies to barley, oilseed rape, potatoes and many vegetables.
The great advantage of open-field agriculture is scale. Sunlight and rainfall provide two of the most important inputs for plant growth without farmers having to manufacture either of them. Growing millions of tonnes of wheat inside illuminated buildings would make little economic or environmental sense.
The trade-off is control. Farmers cannot decide when it rains or how hot a field
becomes. This becomes particularly important during drought. Irrigation can
compensate for a lack of rainfall, particularly for key crops such as potatoes and many other vegetables, but access to water differs considerably between farms.
A hosepipe ban does not automatically mean that farmers must stop irrigating. Domestic restrictions are different from the rules governing agricultural abstraction from rivers and groundwater.
But during prolonged drought, abstraction can also be restricted to protect water supplies and the environment. Agriculture therefore faces a difficult problem: crops often require the most irrigation precisely when water resources are under the greatest pressure.
Greenhouses offer control, but require a lot of resources. Walk from a field into a modern tomato greenhouse and the level of environmental control changes dramatically.
Plants may grow without soil while computers regulate irrigation, nutrients, ventilation, humidity and temperature. Modern systems can deliver water directly to the root zone and collect drainage water to be treated and reused. This means they can be up to 90% more efficient in using water.
Noi Pattanan/Shutterstock
That makes greenhouse production potentially very water-efficient. It also allows large quantities of crops such as tomatoes, cucumbers and peppers to be produced from a relatively small area. But water efficiency is not the same as water security.
The Netherlands, home to one of the world’s most advanced greenhouse industries,
illustrates this problem. Recent dry conditions have increased pressure on surface and groundwater supplies, affecting the availability of water for agriculture, including greenhouse horticulture.
A greenhouse can recycle water extremely efficiently, but it still needs an original source. Capturing rainfall from greenhouse roofs, increasing water storage and recycling irrigation water will therefore become increasingly important as drought risk increases.
Temperature creates another challenge. Greenhouses provide protection from the
outside environment, but they are not isolated from it. If tomatoes grow best within a particular temperature range, maintaining that range becomes harder as outdoor conditions become more extreme. When it becomes hotter outside, growers may need more ventilation, shading or cooling. During cold periods, additional heating is required.
This means that the way we operate greenhouses today may not be how we operate
them in the future. Climate change could require greater intervention simply to
maintain the same growing conditions. And intervention costs money.
Vertical farms sit at the other end of this spectrum of control. Crops such as lettuce, herbs and leafy vegetables can be grown on multiple stacked layers inside buildings – even several kilometres underground – with light, water, nutrients, humidity and temperature all tightly controlled.
Sergey_Bogomyako/Shutterstock
They can use remarkably little land and recycle much of their water. They are also largely protected from drought, storms and other extreme weather. But the greater the control, the greater the dependence on infrastructure and energy.
Even vertical farms are not completely independent of outdoor temperatures. LEDs and other equipment generate heat that needs to be removed. Maintaining an optimal indoor climate can require more energy as external temperatures move further away from the conditions required by the crop.
À lire aussi :
Four myths about vertical farming debunked by an expert
This exposes a fundamental trade-off in controlled-environment agriculture. The more we separate food production from the natural environment, the more energy and infrastructure we need to replace the services that nature previously provided for free.
The economics can become difficult. Vertical farming has demonstrated that crops can be produced using very little land and water, but the sector has also experienced numerous business failures. High energy requirements, substantial infrastructure costs and narrow profit margins have made it difficult for some technically impressive systems to become financially sustainable.
Resilience has a price
There is no simple answer to whether fields, greenhouses or vertical farms are the most resilient way to produce food.
Fields require comparatively little infrastructure but are highly exposed to weather. Greenhouses provide greater control but require investment, energy and secure water supplies. Vertical farms offer even more control, but with greater dependence on electricity and expensive infrastructure.
Climate change makes this trade-off increasingly important. The future will require smarter, rather than simply more controlled, agriculture: better water management in fields, greater rainwater capture and storage in greenhouses, more efficient heating and cooling, and increased use of renewable energy and waste heat from other industries.
We will need fields, greenhouses and vertical farms – for different crops in different places. The challenge is finding the right balance between exposure to a changing climate, and the increasing cost of controlling it.
You must be logged in to post a comment Login