Professor Tony Trewavas: We need to return land to nature if we're to have a future

Meeting the needs of the present without compromising those of future generations is the basis of sustainability. Academic Hans Rosling predicts that by 2070 the human population will peak at about 11 billion, a 4bn increase from 2017. Arable agriculture occupies 10 per cent of the earth's surface and rough grazing another 20 per cent; no more useable land is obviously available. It is now commonplace to talk of the extinction of many obvious species of animals and plants, let alone those less obvious. Habitat loss is the primary cause and agriculture must share part of the blame. Eighty per cent of crop yield is currently fed to animals to satisfy our excessive desire (not need) for daily meat consumption. Current agriculture has increased efficiency some tenfold in the last century but nearly one billion people still have insufficient food for good health. In fisheries and the supply of water we still act like hunter gatherers fighting to maximise our supplies. Forests are still being cleared for crops or for the polluting foolishness of burning wood for energy. The goal must be to return huge swathes of land to nature, not only for the animal and plant life with whom we share the world but to ensure we do not damage the great cycles through the atmosphere and oceans on which our lives depend. We should aim to limit ourselves eventually to one half of the useable land and oceans and leave the rest entirely alone.

Professor Tony Trewavas FRS. FRSE

Making agriculture more land efficient is critical. Drones armed with sensors are overseeing an agricultural revolution. 30-40 per cent of crop yield is lost to pests worldwide. But daily inspection by drones targets pests before they are established. The reductions in pesticide use, are impressive with only 0.1 per cent of the pesticide needed compared to conventional spraying. Weeds are recognised and the growing point zapped with a laser obviating use of herbicides. Other sensors detect near infra-red emissions from crops.

Healthy vegetation reflects more infra-red light and weaker areas are identified using infra-red sensors and receive additional fertiliser. Walking robots assess soil structure variations providing the farmer with a choice of where and what to plant, leading to fields with mixtures of crops rather than the unnatural state of monocultures with its attendant pest problems. Sensors are also being used that detect size and colour of fruit, specifying ripeness of peaches, citrus fruits, bananas and apples. Growers are then alerted by smartphone to wheel out robots that recognise and collect the produce. At Harper-Adams University, scientists have begun a proof-of-concept experiment. One hectare of barley will be seeded, grown and harvested in which no humans enter the field from start to finish. Sensor collars are used to monitor cow and pig behaviour or inflamed udders to detect very early signs of illness, enabling rapid and early treatment.

To free much more land for nature requires a radical rethink. The tomato crop offers one direction. They are now grown hydroponically – nutrients flow past the roots and composition is computer controlled. Huge greenhouses are used with an optimised controlled environment, LED lights of known spectral efficiency to optimise photosynthesis and to maintain constant daylength, with pests controlled biologically by predators and extra CO2 provided from natural gas production. Current yield is 70 kilos/square metre, 15 fold higher than outside and needing only one tenth of the water. Double blind tests report that taste and quality are indistinguishable from field or organically-grown tomatoes, the variety being the biggest variable. Genes to improve flavour, lost in old-style plant breeding to increase yield, are now being returned. Robots armed with cameras assess ripeness and pick at the optimal time. Packaging is increasingly biodegradable and designed to maintain optimal freshness. Pilot studies show that excess heat absorbed by a greenhouse can be stored in large tanks of water underneath the glasshouse and be used to heat entire neighbourhoods in winter. Sustainability is gained by equalising inputs and outputs. Peppers, cucumbers, onions, leeks, carrots, parsnips, potatoes, aubergines and soft fruit like strawberries and cranberries are following this route.

Aeroponics, like hydroponics, rejects the use of soil altogether. An atomised fertiliser mist is instead applied directly to the roots and is specifically designed for the stage of growth. Aerofarms are located in very tall buildings. Multiple stacks of some 20 different leafy vegetables and herbs are grown under spectrally optimised LED light. 30,000 growth and environment factors are computer monitored and controlled. Estimated yields are near 70 fold higher compared to field grown; the crops use 95 per cent less water, 50 per cent less fertiliser and zero pesticides, herbicides and fungicides. Thirty annual harvests are cropped compared to three outside in a good year. These will help feed the mega-cities of the future.

Professor Tony Trewavas FRS. FRSE., Scientific Alliance Scotland