They imagine that cost-effective deep shafts for crop planting would be constructed using new drilling techniques. Existing coal mining and civil air defence tunnels, many of which are now abandoned could also be used for crop production. The new deep farms could be employed for intensive crop farming to feed rising urban populations.
The newly-patented concept for deep farms is an alternative approach to large scale crop production. The deep farms could be created close to, or beneath, population centres to reduce transportation costs and CO2 emissions.
Prof Riffat said: "A variety of crops could be grown in the deep farms using hydroponic planters - plant roots fed with nutrient-rich water - or aeroponics - growing plants in an air or mist environment. LED units would enable photosynthesis in the absence of sunlight. Groundwater could be used directly or water could be condensed from ambient air in hot/humid deserts. A major benefit of this approach is that crop production is largely unaffected by climatic or seasonal factors - one of the greatest limitations of conventional farming methods."
Prof Riffat says that many crops are now being grown in greenhouses and while this provides a controllable growth environment, greenhouses are heavy energy consumers. Vertical farms are a relatively recent adaptation of the traditional greenhouse and are suitable for use in cities, as their tall glass structures provide high crop yields on a small land area.
Prof Riffat added: "However, vertical farming systems are expensive to manufacture and install, and require a large amount of water and energy for heating and cooling. They are also vulnerable to extreme weather conditions, wars and terrorism.
"The new deep farms and also millions of redundant coal mines and tunnels in the world could be for crop production. In the UK, there are over 1,500 redundant coal mines, and in China, there are over 12,000 abandoned coal mines, 7.2 billion m3 of tunnels and about 1 billion m3 civic air defence tunnels."
Carbon dioxide is required for plant photosynthesis and the deep farms will use CO2 capture and release systems, as these spaces are well suited to carbon storage. Use of carbon capture systems has the added benefit of reducing CO2 concentration in the environment, as additional carbon is adsorbed in materials in the ground space. Advanced control systems including sensors and remote controls could be used to monitor crop production. Automated systems such as robots could be used for crop planting and harvesting. Electricity generated from renewable sources and off-peak power could be used to power the LED lighting for plant photosynthesis.
What are the problems with existing agricultural methods according to Professor's Riffat and Yuan?
- High dependence on natural resources, including water, arable land space, daylight, etc.
- Affected by irregular seasons and climates, industrial pollution, natural disasters, extreme weather, pests and diseases, man-made accidents and wars
- Inefficiency, including low production capacity, and inefficient use of natural resources
- Crops can take up harmful materials. Cultivated land and water are heavily polluted in many countries. For example, about one fifth of arable land in China is contaminated with levels of toxins greater than Government standards (2014 data), and 14% of domestic grain contains heavy metals such as lead, arsenic, and cadmium (2015).
Prof Riffat believes that many of these problems could be solved if agricultural plants were grown using deep farms. Deep Farms are not strongly affected by the seasons or climates, and are resistant to natural disasters, extreme weather, pests and diseases, man-made accidents and industrial pollution. In fact, the ground environment is naturally suited to the growth of plants.