Techno plastics for the farmer of the future

In less than thirty years, there are likely to be 10 billion people on earth! That’s a lot of mouths to feed… And we already know that we’ll be hard-pressed for arable land, especially as global warming is likely to reduce the amount of it available. Though there’s no need to panic, there’s still an urgent need to find solutions. Some of the most promising include hydroponics, from the Greek word for “water” (hydro) and the Latin word for “put” (ponere). This technique consists of growing plants on a substrate made of sand, clay balls or rock wool, and until recently, it was mainly practised in greenhouses, particularly in the Netherlands.

A relatively new solution, hydroponic cultivation consists of growing plants in a substrate irrigated with a nutrient liquid that’s conveyed by a system of PVC pipes.

Plants grown this way don’t need to be in the ground, and the substrate they rest on is constantly irrigated by a stream of water enriched with mineral salts and various nutrients essential to their growth. These plants grow faster than their traditionally cultivated counterparts, and the greenhouse effect allows for several harvests per year. Plants are supplied with enriched water via a fairly complex irrigation system comprised of tubes and pipes. These are usually made of PVC, a chemically inactive polymer that’s very sturdy, if not virtually indestructible. Plus, it can be recycled fairly easily. As for the plants and the substrate, they’re placed in separate containers, most often made of polythene or even ABS — materials with the same properties as PVC.

Polymers: a breath of fresh air

Aeroponics is an even more innovative solution, and it’s been a growing success over the last twenty years. With this technique, plants aren’t grown in a substrate but in the air. Still in its infancy, this technique is the focus of much research by public and private organisations around the world. To grow plants in the air, their stems are suspended on small, flexible plastic supports so as not to hinder their growth, and their roots are enclosed in empty containers called grow chambers. These are also made of plastic, usually polypropylene. The suspended roots must be kept in the dark to avoid algae growth. The containers are usually black to prevent light from entering, and a nutrient solution is sprayed on the roots at regular intervals. Again, the system is complex and consists of pumps and a large network of PVC tubes with fine mesh grates at the ends to spray said nutrient solution. Aeroponics requires very little water as the droplets reach the roots directly without the risk of “feeding” weeds… An effective way to preserve this natural resource. Another advantage in regions with a temperate climate is that this type of cultivation doesn’t necessarily require heated greenhouses since the nutrient environment is controlled (concentration of nutrients, temperature, PH, etc.).

This all sounds great in terms of future-proofing agriculture, but these aren’t the only benefits associated with aeroponics. This is a “bare bones” type of cultivation that doesn’t require soil or substrate — all that’s needed to grow the plants is empty containers and an irrigation system. This means that only a small amount of polymers are needed in the manufacturing of such a system. This also makes it possible to potentially use the numerous flat roofs in urban areas to create new agricultural spaces without any major consolidation work. On a global scale, this represents thousands of hectares! This would encourage short supply chains, reduce the amount of CO2 in the atmosphere and be a profitable way of greening cities and improving their carbon balance.

With aeroponics, plants can grow in the air! Their roots are constantly sprayed with a nutrient solution. Without soil or substrate, it’s a “bare bones” type of agriculture, making it possible for a lot of farms to be built on the numerous terraced roofs in urban areas..

This reality isn’t as far off as you might think; some architects are now integrating areas dedicated to aeroponics into their urban building projects.

Plastics: the light at the end of the tunnel?

Our carbon footprint and its consequences are at the heart of many of this century’s challenges. Farming in heated greenhouses requires a lot of energy. Horticulturalists and other crop producers take this issue seriously, but they also know that without a heating system, it would be impossible (or at least much more difficult) for them to produce the crops the population needs to feed itself. Sure, in Northern Europe, we could manage without tomatoes in the winter, but the problem extends far beyond this simple solution. Thanks to greenhouse cultivation, we don’t have to import vegetables from warmer countries, meaning fewer trucks, fewer boats and therefore less CO2. However, in this energy-saving age, greenhouse cultivation is far from satisfactory.

Integrating flexible photovoltaic cells into polymer films would make it possible to supply agricultural greenhouses with energy. Many research centres are exploring this subject, and the first practical applications of this technology are expected to emerge before the end of the decade

The idea of integrating semi-transparent flexible polymer solar panels into greenhouse films is therefore gaining ground. Despite embedding photovoltaic cells into polythene films being far from a simple task, many research centres are looking into the subject, and projects are making progress. The solution is organic photovoltaic solar cells, a relatively new process (see https://plastics-themag.com/By-2030-we-hope-that-every-building-will-have-an-independent-source-of-green-electricity) which consists of printing and superimposing a carbon-based semiconductor material on a polymer film. Right now, their energy efficiency is lower than that of their silicon-based cousins, but organic solar cells are making headway. In addition, they should eventually be relatively inexpensive to manufacture. Their weight, flexibility and transparency are their main assets since these features allow the panels to take any shape and perfectly conform to a greenhouse’s curved structure. Their transparency offers another obvious benefit. Whether they will deliver sufficient power to heat greenhouses still remains to be seen… In the meantime, they will prove useful in aeroponic cultures since these don’t require heating. It only takes a small amount of energy to power the pumps within the irrigation system.

The Azmud project has been created to explore this idea further. This project involves eight partners from five different countries within the Mediterranean basin, and it’s funded by the European Union. Coordinated by the Spanish institution Aimplas, it seeks to improve the performance of greenhouses through innovative polymers. They have succeeded in developing a polypropylene film embedded with carbon-containing particles.

Once connected to an electrical source, this film heats up enough to warm hydroponic crops and help them grow. Admittedly, it requires an electrical input, but it’s still more sustainable than traditional greenhouse heating. In addition, this film has been developed to last 3 to 4 months before becoming biodegradable according to the standard required by the European Union for mulch films. Its opacity has also been adjusted to block UV rays, which are responsible for the spread of weeds. This doesn’t affect the cultivation of crops.

Farmers see agricultural plastics as a way to protect their land by eradicating the need for so many crop protection products. Collection systems have been set up in Europe to recover and recycle used agricultural films.

Reducing the carbon footprint, respecting biodiversity, improving water management and land quality… The future of agriculture is underway! Sustainable methods don’t necessarily mean that yields will be reduced. They may require drones capable of accurately mapping the fields and the nature of the terrain, as well as increasingly accurate satellite data to predict the weather, but this sustainability also depends on simpler solutions that rely on the efficiency and constant evolution of agricultural plastics and the willingness of farmers to implement good practices.