Hydroponics, a crop technique allied to sustainability (2024)

Hydroponic crops save water, land and resources, and are key to sustainable agriculture.

Environmental conservation is one of the great challenges facing society and some of the current forms of agriculture pose a threat. In fact, the United Nations Food and Agriculture Organisation (FAO) presents it, along with other sectors, as one of the most common anthropogenic causes of soil pollution. Deforestation, caused largely by soil conservation for agricultural use, and the greenhouse effect emissions produced by the farms themselves bring the sustainability of the current model into question. However, there are alternatives such as hydroponics, a more sustainable form of cultivation that can be used in urban environments in order to be closer to consumers.

What is hydroponics

Hydroponics is a crop system that makes plants grow in a nutrient-rich water solution; in other words it does not use soil. Furthermore, the water used can be recovered and recycled, and the nutrients can be obtained from a variety of sources, including fish excrement (a technique known as aquaponics).

Growing plants in water without the need for soil is not new. The first mentions appear in a work by Francis Bacon published after his death (1627), Sylva Sylvarium. At the end of the 19th century, two German botanists (Julius von Sachs and Wilhelm Knop) described the list of elements that the solution had to contain to nourish the plants. Since then, it has been a form of cultivation commonly used in laboratories, but which in recent years has become important as a way to produce food with a higher yield and less use of land, water and energy.

Hydroponics and sustainable agriculture

Hydroponics is put forward as a solution to combat climate change, to reduce the environmental damage and species extinction caused by overexploitation and intensive farming. It also allows for a more rational use of water, an ever-scarcer resource. Hydroponic crops are also more profitable and easier to control, which turns them into a weapon to fight against hunger and to enhance food safety, especially in developing countries. According to the consultancy Berkshire Hathaway, the global hydroponics market is expected to grow to US$725 million by 2023, with a compound annual growth rate of 18.1 %.

Hydroponics is also one of the latest trends in smart farming, which consists of using technological tools, from geolocation to big data, artificial intelligence, the Internet of Things and drones to achieve greater yield from crops. The first vertical hydroponic farms, veritable skyscrapers dedicated to growing plants, are already being built in Droten (Holland), a country where soil and sun are scarce.

Characteristics of hydroponics (materials)

Traditional agriculture could be said to be an art, but hydroponics is a science in which all the elements that determine plant growth are controlled. We explain below:

Nutrient solution

The composition of the nutrient solution requires sufficient concentrations of nitrogen, potassium, phosphorus, calcium, magnesium and sulphur, as well as other elements in smaller quantities. Many are obtained from salts, but they can also be supplemented or even substituted by organic fertilisers, such as cattle manure or bird guano. Other possible sources of nutrients are organic compounds such as fish-meal, wood or grain scraps, or seaweed.

Substrates

In hydroponic crops, the plants draw the nutrients from the solution, but they still need a support and the roots have to be sufficiently aerated. Some of the most widely-used substrates are:

• Perlite, pumice or vermiculite: very light and porous stones that retain water but allow air to circulate through the roots.
• Rice husk, wood fibre or wool: these break down slowly, but they are very efficient in keeping the roots aerated.
• Rock wool: this is obtained by melting basalt rock and obtaining filaments that form a kind of sponge that does not break down.

Hydroponic technology

A hydroponic crop requires more technology and precision than a conventional one. Some of the necessary instruments and equipment are:

• Conductivity meters: the electrical conductivity of the nutrient solution indicates the amount of dissolved nutrients and whether they need to be replenished.
• pH meters: it is essential to control the acidity of the solution and substrate, as the optimal level is different for each crop.
• Lighting: Sunlight, artificial light, or a combination of both can be used to maximise yield. In recent years the use of LED lights has increased due to their low consumption.
• Air control: in closed environments, the concentration of CO₂ in the air can be increased to improve fertility.

Hydropronic crops and plant types

Almost any plant can be grown with hydroponics, but certain hydroponic plants work particularly well:

Greens: green beans, cauliflower, cabbage, celery, broccoli, lettuce, pea, leek, spinach.

Vegetables: carrot, beetroot, cucumber, aubergine, onion, pepper, radish, courgette, tomato.

Fruit: cantaloupe melon, strawberry, raspberry, blueberry, grape and even tree fruits such as lemon or apple using dwarf trees.

Aromatic plants: basil, coriander, mint, thyme, sage, tarragon, rosemary.

Advice for using hydroponics at home

Having a small hydroponic garden at home is relatively inexpensive and simple. We offer some tips to set up our own hydroponic urban garden:

• A plastic container is required about 30 cm deep, and a 10 cm tray that fits over it, with a drainage hole.
• An aquarium pump is placed in the bottom of the container, with the spout positioned to pump the water with nutrients into the upper tray.
• The plants are placed in small plastic containers on a substrate made of coconut fibre or rock wool.
• The container is filled with water with nutrients, which will have to be replaced every week or so.
• The entire unit is placed in a sunny place or under growth lamps.

Types of hydroponic crop systems.