Growing plants without soil, using water containing dissolved mineral nutrients, is called:

Hydroponics is a method of growing plants without soil, in which the roots are supplied with water containing all the essential mineral nutrients. The word comes from the Greek "hydro" (water) and "ponos" (labour or work), meaning "water working".

How hydroponics works:

• Plants are grown in water-based nutrient solutions, either with their roots directly in the solution or supported by an inert medium such as perlite, rock wool, clay pebbles or gravel.
• The nutrient solution provides nitrogen, phosphorus, potassium and other elements that plants normally take from the soil.
• The levels of nutrients, acidity (pH), light, temperature and oxygen are carefully controlled.

Common hydroponic systems:

• Nutrient Film Technique (NFT): a thin film of nutrient solution flows continuously over the roots in channels.
• Deep Water Culture (DWC): roots hang in an oxygenated nutrient solution.
• Wick system, ebb and flow (flood and drain) system, and drip system.

Related soilless methods:

• Aeroponics: roots hang in the air and are sprayed with a fine nutrient mist.
• Aquaponics: combines hydroponics with fish farming; fish waste provides nutrients for the plants, and the plants clean the water for the fish.

Advantages:

• Uses much less water than soil-based farming (up to about 90 per cent less), because water is recycled.
• Crops grow faster and give higher yields in a small space.
• Can be practised in cities, deserts, on rooftops, in greenhouses and in vertical farms, where good soil is not available.
• Fewer soil-borne pests and diseases, and less need for pesticides.

Disadvantages:

• High initial costs and technical knowledge required.
• Dependence on electricity for pumps and lights.

Commonly grown crops:

Leafy vegetables like lettuce and spinach, herbs, tomatoes, cucumbers, strawberries and capsicum. It is also used to grow green fodder for animals.

History:

The term "hydroponics" was popularised in the 1930s by the American scientist William Frederick Gericke.

Why not the other options?

• ✗Organic farming uses soil and natural inputs, avoiding synthetic chemicals.
• ✗Terrace farming is cultivation on steps cut into hill slopes.
• ✗Shifting cultivation involves clearing forest patches and moving after a few years.