It uses water as the medium for providing nutrients to the plant roots and it is further sub divided into static water culture and continuous flow water culture. Water is filled in tubs or tanks in variable depths. Nutrients are added into the water when required. Plant roots are dipped in the nutrient solution. Generally bottom of the tanks are filled with stones of varying sizes to promote aeration. Air is pumped from external sources and this meets the oxygen requirements of plant roots that are hanging partly in the air and dipped into water at the same time.
In addition to stationary water culture, continuous water flow culture is also a popular technique now a days. In this system a thin film of nutrient full water circulates below the plant roots. Plants have access to nutrients and water all the time during their growth period. Since a small film of water flows below the plant roots, system is called nutrient film technique (NFT).
It is another technique of soilless agriculture where, the plant roots are suspended in the air and nutrient rich water is sprayed over the roots at specified intervals. In this method the roots are misted with a nutrient solution while remaining suspended in the air.
Solid Medium Culture:
It includes a solid medium for hosting the roots during their growth and development period. Soilless agriculture is largely done in solid mediums, also known as substrates. The materials for the substrates are carefully selected. The popular substrate materials are coco mass, gravel, perlite, rock wool, sand, wheat straw, rice husk etc. These are filled into plastic bags. The materials should properly hold water and also permit air passage for respiration of plant roots. The porous matter in the plastic bags facilitates air circulation.
The water is forced to flow through the pores of solid media. Solid growing medium is an inert material. Crushed coco shell without hairs is most popular, however the search for ideal materials still continuous. The nutrient water is applied several times a day and its frequency depends on the temperature and expected transpiration and evaporation rate.
Ground Coco Shells
The coco shells especially without fibers are ground and used as substrate for hydroponic farming. The coco shells are inert in nature and does not chemically react with the chemicals in the nutrient solution. There is always appropriate ratio of air and water in the coco material which helps in proper growth of plant roots. Coco also promotes cation-exchange that keeps storing minerals required by the plants. It is generally available in the form of coco peat. Coco waste material is packed in bags and is available with the coconut vendors in Pakistan.
Baked Clay Pellets
Pellets of clay soil are baked in rotary kiln at a temperature of 1200 oC. The pellets swell and become porous and they are also inert. They are round or nearly oval. They are quite light by weight and they do not squeeze with the time. The shapes and sizes of the pellets are varying. It can be reused after its sterilization. The pellets could be treated with vinegar, H2O2 or chlorine bleaching. These can be locally made and also reused.
Rice husk is received after milling the rice and it is used as medium for growing vegetables in soilless agriculture. It has a good water retaining property but its decaying property reduces water retention with the passage of time. It is easily available for commercial farming in Pakistan.
This is a mineral wool most suitable as a substrate for soilless agriculture. It has a best capillary movement of water. The material is costlier compared with other materials. It is used as seed plugs for raising seedlings, and plants during their early growth stage in rock wool boxes.
This is quite expensive but it can be successfully used because of larger air capacity of about 70 percent that reduces to 43 percent with passage of time. While water holding capacity increases accordingly.
It is very cheap, inert and easily available. It is quite heavy, water does not stick to gravel and therefore the plant roots can dry out soon.
This material is available everywhere on little cost. It has poor water holding capacity because of little cation exchange capacity of the sand grains. It must be sterilized for reuse.
It is superheated volcanic material in the form of bright color bits of varying sizes. This is commonly used as potting material by home gardeners.