Hydroponics,
Hydroponics may simply be described as growing plants with nutrients and water, and without soil. The water must be delivered to the plant root system. The root system may hang directly in the nutrient solutions, be misted by it or can be enclosed within a container or a trough which is filled with a substrate [a replacement for soil] the substrate may consist of many different types of materials such as perlite, coir, expanded clay, vermiculite, pumice, gravel or rock wool. All substrates must provide good water holding capacity yet be porous for gas exchange. All substrates must provide good water holding capacity, but this is where insects and fungi live, thrive and damage plant root systems. In between watering, substrates become the storage location of water and nutrients for the plant root system and also food and shelter for insects and fungi. The roots grow within the substrate while securing the plant within the container or trough. This provides a fertile delta for insects and fungi that can only be treated with chemicals. Commercial and small scale agriculture can use organics or beneficial insects.
There are many techniques to deliver water to the plant root zone. For container grown plants each individual plant is provided an emitter for water in the form of a drip irrigation system. Water may be channeled to a continuous row of plants with in a trough, such as in the nutrient film technique system. A large tray of plants may be watered from below by filling the entire tray with water and then draining all excess water. This is called Ebb and flood irrigation. Water is typically recycled within nutrient film technique and ebb and flood systems. It is more difficult to recycle in a drip irrigation system and require additional equipment such as water, a sterilizer and fertilizer monitoring and adjustment equipment.