Hydroponics is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops, without soil, 

by using water-based mineral nutrient solutions in aqueous solvents. Terrestrial or aquatic plants may grow with their roots 

exposed to the nutritious liquid, or, in addition, the roots may be physically supported by an inert medium such as perlite, 

gravel, or other substrates.Despite inert media, roots can cause changes of the rhizosphere pH and root exudates can affect 

rhizosphere biology and physiological balance of the nutrient solution by secondary metabolites.