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           HYDROPONICS

Hydroponics (From the Greek words hydro, water and ponos, labor) is a method of growing plants using mineral nutrient solutions, in water, without soil. Terrestrial plants may be grown with their roots in the mineral nutrient solution only or in an inert medium, such as perlite, gravel,  rockwool, or coconut husk.

Researchers discovered in the 19th century that plants absorb essential mineral nutrients as inorganic ions in water. In natural conditions, soil acts as a mineral nutrient reservoir but the soil itself is not essential to plant growth. When the mineral nutrients in the soil dissolve in water, plant roots are able to absorb them. When the required mineral nutrients are introduced into a plant's water supply artificially, soil is no longer required for the plant to thrive. Almost any terrestrial plant will grow with hydroponics. Hydroponics is also a standard technique in biology research and teaching.

Advantages

Some of the reasons why hydroponics is being adapted around the world for food production are the following:

• No soil is needed
• The water stays in the system and can be reused- thus, lower water costs
• It is possible to control the nutrition levels in their entirety- thus, lower nutrition costs
• No nutrition pollution is released into the environment because of the controlled system
• Stable and high yields
• Pests and diseases are easier to get rid of than in soil because of the container's mobility

Today, hydroponics is an established branch of agronomy. Progress has been rapid, and results obtained in various countries have proved it to be thoroughly practical and to have very definite advantages over conventional methods of horticulture. The two chief merits of the soil-less cultivation of plants are, first, much higher crop yields, and second, hydroponics can be used in places where in-ground agriculture or gardening is not possible.

Nutrient solutions

Plant nutrients used in hydroponics are dissolved in the water and are mostly in inorganic and ionic form. Primary among the dissolved cations (positively charged ions) are Ca2+ (calcium), Mg2+ (magnesium), and K+ (potassium); the major nutrient anions in nutrient solutions are (nitrate), (sulfate), (dihydrogen phosphate)

Numerous 'recipes' for hydroponic solutions are available. Many use different combinations of chemicals to reach similar total final compositions. Commonly used chemicals for the macronutrients include potassium nitrate, calcium nitrate, potassium phosphate, and magnesium sulfate. Various micronutrients are typically added to hydroponic solutions to supply essential elements; among them are Fe (iron), Mn (manganese), Cu (copper), Zn (zinc), B (boron), Cl (chlorine), and Ni (nickel). Chelating agents are sometimes used to keep Fe soluble. Many variations of the nutrient solutions used by Arnon and Hoagland (see above) have been styled 'modified Hoagland solutions' and are widely used. Variation of different mixes throughout the plant life cycle, further optimizes its nutritional value.[16] Plants will change the composition of the nutrient solutions upon contact by depleting specific nutrients more rapidly than others, removing water from the solution, and altering the pH by excretion of either acidity or alkalinity.[17] Care is required not to allow salt concentrations to become too high, nutrients to become too depleted, or pH to wander far from the desired value