Hydroponics derived from two Greek words hydro (water) and ponos (labour), aims at growing plants in mineral nutrient solutions without using soil as medium. The technique was discovered in the 19th century when it was concluded that plants absorb essential mineral nutrients as inorganic ions in the water. When the required mineral nutrients are supplied through water then soil is no longer required.
Hydroponics culture is an intensive method of raising any crop and protected conditions enhance efficiency of production. Nowadays flowers, foliage and bedding plants are cultivated in vertical gardening which is one of the easy methods of hydroponics.
Besides this growing high valued cut flower crops like orchids and anthurium, hydroponics is a precision method. Though hydroponics is practiced in tropical, sub-tropical and temperate regions, for temperate regions protected structures should have temperature control, reduce water loss by evaporation, and protect crops against the elements of weather like snow, wind or rain.
Experimental trials on hydroponics were carried out in France and England during the seventeenth century. Spearmint was first grown by John Woodward in England in water solution. Knop and Sachs (1861) in Germany introduced systematic study of plant nutrition in hydroponics and Gericke (1929) coined the word hydroponics and was first to introduce technique of growing plants in tanks of nutrient solutions by growing crops like beet, carrot, radish and potato.
Need of Hydroponics
• Urbanization and industrializations.
• Unfit soils at some places for cultivation.
• Hydroponics eliminates the need of soil and efficient water use efficiency.
This method does not allow solid medium for the roots and has no support for plants. In this method plant roots are exposed to nutrient solutions, without any type of growing medium and surplus solution is recovered, replenished and reused. Waterproof trough or benches of suitable material are constructed, wire grid fits closely over the top of the tank containing nutrient solutions where the grid serves as a support for the growing plants and roots descend through the mesh into the solution.
Static solution culture
Plants are grown in containers like glass containers, plastic buckets, tubs or utensils with nutrient solution. Reservoir size and number of plants depends upon plant size and number of plants grown per container. Change of solution is either scheduled and incase solution level drops below.
Continuous flow solution culture
Nutrient film technique where nutrient flow is continuous at root level and solution is amended as per the stage of plant growth and development. Advantage of the NFT system is that the plant roots are exposed to adequate supplies of water, oxygen and nutrients.
Aeroponics means an environment saturated with nutrient solution growing plants with their roots suspended in a deep air or growth chamber with the roots periodically wetted with a fine mist of atomized nutrients. Orchids are mainly grown in this type of system.
When soil less medium like coca peat, sand, gravel etc is used as a support for the root system then it is called medium culture.
Closed System: when the nutrient solution is recovered, replenished and reused.
Open System: when the nutrient solution is delivered to the plant roots and is not reused.
Baked clay pellets are suitable for hydroponics systems in which all nutrients are carefully controlled in water solution. The clay pellets are inert, PH neutral and do not contain any nutrient value.
Rock wool is an inert substrate, granular and has very high available water and aeration properties. It is slightly alkaline and has a negligible CEC.
Coco peat, the outcome of the outermost shell (bolster) of the coconut is 100% natural medium.
Perlite is a volcanic rock that has been superheated into very lightweight expanded glass pebbles.
Vermiculite is another mineral that has been superheated until it has expanded into light pebbles. Vermiculite holds more water than perlite and has a natural property that can draw water and nutrients in a passive hydroponic system.
Sand is cheap but heavy and it does not always drain well and needs sterilization between uses.
Gravel is cheap, clean, drains well and does not allow water logged.
Peat moss is light brown in colour and is decomposed.
Plant nutrients are dissolved in the water used in the hydroponics 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 nutrients are NO3 – (nitrate), SO42- (sulfate), and H2Po4- (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.
Hydroponic nutrients should be complete, containing every essential element, both major and minor, required by all green plants for optimum plant growth. The nutrient should be well balanced containing enough of all essential elements so no deficiency occurs, while not containing too much of any element that might lead to a toxicity. Also, the nutrient should be pH balanced and buffered, preventing the pH from drifting too high (alkaline) or too low (acid). The last and maybe most important requirement is that the nutrient solution be water soluble with minimal or no residue. The mineral salts used should readily dissociate into elemental ions and not contain any toxic chemicals or elements like heavy metals (lead, mercury or tungsten). This is controlled by the selection and purity of the raw ingredients used.
The pH value refers to the acidity or alkalinity of the nutrient solution. pH readings run from 0 to 14 (0-6 acidic; 7 neutral; 8-14 alkaline). The recommended pH level for a general hydroponic solution is between pH 6 and pH 6.5
(To be continued…)
(The Authors are Faculty, Division of FLA SKUAST-K Shlimar)