A guide to hydroponic methods, appropriate substrates and vital nutrients.

Hydroponics applies various techniques of horticulture that involves growing plants without soil by supplying the roots with water based mineral nutrient solutions that brings about vigorous increase of their organic substance. Sub irrigation or top irrigation in a controlled artificial environment is employed, calling for the use of greenhouses, polytunnels and other indoor contained environments.

The increased amount of oxygen available in the rhizosphere and readily accessible by roots largely contributes to the success of hydroponic crop cultivation. Terrestrial or aquatic plants are grown with their roots exposed to an amendable nutritious liquid, depending on individual plant needs, freely or supported by an inert medium.

Sophisticated grow rooms allow growers to further increase productivity by manipulating the plant’s environment like providing extra carbon dioxide, beyond elongated periods of photosynthesis with artificial lighting, reduced pest problems, increased oxygen in the rhizosphere, constant amounts of nutrient feed within reach of the roots, temperature control, moisture availability and the ability to produce crops all year round.

Despite the media being inert, roots can cause pH changes to the rhizosphere and root exudates such as secondary metabolites can disturb rhizosphere biology and the physiological balance of the nutrient solution which needs to be constantly monitored and adjusted.

Nutrient rich solutions include dilutions of inorganic hydroponic solutions or organic hydroponic solutions of organically sourced macronutrients and organically sourced micronutrients.

Hydroponic cultures offer as advantages agriculture with

• a decrease in water usage compared to field cultivation,
• the highest biomass and protein production compared to other plant growing substrates like soil, with cultivation in the same environmental conditions and using the same amount of nutrients,
• space optimization where plant density per area, vertical growing and advanced technologies maximize the use of limited space,
• resource management whereby besides saving water, fertilizer solutions are contained, can be recycled and kept out of the natural environment,
• the use of pesticides is eliminated,
• there is no need for tilling or weeding,
• susceptible species can be shielded from climatic extremes, pests and diseases. 
  
  
  The following highlights the various types of hydroponic techniques and the equipment employed:

1. Static solution culture involves plants grown in containers with the the nutrient solution sitting still. The solution may be gently aerated with the help of aeration pumps or un-aerated. The un-aerated, the nutrient rich solution is kept low enough so that sufficient root surface area is exposed to ample oxygen circulation above the solution level. The reservoir, especially if made of clear material, is kept covered to avoid phototropism and minimize evaporation. Individual holes for each plant allow planting which aids with plant support. Reservoirs may be dedicated to  single or several plant species. Reservoir size may be increased as plants grow so that rotating space is available to start on the next batch of seedlings. The nutrient solution is changed or replenished either on a set schedule or when the concentration of nutrients drops to a preset number, measured with an electrical conductivity meter. Water or fresh nutrient solution is also added when the solution depletes below a certain level, a Mariotte’s bottle or a float valve can be used to automate maintaining the solution at a set level.
   
   
   

   Bare roots floating in a nutrient rich static culture solution.

   
   A variation is raft solution culture where plants are supported by a buoyant plane floating on the surface of the nutrient solution so the roots are always exposed to the nutritive liquid and the solution level dropping below the roots does not have to be monitored.
   
   
   

   Lettuce growing supported by a raft floating on the surface of nutrient rich culture solution.
   
   

2. Continuous flow solution culture employs a constant flow of nutrient solution past the roots. This hydroponic technique is easier to automate than the static method as sampling and adjustments to temperature, pH and nutrient concentrations can be made in an individual large storage tank that serves thousands of plants. A downside is that the continuous flow method has little buffering against flow interruptions such as in the case of a power outage, a back up battery or a gas generator is a good addition.
   
   
   

   Illustration on the flow of soluble nutrients diluted in water into a continuous flow solution culture hydroponic system and back out allowing for analysis and changes before being recirculated.
   
   

A popular highly efficient variation is the nutrient film technique, NFT, where a very shallow stream of water containing the dissolved water-soluble nutrients is continuously circulated past bare root mats of plants in a watertight channel with the upper surface exposed to air. NFT thus delivers an abundant supply of oxygen to the roots of the plants, the nutrient levels can be effortlessly sustained along with profuse water flow, leading to larger yields of high quality produce over extended periods of crop harvest as a result of all three requirements for healthy plant growth being achieved. To ensure consistency the principles of NFT should always be practised based on using the right channel slope, flow rate and channel length. Slopes of 1: 30 to 1:40 are recommended to reduce ponding and water logging to a minimum. A one litre per minute flow rate is advocated, with half the rate at planting and later increased up to a maximum of 2 L/min. Faster flow rates result in nutritional problems in cultivated plants. Channel length should not exceed 10 to 15 meters as nitrogen depletion over the length of the channel has been observed on rapidly growing crops. To solve channel length limitations, nutrient feeds may be placed every 12 meters along the conduit and halving flow rates through each outlet.

Simultaneous cultivation two species of green and red oakleaf lettuce, basil, bok choi and spinach using a nutrient film technique NFT hydroponic system showing the free flow of benefitting oxygen through open channels.

5. Aeroponics delivers a continuous or discontinuous allowance of fine liquid droplets of nutrient solution to plant roots suspended, without the use of a substrate, in a deep air growth chamber so that the rhizosphere environment is always saturated with a fine mist of atomized nutrients and receives excellent aeration. Aeroponic systems are studied by NASA as a mist is more effective to handle than a liquid in zero gravity environments in space. Their research has shown that aeroponics uses 65% less water than water intensive hydroponics to give a significant 80% increase of essential nutrients measured in dry weight biomass. A comparative quarter of nutrient input is needed and aeroponic grown plants do not suffer transplant shock when planted into soil. Aeroponic systems offer the ability of reducing the spread of disease and pathogens as the microenvironment of this cultivation set up can be finely controlled. The 100% receipt of available oxygen and carbon dioxide to the suspended plant root zones, stems and leaves contributes to the acceleration of biomass growth and reduced rooting time. Some plants can only survive for so long in water before they become waterlogged giving aeroponics the advantage of being able to grow any plant species. Aeroponics are therefore used in laboratory studies of plant physiology and pathology. Aeroponics is a successful agriculture technique for commercially crucial propagation, seed germination, seed potato production, tomato, melon, cucumber, brassica, squash, beetroot cultivation, leaf crops, herbs and micro greens.
   
   
   

   Aeroponics plant support structure lifted to show nutrient rich solution being supplied to seedlings of the aromatic culinary fine herb basil in the form of aerosol in an enclosed rhizosphere space under controlled laboratory conditions.
   
   

6. Fogponics or atmoponics dispenses nutrient solution aerosolized into much smaller particles of enriched water using a diaphragm vibrating at ultrasonic frequencies, compressed air or heating elements. Droplets of 5 to 30 μm in diameter form a suspension, diffusing through the air with more ease to deliver nutrition to plant roots without limiting their access to precious oxygen. Plants best absorb particles in sizes of 1 to 50 μm; absorption rates are amplified and amount of energy required for nutrient acquisition thus growth is reduced.
   
   
   

   Potatoes grown using Fogponics instruments, perceived by the delicate mist surrounding the root tips, to create a constant humid, nutrient rich environment with an abundance of oxygen that allows for efficient root uptake and results in faster plant growth. 
   
   

7. Passive sub-irrigation, passive hydroponics, semi-hydroponics or hydroculture is a method where plants are grown in an inert porous medium that moves water and fertilizer by capillary action to the roots from a reservoir without the use of a liquids recirculating system. In the simplest variation the pot containing the plant held in porous substrate sits in a shallow water based dilution of essential nutrients or on a capillary mat saturated with nutrient solution. The outcome is reduced labour input, the reduction of root rot and a constant supply of water is provided to the roots and hydroponics media containing more air space than traditional potting mixes, soil, peat moss or bark, delivering an increased amount of oxygen to plant roots. 
   
   
   

   Orchids grown in an organic aggregate, coconut husks, allowing more oxygen to reach the roots, crucial for epiphytic plants, with a bottom feed of enriched culture water at the base of the net pots. The aggregate is responsible for moving the nutrient rich solution from the reservoir to the roots in a passive hydroponic format.
   
   

8. Ebb and flow sub-irrigation or flood and drain hydroponics is a practice where nutrient enriched water is pumped to fill a container, where plants are growing in a porous aggregate, at regular intervals automated by a timer and the solution subsequently drains back into a reservoir. The  medium is thus regularly kept well supplied with nutrients and air. A versatile variety of substrates can be used with highly water retentive media requiring flooding only once a day and two to six waterings for others. The need for aeration is eliminated. The nutrient solution should be monitored for ideal concentration and pH.
   
   
   

   Lilium cultivation using ebb and flow hydroponics with plants sitting in pots filled with neutral porous mixed media that anchors the roots, allows maximum exposure to oxygen and act as a temporary reserve of nutritive water. The hydroponic solution alternately floods the system to briefly dampen the root zone and ebbs away.

   
   
9. Run to waste or Bengal system calls for either periodical application of nutrient rich solution to the inert growing medium manually one or more times a day or automated with a delivery pump, a timer and irrigation tubing to deliver the hydroponic solution with a frequency governed by plant size, growth stage, substrate retention and conductivity, ph, water content and climate. Watering frequency in multi factorial commercial settings is adjusted by computers and programmable logic controllers, PLCs. Large agricultural crops like tomatoes, cucumbers and peppers often employ the use of run to waste hydroponics.
   
   
   

   A manual run to waste hydroponics operation for the cultivation of micro greens where a tap is periodically opened to let out nutritive solution from the reservoir.

   
   
10. Deep water culture DWC, deep flow technique DFT, floating raft technology FRT or raceway hydroponics entails plant production by means of suspending the roots of plants through a net pot or freely supported by the raft into a nutrient rich, oxygenated water solution. An air pump combined with porous stones saturates the liquid with oxygen. The high amount of oxygen received by the roots makes the plants grow much faster. The tank is shallow, not more than a foot deep and pumping water to flow through pipes for distribution is not needed.
    This simple set up makes for ease of harvest and is employed by major produce growers to grow non fruiting fast growing short term nutrient hungry crops like leafy greens and herbs en masse.
    
    
    

    Young roots just grown enough to reach the nutritive hydroponic culture solution of a deep water culture set up with pump aided oxygenation discerned by the profusion of rising air bubbles.

    
    The Kratky method describes similarly growing plants with roots simply suspended in a reservoir of nutrient water without circulation. This one is a passive hydroponics method.
    
    
    

    The Kratky method is a simple home application of growing plants with roots suspended in nutrient culture in Mason jars or forcing bulbs in water.

     
    A variation is top fed deep water culture, Recirculating Deep Water Culture RDWC or bubbleponics, where highly oxygenated nutrient solution is constantly pumped from the reservoir to be delivered directly up to the roots. The water released over the plant root system subsequently runs back down into the reservoir to be recirculated to ensure a steady supply of oxygen and nutrients . An airstone pumps air into the reservoir. Both the water pump and the airstone run 24 hours a day. The larger volume of water used mitigates rapid changes in temperature, pH, electrical conductivity and composition of nutrients in solution.
    Increased plant growth during the first few weeks is experienced with top fed water culture when compared to deep water culture; the latter poses a time where the roots have not yet reached the solution. Roots get access to the nutritive water from the very beginning when grown in a top fed deep culture. Grow time is thus reduced by a few weeks even if growth standards out when roots are grown enough to reach the deep water culture reservoir.
    
    
    

    Cannabis medicinal plants grown in a top fed deep water culture Dutch Bato Bucket hydroponic configuration, illustrating pipes delivering oxygenated nutrient solution to the root systems from the top down. The nutritive solution then empties out of the individual plant pots into a collective drain channel back to the reservoir where the water is to be tested, amended, oxygenated and recirculated.

    
    
11. Rotary hydroponics structures are being developed using circular frames to continuously rotate around the centred high intensity grow light during the entire growth cycle of the cultivated plants. The plants are periodically watered with the nutritive hydroponic solution as they rotate. Rotary systems have been found advantageous for both home cultivation hydroponic gardens and commercial agriculture for allowing more plants to be grown per area of space and because of the continuous fight against gravity, plants mature more quickly than when being grown in soil or using other types of hydroponics techniques.
    
    
    

    Spinach growing in a rotary hydroponics structure, revolving around an ever present artificial light source. 
    
    

12. Vertical farming describes crops grown in stacked vertical and horizontal layers using the soilless agriculture techniques of hydroponics, aeroponics and aquaponics. Cultivation often takes place in indoor, controlled environments allowing all season, year round high value fruit and vegetable production by limiting weather disruptions especially in sub arctic regions and other parts of the world with long cold winters. Closed environments in are in addition adjustable for light, carbon dioxide, humidity introductions, optimizing plant growth. A larger amount of food cultivation is possible per unit area of land along with amplified crop yields and the ability to grow more varieties of crops together facilitated by amendable culture solutions. Renewable energy sources should be used to meet light, pump and aeration large energy demands to assuage costs. The reduced requirement for farmland is less disruptive to native flora and fauna helping nature conservation efforts.
    
    
    

    Commercial cultivation of tomatoes demonstrating enhanced crop quality in the contained environment of a polytunnel, vertical farming, hydroponics and an artificial light source.

    
    
    Plant growing medium, often called hydro stones, used with or without net pots, comes from various sources and materials, some more porous, inert or chemically inactive, pH neutral, water wicking or retentive, degradable and reusable than others.
    
    

    Lettuce growing freely in a net pot. Roots are bare, no aggregate is employed.
    
    

• Rock wool or mineral wool is a bundled up fibrous material of spun molten rocks, basalt, slag and minerals. This medium is inert, resistant to microbiological degradation, provide mechanical structure to stabilize plants, capable of capillary action for liquid nutrient uptake, can be engineered to hold large quantities of water and air and is conditioned to be rendered neutral from its naturally high pH by soaking in a solution adjusted to pH 5.5 until it stops bubbling. The efficiency and effectiveness of mineral wool makes it the most widely used substrate in hydroponics, suitable for both commercial recirculating systems or run to waste methods. Rock wool is preferred for the seedling or new cutting stage and can remain with the plant base for its lifetime. Handle with care to prevent skin abrasion while handling mineral wool. 
  
  

  The ease of transplanting when the need of potting up arises is shown by this mineral wool application.
  
  

• Lightweight expanded clay aggregate, LECA is optimum for hydroponic establishments where accuracy of the nutrient content in the water solution is important. Hydroton is made from clay fired in rotary kilns at 1200 °C so it expands into round pellets and becomes porous. The baked expanded clay pellets are light, inert, pH neutral, do not contain any nutrient value, allow drainage, promote increased oxygen levels available in the rhizosphere, does not decompose and gradually wick up moisture and nutrients to be readily retained until saturation allowing consistent nutritive solution uptake by the plants. LECA balls are made into different sizes and densities with manufacturing adjustments as the heating process causes gases trapped in the clay to expand to form thousands of small air bubble pockets that results in a porous structure. High density LECA offers greater strength and lower density LECA provides more buoyancy for floating applications. Ecologically sustainable exclay may be used with recirculation or standing nutrient solutions and can be re-used after cleaning and sterilization with white vinegar, chlorine bleach or hydrogen peroxide then rinsed completely, provided root growth has not entered inside the medium to undermine precision, find out by breaking open an aqua clay pebble after use. 
  
  Seedlings sprouting in a recirculating hydroponic structure with LECA used as growing medium.
  

• Growstones are made from glass waste made up of 0.5% to 5% calcium carbonate and soda lime glass. Growstones retain more air and water than perlite and peat and hold more water than rice husks.
  
  A top fed hydroponic system employing growstones as substrate.
  

• Coconut coir or coir peat is a byproduct of coconut processing. Although a biological product, before becoming a viable growth medium, coir must undergo a maturation process that involves time and substantial amounts of water to wash out accumulated salt, tannins and phenolic compounds as coconuts absorb high levels of nutrients during their life cycle. Coconut coir has impressive water retention capabilities. The dry, chunky fibrous material’s capacity is demonstrated when it expands up to four times its size when exposed to water. Coconut coir is resistant to pests and diseases and offers optimized growing conditions compared to inorganic rock wool.
  
  

  A young squash seedling growing in coconut coir medium in a top fed hydroponic installation.

  
  
• Parboiled rice husks, PBH are the agricultural byproduct of rice dehusked using steam. Rice hulls are an organic material that decompose over time, allow drainage and retain less water than grow stones. Rice husk do not interfere with plant growth regulators; plant hormones or phytohormones produced by every cell plant to control all aspects of plant growth and development.
  
  Barley germination in a top fed hydroponics system using parboiled rice husks as growing medium.
  
  
  
• Perlite is an amorphous volcanic glass that expands into a non renewable lightweight material when heated the high content of trapped water vaporizes and escapes when it is superheated to 900 °C. Perlite provides thermal and mechanical stability for hydroponic plants, is buoyant, resists microbial attacks and organic solvents and decreases  soil density in differing quantities to prevent compaction when used as an amendment due to its high permeability and low water retention. Perlite provides more aeration and holds less water than vermiculite. Perlite contains a high amount of fluorine that could be harmful to some plants, impart in some research before use. 
  
  

  A major hydroponics cultivation facility employing the use of vermiculite sitting atop a nutrient solution reservoir for germination.

  
  
• Vermiculite is a hydrous phyllosilicate mineral that undergoes exfoliation and significant expansion when superheated. The resulting light pebbles have a natural wicking property that allows them to draw water and nutrients from a reservoir up to plant roots in a passive hydroponic system. Vermiculite holds more water than perlite; if too much water and not enough air surrounds the plant roots, the water retention capacity of the medium may be reduced by mixing in increasing amounts of perlite. 
  
  

  Fig plants fruiting in a recirculating hydroponic set up using perlite as aggregate.

  
  
• Pumice is a naturally occurring vesicular rock resulting from volcanic activity. Pumice varies in density according to the thickness of material between the bubble pores, many samples float on water with a porosity of 64% to 85% by volume. The porous quality of pumice allows the easy exchange of gases like oxygen and carbon dioxide beneficent to plants. The fragments of volcanic glass pumice is light, pH neutral, and inorganic thus does not decompose over time, nor does it attract or host fungi and insects.
  
  Tomato vines growing in a dutch bucket hydroponic system with pumice used as growing substrate.
  
  
  
• Sand is easily available however is heavy, does not hold water very well and needs to be sterilized between uses. 
  
  

  Sandponics using sand as aggregate, a technique often employed in deserts accompanied with aquaculture to provide essential nutrients for plant feed, called aquaponics.

  
  
• Gravel may be obtained from various sources, provided it is washed before use, including aquatic ones, is easy to keep sterile, drains well and does not become waterlogged. Plants growing in a traditional gravel filter bed with water circulated by electric powerhead pumps are in effect using the gravel hydroponics method termed nutriculture. Gravel is heavy and is prone to drying out along with plant roots if a continuous supply of water is not provided.
  
  

  Gravel used at the very beginning of a horticulture cycle, seed sprouting.

  
  
• Wood fibre and Fibralur are wood shavings, byproducts from sawmill residues. An efficient organic substrate for hydroponics that keeps its structure for a very long time, wood wool, excelsior or wood slivers have been used since the earliest days of hydroponics research. Wood fibres may however negatively impact plant produced growth regulating hormones. 
  
  

  Strawberries grown in an aggregate of wood fibres.

  
  
• Sheep wool obtained from shearing is a promising renewable growing medium that exhibits  a 70% greater air flow capacity that decreases to 43% with use and a 23% water retention capability that increases to 44% with use when compared with rock wool, coconut fibre, perlite and peat slabs. Sheep wool demonstrated increased yield out of all the tested substrates. The application of a biostimulator consisting of humic acid, lactic acid and Bacillus subtilis improves yields in all substrates.
  
  

  Brassicae seeds sprouting on organic sheep wool aggregate.
  
  

• Brick shards have similar properties as gravel but may alter the pH of the nutrient solution and requires extra cleaning before re use. Brick shards have similar properties as gravel but may alter the pH of the nutrient solution and requires extra cleaning before re use.
  

  Brick shards used to grow damp soil loving daisy. Edible flowers are employed in sweet and savoury recipes, to delicately garnish food and dried to brew tea. Hydroponics structures may be set up in regulated indoor settings or in the sunlight outdoors.

  
  
• Polystyrene packing peanuts and expanded polystyrene foam sheets are readily available and float on water. Polystyrene peanuts provide excellent drainage, they are mainly used in closed tube systems but can be too lightweight for some hydroponic application and non-biodegradable ones must be used as biodegradable ones will decompose into a sludge. However, plants may absorb styrene and pass it to consumers, a possible health risk. Expanded polystyrene foam are used as deep water culture rafts and often come pre cut to be fitted with net pots with or without substrates, mineral wool plugs or plants can be suspended without additional support.
  

  A commercial agricultural facility using expanded polystyrene foam for deep water culture cultivation rafts.

   
• High density polyethylene, HDPE floating rafts made of hard plastic offer superior strength and durability than polystyrene ones and made of a non toxic, more food safe and eco friendly material. HDPE rafts last longer as they can be cleaned and reused countless times. HDPE can be used to grow plants at temperatures above 24 °C. HDPE rafts are adapted to be suited substrate plugs or substrate free high density cultivation. The composition of essential and non-essential nutrients in both soil agriculture and hydroponic cultivation should be adjusted to satisfy Liebig’s law of the minimum. Liebig’s law is specific to every plant variety and states that growth is dictated not by total resources available but by the scarcest resource. Increasing the amount of all nutrients does not result in change but increasing the amount of the limiting nutrient, in relation to need or the one that the plant uses the most and renders scarce, results in improved plant growth and crop yield.
  
  

  High density polyethylene raft supporting collard greens floating on top of nutrient enriched culture solution.

  
  
  

  The composition of essential and non essential nutrients in both soil agriculture and hydroponic cultivation should be adjusted to satisfy Liebig’s law of the minimum. Liebig’s law is specific to every plant variety and states that growth is dictated not by total resources available but by the scarcest resource. Increasing the amount of all nutrients does not result in change but increasing the amount of the limiting nutrient, in relation to need or the one that the plant uses the most and renders scarce, results in improved plant growth and crop yield

  Micronutrients are chemical elements needed in trace amounts for normal plant growth and development.
  Macronutrients are chemical elements needed in large amounts essential for plant growth. 

Nutrient solutions are constantly tested along with plants periodically monitored for nutrient deficiency symptoms so that nutritive values of growing solutions may be correspondingly adjusted.

Hydroponic plant culture  solutions are made from dissolved water soluble nutrients in the form of inorganic salts, organically sourced fertilizers and additives.

A. Inorganic hydroponic solutions are formulated according to plant nutrition chemistry.

Inorganic nutrients are compounds that contain no carbon-hydrogen bonds and are not extracted from organic matter. For perspective, water is an inorganic compound as are the minerals in soil that plants draw up their roots in nature.

Nutrients that make up inorganic culture solutions are produced for horticulture fertilization by mining mineral salts, rocks and ores formed by natural geological processes that are treated and purified into singular minerals, industrially synthesized from chemical material available in nature, often in gas form, or chemically isolated from naturally occurring complex compounds.

• Diluting nutrients in their pure elemental and compound form allows for a high level of control over culture solutions adaptive to individual plant needs.
• Nutrients are favourably bioavailable to be readily uptaken by roots in comparison to organic nutrients that might need to undergo biodegradation with the help of microorganisms first.
• Hydroponic nutrient solutions do not have the cation exchange capacity, CEC of soil made up of clay particles and organic matter. The absence of CEC and soil pores renders pH, oxygen saturation and nutrient concentrations of hydroponic systems susceptible to rapid changes.
• The selective absorption of certain nutrients by plants often imbalances the amount of counter ions in the solution, impacting membrane potential, causes rapid pH change and affects the absorption of nutrients of similar ionic charge.
  Amongst other cases, this often happens on account to nitrate anions consumed rapidly by plants to form proteins, leaving an excess of cations in solution resulting in deficiencies of other cation based nutrients like Mg²⁺ even when an ideal amount of all nutrients are dissolved to form the solution.
• The pH of the solution and the presence of water contaminants may cause nutrients like iron to precipitate from the solution and become unavailable for absorption by the plants. Routine pH analysis and adjustments, buffering the solution or the use of chelating agents is necessary.
• Hydroponic solutions are usually standardized and require regular readjustments. Growth facilities are maintained under controlled laboratory conditions. Culture solutions are sustained at a near neutral pH of 6.0 and aerated with oxygen. Water levels are periodically refilled to account for transpiration losses and nutrient solutions require refortification to correct nutrient imbalances as plants grow and deplete nutrient reserves.
  The regular measurement of nitrate ions os used as a key parameter to estimate the remaining concentration proportions of other essential nutrient ions to restore the solution balance.
• Optimum concentrations of nutrients to be diluted in water for the preferred nutrition of each plant variety comes empirically from personal observation, sensory experience and experimental evidence, plant tissue tests and validated balanced standard solutions like the Hoagland solution, the Long Ashton nutrient solution or the Knop solution.
  
  Requisite concentrations of individual nutrient ions for general unspecific plant production. Solutions are mixed with all necessary nutrients to have total concentrations between 1000 and 2500 ppm. Tabulated concentrations of essentials nutrients below the specified ranges leads to nutrient deficiencies while exceeding the ranges leads to nutrient toxicity:
  

B.  Organic hydroponic solutions call for nutrients derived from plant material, i.e., compost, peat, fermented liquid plant manure, humid acid, seaweed extracts, wood ash and worm compost tea, animal waste, i.e, aged manure, liquid manure slurry, guano, and animal sourced husbandry byproducts and naturally mined minerals originating from fossil products of animal activity, i.e., anaerobic marine deposits greensand, fossil shell deposits limestones, fossil guano rock phosphates, raw Langbeinite, rockdust and unprocessed natural potassium sulfate.

Biological farming employs the use of naturally produced organic fertilizers. For context, fertilizers are materials applied to growing substrates to provide nutrients for plant growth distinct from liming substances which are used to raise the pH of growth material; culture solution or soil, in order to stimulate microbial growth that in turn increases biological processes enabling nutrients to flow more freely so they are more accessible to plants resulting in increased plant health and mass.

Ecological agriculture introduces some challenges that need to be resolved and precautions taken for successful hydroponic plant cultivation;

• Nutritional compositions of organic fertilizers are highly variable in terms of minerals and organic and non organic chemical species.
  Even similar materials can significantly differ in nutrient constitution based on their source, e.g., the quality of manure depends on the animal’s diet.
• Because of the varying and unknown amounts of nutrients present in biological materials, analysis is needed to identify available nutrients so amendments can be made. Besides additions, macronutrients and micronutrients may need to be sourced from different origins.
• Organic fertilizers coming from animal byproducts carry serious concerns of disease transmission in cases of plant contamination when cultivated for produce for human consumption and livestock forage.
• Biological fertilizers are in many instances particulate instead of soluble forms and may clog substrates and growing equipment.
  Milling and sieving organic materials to fine dust is necessary.
• Structural, enzymatic and metabolic biochemical degradation of organic fertilizing materials is needed beforehand so their mineral ingredients are made bioavailable to plants.
• Many organic molecules need oxygen for aerobic degradation, a gas essential for cellular respiration in the plants under cultivation, in addition to some materials further degrading under anaerobic conditions, particularly animal based ones to emit foul odours. 
• Fresh manure contains a big amount of ammonia that harm plants by burning the roots, bacteria from the animal’s gut are harmful to essential microorganisms that help with biodegradation and seeds that pass through unharmed present the risk of introducing weeds to the cultivation. Manure thus requires a period of drying, aging and composting so it is broken down and decomposed into a stable organic material before use.
• Careful organic sourcing of animal based fertilizers is required as animals need to consume organic food for the manure and byproducts to be organic. Harmful substances in feed from fields treated with herbicides along with de wormers will pass through the digestive tract of the animals and remain unchanged in composted manure piles for long periods of time. These substances affect substantial staple crops by causing deformities and poor to non existent yields and harm beneficial organisms.
• Organic compounds like sugars and vitamins are not necessary for normal plant nutrition.

1. Organically sourced macronutrients percentage average nutritional content per dried mass of materials:
   

2.  Organically sourced micronutrients are also sourced from organic fertilizers, e.g., composted conifer bark is rich in manganese and pulverized unrefined minerals, e.g., gypsum, calcite and glauconite.



C. Additives are supplementary compounds that may be added to both conventional and organic hydroponic culture solutions to boost nutrition acquisition and uptake in plants:

• Chelating agents and humic acid additions to regular nutritive solutions increase nutrient uptake.
• Rhizobacteria, PGPR, promotes plant growth, benefitting development and nutrient acquisition.
  Some PGPR increase nitrogen fixation.
  The bacterium genera Azospirillum and Azotobacter help maintain mobilized, bioavailable forms of nitrogen in hydroponic systems with higher microbial growth in the rhizosphere.
• Accumulations of nitrate in high concentrations is observed in plant tissue at harvest. Rhodopseudo-monas palustris adds to efficiency of nitrogen usage, increases yield and decreases nitrate concentration in plant tissue at harvest by 88%.
• Bacillus spp., Pseudomonas spp. and Streptomyces spp. convert forms of phosphorus that are not bioavailable to plants into soluble anions by decreasing pH therefore releasing phosphorus bound in chelated form rendering the element available in a wider pH range and mineralizing organic phosphorus.
• Bacillus inoculants allow hydroponically grown plants to overcome high salt stress that would otherwise reduce growth, beneficial to regions with high electrical conductivity or salt content in their water supply conducing to the need for reverse osmosis filtration systems to maintain high crop yield.
• CO₂ may be injected into the environments under controlled conditions of sealed greenhouses to contribute to improved growth and plant fertility.
  

This is almost brief information gathered on hydroponics plant cultivation. Keep an eye out for details on each type of system, equipment needed and nutrients. If you have questions of any comprehensive nature, send us an email. Aquaponics, where hydroponic plants receive nutrients from aquaculture; aquafarming of aquatic organisms of value, animals and plants like fish, crustaceans, mollusks, algae, decorative submerged and floating plants and lotus, in freshwater, brackish water and saltwater of the sea or lagoons under controlled or semi natural conditions like pisciculture and mariculture will be covered in subjects to come. Happy growing!

Alia B. M.
Biologist
evergreenbotany.com
evergreenbotanyglobal@gmail.com