Hydroponic farming in the 21st Century

Hydroponic farming has transformed agriculture in its 4000 years of existence. From the transfer of mature trees to the King’s palace in Egypt to a fodder unit of a poultry farmer in the 21st century, hydroponic farming has come a long way.

In the 1970s researchers developed complete nutrient solutions paired with appropriate soilless media. They further studied how to optimise the levels of nutrients, water and oxygen making soilless media superior to soil in terms of yield.

Soilless media also have the advantage of eliminating disease organisms that need to be controlled; an impossibility with soil. The media can be disinfected before use and between uses ensuring a growing season free of disease. This type of farming has given farmers better control over crucial factors, leading to improved plant performance.

In this article we will learn what hydroponic farming entails in the 21st century, choice of hydroponic system and crop, nutrient solution and formulation and finally crop care, touching on pest and diseases.

What is Hydroponic Farming?

The term hydroponics was conceived by Gericke (1937) to mean growing plants in water without any substrate. The definition has since evolved to mean growing plants without soil, in a nutrient solution. The growing media that have replaced soil include mineral components such as pumice (volcanic rock), organic substrates such as coco coir (coconut husk) and peat moss.

Soluble fertiliser is mixed with water to form a nutrient solution that is used to provide nutrition to the plant. Conditions such as light intensity, water, temperature and nutrient availability are all kept at optimum levels.

A big determinant of nutrient availability involves two factors namely, pH and electrical conductivity (EC). pH is a measure of how acidic or basic a solution is and most nutrients are available to the plant at a pH between 5.0 to 6.0.

Electrical conductivity is the potential of any material to conduct electricity. The more ions (nutrients) dissolved in a solution the higher the EC. This gives the farmer a better understanding of ions in a solution and can feed the plant at an ideal quantity.

Choice of Hydroponic System and Crop

Is it a huge commercial farm in Central Appalachia, USA or a balcony in Nairobi City? Hydroponic systems offer options for seeking commercial gain, ornamental gardening or a kitchen garden for your family’s nutritional needs.

What we desire to achieve is not the only factor, the financial factor determines cost of materials such as the growth media, labour and transportation. To make your choice easier there are companies that provide ready-made systems, with packages that include transport, labour and consultancy services, for example, Hydroponics Africa.

Hydroponic farming has made choice of crop the least of a farmer’s worry. You can choose a system that is most favourable to the crop you want to grow. A system that will afford the crop needed anchorage, ease in nutrient provision and ease of harvest.

Types of Hydroponic Systems

Before we delve into the types an important point to have in mind is water. Availability and quality are very important in all types of systems. More on water will be discussed in the nutrition and crop care section.

Hydroponic technologies have advanced rapidly, leaving a variety of innovations to choose from. To capture all these technologies adequately requires a whole article which I will do later. For this particular piece, we will concentrate on two types that I have found common and easy to start with.

1. Drip irrigation systems

Drip irrigation systems deliver a spray, drip, or slow flow of irrigation solution directly to the top of the root zone. Water flow from the emitter may vary according to the needs of the plant, but in all cases the flow is slow. The slow rate is required to allow water move sideways on the root zone before water goes down the growth media profile.

Drip systems allow for precision and uniformity but at a steep cost making it not feasible for small pots. This system is appropriate for large-scale to medium-scale ventures. In this system, we can use grow bags filled with coco coir or troughs filled with pumice.

Drip system with coco coir filled grow bag

Drip System with pumice filled troughs

In such production systems, the irrigation system delivers a slow drip and this water moves relatively quickly through the substrate. Most substrates are porous, so it is essential to cut slits or holes into the base of the grow bag or trough to allow water to drain.

There are two categories of hydroponic drip systems: recovery and non-recovery. In recovery, the excess water is drained from the grow bed back into the reservoir to be reused during the next drip cycle. In non-recovery systems, the excess water drains out of the growing media and runs to waste.

2. Ebb and Flow systems

Ebb and flow systems or flood and drain systems are very popular hydroponic growing methods. This system is easily customizable. The grow bed or tube can be filled with a variety of net cups. Net cups are readily available on sale or you can choose to repurpose a 500ml or 300ml yoghurt cup by perforating holes on the sides.

The ebb and flow system allows you to experiment with your plants and media, and for this particular article, you will get an opportunity to learn how this system works in a vertical A-frame Structure.

Vertical A-structures can also be done with the nutrient film technique, which requires a thin film of nutrient-rich water to be pumped to the plants continuously. This technique is prone to human error and mechanical failure.

When pumping of water is disrupted, it can lead to oxygen shortage. A 10-minute shortage of oxygen can stop root growth and a 30-minute shortage results in the death of the elongated zone above the root tip.

A-structure Hydroponic system

As shown in the photos above an A-structure can be made with a metal or wooden frame. Grow tubes are then held in place with brackets fastened on both ends of the frame.

Piping is required to take water from a water tank/reservoir to the grow tubes which have holes perforated at intervals desirable for plant spacing. The roots and growth media are in contact with the nutrient solution that fills the PVC grow tube. When the water has soaked the growth media the excess is drained to the tank for recirculation.

The intervals of watering the plants vary with the temperature of a greenhouse or open space being used. Watering is done twice to thrice a day. One can observe how moist the substrate is, making sure at no point of the day the media is dry.

Mixing of nutrients and manipulation of pH is done in the water tank. Over-irrigation of the plant will lead to rot root due to lack of oxygen, so space watering intervals appropriately. Regulating the EC and balancing the pH is important to avoid toxicity caused by excess nutrients; more on this in the next part on nutrition.

Nutrition and Nutrient formulation

There are about 19 elements that are essential to plant nutrition. An essential element is one that is required for a normal life cycle of a green plant and whose role cannot be taken up by another element.

Macronutrients (required in large amounts) include carbon (C), hydrogen (H), oxygen (O), nitrogen (N), phosphorus (P), calcium (Ca), sulphur (S), potassium (K) and magnesium (Mg). Micronutrients (needed in small amounts) include chlorine (Cl), iron (Fe), manganese (Mn), boron (B), zinc (Zn), copper (Cu), molybdenum (Mo), sodium (Na), nickel (Ni) and selenium (Se). These elements will form the backbone of this section, so keep them in mind.

In soilless culture, it is important to supply these elements continuously because of the limited capacity of the medium to hold on to the nutrients. The rate of nutrient requirement and nutrient composition varies with the growth stage and this dictates how nutrients are formulated.

Formulation of nutrients

Plants feed on nutrients in a solution form, and this is achieved by mixing soluble fertilizer and water. This process is known as fertigation. The quality of water plays an important part in determining which kind of fertiliser should be used. Before choosing a fertigation plan, get your water tested.

Municipal water can be unsuitable because of high levels of chlorine and calcium. Surface water from rivers and lakes may also be of low quality because of human pollution and pathogens.

Rainwater is the best for agriculture because it is clean and has low EC (small amount of dissolved ions) providing a good solvent for fertilisers. Groundwater varies in quality but is a reliable source. All these sources are viable for farming only after testing is carried out.

Solution A and B solutions versus single and multi-element fertilisers

A particular nutrient recipe can be made for a specific crop in relation to the chemical composition of the water source. A system that is popular to this date was developed by Verwer (1978) where nutrient solutions A and B are mixed in water. The two solutions are diluted in fresh water to avoid precipitation (forming of an insoluble solid) in pipes and on the growth media.

Solution A usually contains calcium compounds and Iron, and Solution B contains sulphates, phosphate and chelated micronutrients. Procedure of application is as follows:

1. Add solution A to your feeding tank and stir until everything is dissolved.

2. Add solution B to your feeding tank and stir until everything is dissolved.

3. Make sure the EC is at the required level, 1200-1500 microsiemens during transplanting and 1800-2800 during flowering and fruiting stages.

4. Balance the pH by adding a food-grade acid or basic solution ensuring that it is never below 5.0 or above 6.5.

These measurements are made using an EC and pH meter. After all the results are satisfactory the nutrient solution can be pumped to the plants. The procedure may vary according to manufacturer specifications, so be flexible and keen on the instructions given.

Human error may lead to excess amounts of nutrients in the growth media. It is important to flush the system with freshwater or an oxidising agent like Hydrogen Peroxide. Hydrogen Peroxide can also be used to kill pathogens at a dosage of 0.05 per cent against Pythium and 0.01 per cent against other fungi such as Fusarium.

Single and multi-element fertilisers

During recent years fertilisers have evolved from single or multi-element fertilisers such as calcium nitrate, Potassium sulphate and monopotassium phosphate to a more sophisticated combination of elements. This sophistication is necessary to fine-tune nutrition for a specific growth strategy.

Manual calculations of the recipe have been replaced by computerised calculation and commercial injector systems. How do these systems work?

• A mixing tank is connected to the various fertiliser stock tanks.

• In the storage tanks, solid fertilisers are dissolved in water and diluted at a standard high concentration.

• Quantities of the highly concentrated fertiliser solution are fed into the tank of the nutrient dispenser system.

• They are then mixed in accordance with a recipe, diluted with fresh water to a suitable concentration for the plants and finally pumped to the crop in the greenhouse.

Macro and Micronutrients and their Benefits

Element	​Benefit
​Nitrogen	Nitrogen is necessary for chlorophyll synthesis and, as a part of chlorophyll molecules, is involved in photosynthesis.
​Phosphorus	Phosphorus promotes root development, early seedling growth, increased stalk and stem strength, and improved flower formation and seed production.
Potassium	​ Has important effects on factors such as size, shape, colour, taste, shelf life, fibre and other quality-related measurements. Ample potassium can increase root growth and improve drought tolerance.
​Calcium	​Calcium improves root and leaf growth, stimulates microbial activity, molybdenum (Mo) availability, nitrogen fixation and uptake of other nutrients.
​Magnesium	​Magnesium acts as a phosphorus carrier in plants and is required for better root formation.
​Sulphur	​Required for synthesis of certain amino acids and is a constituent of chlorophyll.
​Boron	​Boron improves seed set under stressful conditions and is a component of all cell walls in the plant.
​Chlorine	​Chloride is key in stomatal regulation and transport of nutrients such as calcium, magnesium and potassium.
​Manganese	​Manganese plays a vital role in photosynthesis by aiding in chlorophyll synthesis.
​Iron	​Iron is a catalyst to chlorophyll formation and acts as an oxygen carrier in the nodules of legume roots.
​Nickel	​Important in plant nitrogen (N) metabolism.
​Copper	​Copper is necessary to chlorophyll formation in plants and catalyzes several other plant reactions.
Zinc	​Protein synthesis and growth regulation require Zinc.
Molybdenum	​Required for the synthesis and activity of the enzyme nitrate reductase. Molybdenum is vital for the process of symbiotic nitrogen (N) fixation by Rhizobia bacteria in legume root modules.
​Hydrogen	​Hydrogen ions are vital in both aiding proton gradients to help drive the electron transport chain in photosynthesis, and for plant respiration.
​Oxygen	​Responsible for cellular respiration in plants. This element plays a critical role in photosynthesis and is both stored for energy and released as a by-product.
​Carbon	​Carbon is the primary energy source and building block for plant tissues.

• It is important to note that nutrient need is determined by the stage of growth.

• Nutrient needs vary per crop, for example, corn/maize takes up phosphorus continually during the growing period and in large proportion during the grain filling stage but wheat, on the other hand, takes all the phosphorus needed by day 100 of growth and in the last 40 days of growth.

Pest, Diseases and Crop Care

Seven Principles of Plant-pest Control

The strategy in Hydroponic systems is to keep the system as clean as possible, by using pathogen-free growing material and by using disinfection and other sanitation techniques.

Even without a teaspoon of soil in your system, contamination of the soilless system can occur through the water supply, by air, insects or unknowingly by the grower or equipment.

In this section, we will discuss seven principles that will help you either reduce the initial population of the pest or decrease the rate of population growth of the pest. The cost of controlling a plant-pest population is relatively low when the pest population is low. Timely intervention is therefore very important.

Reduction of Population of Plant Pests

The initial population of a plant pest can be reduced through these four principles: exclusion, eradication, therapy, or verticle resistance.

1. Exclusion

These are measures applied directly against a plant pest to keep out pests from your growing environment. For example, planting seed that is certified to be free of weed seed, insects, and plant pathogens ensured the planter has excluded pests that are not established on the farm.

2. Eradication

This principle involves pest-control measures that get rid of pests already present in an area. Elimination of pathogens and insects in soilless media can be done through the use of the following chemicals:

• Sodium Hypochlorite- which is relatively inexpensive because of its widespread use.

• Hydrogen peroxide- is a strong oxidizing agent and can be used in the elimination of Fusarium, Pythium and viruses.

• Metham- sodium- Very effective against Fusarium and Pythium.

• Methyl bromide + chloropicrin- Effective against fungi, insects and nematodes.

3. Therapy

Therapeutic plant-pest control measures are those that control plant pests by acting directly against the pest and are made on the plant. Fungicides and insecticides are examples of therapeutic measures.

There is the problem of resistance of pathogenic fungi to fungicides, bacteria resistant to antibiotics and insect resistance to insecticides. These chemical interventions are designed to act specifically, and organisms can overcome this metabolic specificity.

It is therefore important to follow guidelines given by the manufacturer on use and have a variety of products that have different active ingredients.

4. Verticle Resistance

Verticle resistance is whereby a plant has the ability to stand up against a few strains of a pest population but is susceptible to the rest. Buying seeds that have been crossbred with resistant varieties is an example of verticle resistance.

One serious disadvantage of verticle resistance is it stands up only against wild-type strains of the pest and has no capacity to handle to new chemical-resistant strains of pest.

Decrease Rate of Growth

The remaining three principles of plant-pest control work by keeping pest populations in check during the cropping season. They include: Horizontal resistance, protection and avoidance.

1. Horizontal resistance

Horizontal resistance allows pests species only a fraction of what they need allowing the victimized plants to still thrive. This offers a stability to the plant which can survive the pressure of attack from different strains. As a manager of your hydroponic enterprise, it would be prudent to get the best variety to have the benefit of horizontal resistance.

2. Protection

In this principle, a barrier, either chemical or physical is placed on or immediately surrounding the plant to prevent pests in the vicinity from establishing pest-victim relations.

A common practice in hydroponic farming is the use of biological control agents that suppress root pathogens through parasitism, antibiosis, and competition of nutrients or space or induced resistance.

Biological agents of root-bourne (fungal) pathogens that have been made into products you can buy are Trichoderma harzianum, Gliocladium virens, G. cathenulatum, non-pathogenic F. oxysporum, Streptomyces griseoviridus, Coniothyrium minitans, and Bacillus subtilis.

3. Avoidance

Plant-pest control measures in which people work with the environment to enable their plants to escape contact with pest represents the principle of avoidance. This principle has been mentioned last but usually is the first to be considered before the use of chemicals.

Examples of avoidance measures include field sanitation, controlling ventilation, mulching and late planting. These examples clearly illustrate that the target of avoidance is the environment and not the pest or victimised plant.

Conclusion

In the 4000 year existence of Hydroponic farming, it has expanded into a vast sector in agriculture. Is it possible to answer all the fundamental questions on hydroponic farming in one article?

It is an impossible task, but what we have achieved is an understanding of the basics. Essentially what we have discussed includes:

• What is hydroponic farming

• Choice of hydroponic system and crop

• Nutrition and nutrient formulation

• Crop care

For more information and training check the following resources Latia Agribusiness Solutions or Hydroponics Africa.