Agriculture Column Tapuwa Mashangwa
THE use of hydroponics in Zimbabwe has the potential to revolutionise agricultural farming methods with regard to the technology and cost efficiency. Taking into consideration the unstable weather patterns we are experiencing it would yield better results.

Hydroponics is originally defined as crop growth in mineral nutrient solutions and it is a subset of soilless culture. Aeroponics is among the three main types of solution cultures in hydroponics, the others being static solution culture and continuous-flow solution culture.

It is a system wherein roots are continuously or discontinuously kept in an environment saturated with fine drops (a mist or aerosol) of nutrient solution. The method requires no substrate and entails growing plants with their roots suspended in a deep air or growth chamber with the roots periodically wetted with a fine mist of atomised nutrients.

Excellent aeration is the main advantage of aeroponics whose techniques have proven to be commercially successful for propagation, seed germination, seed potato production, tomato production, leaf crops, and micro-greens.

The limitation of hydroponics is the fact that 1kg of water can only hold 8mg of air, no matter whether aerators are utilised or not.

Another distinct advantage of aeroponics over hydroponics is that any species of plants can be grown in a true aeroponic system because the micro environment of an aeroponic can be finely controlled.

The limitation of hydroponics is that only certain species of plants can survive for so long in water before they become waterlogged. The advantage of aeroponics is that suspended aeroponic plants receive 100 percent of the available oxygen and carbon dioxide to the roots zone, stems, and leaves, thus accelerating biomass growth and reducing rooting times.

NASA research has shown that aeroponically grown plants have an 80 percent increase in dry weight biomass (essential minerals) compared to hydroponically grown plants; aeroponically grown plants requires ¼ the nutrient input compared to hydroponics and it uses 65 percent less water than hydroponics.

Unlike hydroponically grown plants, aeroponically grown plants will not suffer transplant shock when transplanted to soil, and offers growers the ability to reduce the spread of disease and pathogens.

Passive sub-irrigation, also known as passive hydroponics or semi-hydroponics, is a method wherein plants are grown in an inert porous medium that transports water and fertiliser to the roots by capillary action from a separate reservoir as necessary, reducing labour and providing a constant supply of water to the roots. In the simplest method, the pot sits in a shallow solution of fertiliser and water or on a capillary mat saturated with nutrient solution.

The various hydroponic media available, such as expanded clay and coconut husk, contain more air space than more traditional potting mixes, delivering increased oxygen to the roots, which is important in epiphytic plants such as orchids and bromeliads whose roots are exposed to the air in nature.

Additional advantages of passive hydroponics are the reduction of root rot and the additional ambient humidity provided through evaporations.

There is also Ebb and flow or flood and drain sub-irrigation.

In its simplest form, there is a tray above a reservoir of nutrient solution. Either the tray is filled with growing medium (clay granules being the most common) and planted directly or pots of medium stand in the tray.

At regular intervals, a simple timer causes a pump to fill the upper tray with nutrient solution, after which the solution drains back down into the reservoir.

This keeps the medium regularly flushed with nutrients and air. Once the upper tray fills past the drain stop, it begins recirculating the water until the timer turns the pump off, and the water in the upper tray drains back into the reservoirs.

In a run-to-waste system, nutrient and water solution is periodically applied to the medium surface. This may be done in its simplest form, by manually applying a nutrient-and-water solution one or more times per day in a container of inert growing media, such as rockwool, perlite, vermiculite, coco fibre, or sand.

In a slightly more complex system, it is automated with a delivery pump, a timer and irrigation tubing to deliver nutrient solution with a delivery frequency that is governed by the key parameters of plant size, plant growing stage, climate, substrate, and substrate conductivity, pH, and water content.

In a commercial setting, watering frequency is multi factorial and governed by computers or PLCs.

Commercial hydroponics production of large plants like tomatoes, cucumber, and peppers use one form or another of run-to-waste hydroponics.

In environmentally responsible uses, the nutrient rich waste is collected and processed through an on-site filtration system to be used many times, making the system very productive.

  • The writer is Engineer Tapuwa Justice Mashangwa, a young entrepreneur based in Bulawayo, Founder and CEO of Emerald Agribusiness Consultancy. He can be contacted on +263 739 096 418 and email: [email protected]

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