Plants need soil for two main reasons: firstly for anchorage, that is, providing physical support to the crop by holding its roots firm and, second, to access nutrients that are in the soil for nourishment.
But you can still produce healthy crops without using soil. Soilless crop production involves finding alternative ways to provide the anchorage and access to nutrients at the right time.
Therefore, soil can be done away with once a farmer figures out how to anchor the crop and provide nutrients.
Soilless gardening differs depending on the type of growth media used.
You can choose to use an inert growth media, which is in form of solids like sand, coco peat, gravel, rock wool vermiculite, haydite, clay pebbles, vydron and perlite.
The growth medium can also be a solution, where the plants are grown in water that is mixed proportionally with the requisite plant nutrients.
These nutrients are both macro (needed in large quantities) and micro (those only needed in smaller amounts).
Plants can also be suspended in the air, such that the roots hang and nutrients are mixed with water and aerosolled, after which they are sprayed to the roots at predetermined intervals for nourishment of the crops. This type of soilless crop production is known as aeroponics.
Macro-nutrients needed by plants in their lifetime include potassium, phosphorus, nitrogen, magnesium and calcium.
They are five in number, while micro–nutrients are seven, namely zinc, iron, copper, manganese, borate, sulphur and molybdenum.
These minerals should be available with a favourable pH range, which affects the level of availability of some nutrient elements like phosphorus (P), which is normally unavailable at extreme ranges.
The ideal pH level is between 5.8 and 6.7, with an electric conductivity range of 1.4 to 2.6.
TECHNIQUES OF SOILLESS GARDENING
There are six known soilless techniques that have stood the test of time. These are deep water culture, nutrient film technique, ebb and flow, drip system, aeroponics and wicking system.
Deep water culture involves the use of styrofoam, which holds the plants as their roots float in a treated solution, mixed with nutrients that are taken up to nourish the plants. Air is pumped into the solution or substrate to supply oxygen.
This system is suitable in production of leafy vegetables like lettuce and spinach, which don’t produce much roots.
Ebb and flow involves the use of growth trays where a growing media is held. The growth medium in this case is solid, the case of sand, gravel, rock wool or any other deemed suitable by the farmer.
Nutrients are supplied to the plants in a solution form (nutrients diluted in water). In this technique, the media is first flooded with nutrient solution using a submerged pump and timer, with the excess solution draining back to the reservoir.
The technique also needs an acidity/alkalinity monitor as well as an electric conductivity monitor to regulate the conditions of growth.
In the drip system, nutrient solution is released at the base of each plant inside the media.
It is in two forms, the first one being recovery drip system, where after the solution has been released to the plants, the excess in the media is drained back to the tank and is reused.
The second type is non–recovery drip system, where once nutrient solution is released to the media, it’s used up.
Drip system uses coco coir, rock wool or peat moss due to their high–water retention ability.
Nutrient film technique is the most used type of soilless crop production due to its many benefits. It does not need a timer under the water pump.
The nutrients are supplied in the trays over the plant roots, while excess drains into the reservoir.
This technique only uses water as the growing media while plants are supported by small plastic baskets as the roots dangle into the nutrient solution.
Aeroponics is the most technical system that uses air as the growth medium. The plants’ roots hang in the air and are misted by nutrients from time to time in a short interval of 5-10 minutes.
Its requirements include a reservoir pump and spray nozzles, growth media nutrient solutions, pH and totally dissolved solids (TDS) controller, which is basically an electric conductivity meter that displays readings in parts per million (ppm).
Wicking system is the simplest soilless growing system.
Nutrients are released into the growth tray through a wick. One needs a growth tray, growth media, nutrient solution, air pump and diffuse, pH and EC/TDS testers.
Soilless gardening is profitable if done well since the crops mature early, ensuring all-year-round production.
Oduor is based at the Department of Crops, Horticulture and Soils, Egerton University
