Our ancestors have a saying: All things are born from the earth! Before we talk about today’s topic, let’s do some divergent thinking first: Which plants on earth do not grow in the soil? In the past, people might need some time to answer this question, but now, when facing this question, many may blurt out: All plants can grow without soil! Yes, this is exactly what we are going to talk about today – soilless cultivation!
I. What is soilless cultivation?
Soilless cultivation is a method of growing plants without the use of natural soil. The roots of plants grown with soilless cultivation are separated from the soil environment, and rely entirely on artificial provision of nutrients and water to meet their growth needs. First, let’s understand the necessary conditions for plant growth:
Sunlight: Photosynthesis is essential;
Air: O2, CO2, etc.;
Water: Essential for life activities;
Nutrients: Mainly mineral elements from the soil.
The role of soil is merely to provide an environmental space for root development, and supply plants with the required nutrients and water. However, research has found that given suitable climatic conditions, mainly satisfying the conditions of water, air and nutrition, plants can survive and grow even without soil.
II. Major modes of modern soilless cultivation
Hydroponics: (including NFT, DFT and FCH)
(1) Nutrient Film Technique (NFT): The nutrient solution in the planting tank is maintained at a depth of about 0.5 cm with circulating flow. The roots of plants are placed in the shallow flowing nutrient solution to absorb water and nutrients.
Advantages: Fast flow of nutrient solution ensures sufficient oxygen to the root zone, and uniform distribution of nutrients. Simple planting tanks, low cost, high degree of automation.
Disadvantages: Pumps need to run for a long time, consuming more electricity. Also, in case of power failure, the nutrient solution will stop flowing quickly.
(2) Deep Flow Technique (DFT): The nutrient solution in the planting tank is maintained at a depth of more than 2 cm. The root masses of plants extend into the nutrient solution to absorb water and nutrients. Water pumps drive the circulation and oxygenation of the nutrient solution, or air pumps or oxygen generators can be used to supplement oxygen.
Advantages: Intermittent operation of water pumps for aeration saves electricity. In case of power failure, it will not cause oxygen deficiency in the water in a short time.
Disadvantages: The construction investment of planting tanks is relatively large. Improper operation often leads to oxygen deficiency in the roots.
(3) Floating Board Capillary Hydroponics (FCH): An improvement of DFT, with a similar device. The difference is that a foam board is added on the nutrient solution in the planting tank, covered with a layer of non-woven fabric to increase air exchange around the roots.
The non-woven fabric absorbs the nutrient solution from the tank. The roots grow on the saturated non-woven fabric. One part of the roots extends into the nutrient solution to become “solution roots”, and the other part forms “humidity roots”.
Advantages: Better air exchange in nutrient solutions, more electricity saving, and longer tolerance for power outages.
Substrate drip irrigation: Refers to soilless cultivation by using non-soil solid substrates as carriers for plant roots, and precisely supplying nutrient solutions to the root zone of plants in a timed and quantified manner. Cultivation methods with different substrate carrying approaches:
Rock wool cultivation: Use agricultural rock wool blocks as substrate placed neatly, and directly transplant (or sow) plants into the rock wool.
Bag cultivation: Put substrates into bags, open planting holes in the bags, and transplant seedlings into them.
Tank cultivation: Make planting tanks with solid materials, put substrates in the tanks, and directly transplant seedlings into the substrates.
Performance requirements of soilless cultivation substrates:
(1) Suitable for growing various types of plants at all growth stages.
(2) Low bulk density, high total porosity, great water absorption, and strong water holding capacity. Good air permeability.
(3) Certain elasticity and extensibility. Does not crack when too dry, does not clump when too wet.
(4) Good heat insulation properties, no deformation or deterioration due to high temperatures, fumigation, freezing, etc.
(5) Chemically inert, no chemical reactions with fertilizers and pesticides.
(6) No foul odors, does not pollute soil.
(7) Easy daily management, not too expensive.
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