SOIL-LESS CULTIVATION

Soil-less cultivations, or "hydroponic" cultivations as they are better known, consist in the cultivation of plants without the help of soil, broadly speaking.
Cultivation takes place in the same environments, mainly in greenhouses, where plants are cultivated in substrates, cultivation trays or flood benches placed on the ground through a very careful management of the nutrient solution (water + minerals).

The reasons for choosing soil-less cultivation are numerous, however the main reason usually has to do with the possibility of avoiding and/or limiting some pathologies of the roots and the effects of soil fatigue.
The main soil-less cultivation systems can be divided into two groups:

• a) open cycle (disposable nutrient solution)
  
  
• b) closed cycle (recirculating nutrient solution).
  

The most-used system is a substrate open cycle system that foresees the use of substrates that are sold in bags and/or different-sized vases.
The substrates can be organic (peat, marc or algae), inorganic (rock wool, perlite, pumice) and sometimes mixes of both. The nutrient solution is distributed to the plants through a drop irrigation system that doesn't foresee the recovery and recirculation of the excess solution. However, the system can easily be transformed into a closed cycle system.
The most important closed cycle systems are: NFT; aeroponic and floating system.

The first Nutrient Film Technique represents hydroponics in the strict sense of the word, in that the cultivation develops the roots in plastic trays that can be of different sizes. At preset times, the nutrient solution flows through these trays, is then cleaned and recirculated.

In the aeroponic system, the plants are placed on panels, which are usually in plastic or Styrofoam, where the nutrient solution is nebulized on the roots.

The third system consists of cultivation tubs that contain the nutrient solution on which perforated Styrofoam panels with plants float (usually for leafy cultivations).

The fundamental elements that should be taken into consideration when projecting and deciding the size of a soil-less cultivation facility are:

• cultivation environment (temperature, RH, lighting, wind factor, evapotranspiration)
  
• the quality of the water
  
• species and varieties of crops
  
• mixing and distribution system of the nutrient solution
  
• substrate/system.
  
  

The micro-climate in the protected environment and the management of the parameters that determine this environment have a strong influence on the choices regarding the cultivation system (type of substrate, characteristics and volume of substrate, hourly flow-rate of the drippers, etc.). The evapotranspiration and the volume of water available in the substrate should be connected with the quality of the water available, keeping in mind the specific needs of the species.
The main characteristics of the water that should be considered are: chemical (macro- and micro-elements, pH, EC) and physical and biological (temperature, presence of micro-organisms, etc.).

An excess of certain chemical elements in the water can be harmful for some species, and sometimes can be a limit for certain systems (recirculation) and/or certain substrates (low water retention, low padding).

Once the analysis of the water, corrected with the help of fertilizer salts and acids or bases, is known, concentrate solutions are created to optimize stock and distribution. Normally, at least two concentrate solutions are created so as to keep non-compatible salts ( for example, calcium salt >< phosphate salt) separate. These solutions are then diluted on the basis of the preset EC and pH parameters. The dilution is implemented with different systems (volumetric dosing, dosing pumps, computer), that are more or less sophisticated, that mix the water using different methods (volumetric, pH and EC feedback, in-line injection, open tank). The composition of the nutrient solution depends fundamentally on the parameters mentioned above (climate, substrate, water quality) and obviously on the species and varieties of the crops. Often the characteristics of the varieties are crucial because they can be quite variable within the same species, therefore knowing certain parameters, like vigour, earliness, type of hypogeous and epigeous structures, EC tolerance, considerably help the correct management and formulation of the nutrient solutions.

To be continued ...

Simonetti Adamo
Tel +39-0438-900114 Fax +39-0438-900168
e-mail: simonettiplast@tin.it

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