To better understand the dynamics behind these systems, we talked to Francesco Giuffrida, Professor of Horticulture and Floriculture at the Department of Agriculture, Food and Environment at the University of Catania.
Professor Francesco Giuffrida
Proper management leads to higher yields
"If managed properly, soil-less cultivation techniques can lead to higher yields and a better quality while needing less water and minerals. Of course, only a limited quantity of substrate is available for these crops: for example, plants can use a volume up to 150 litres in normal crops while they can only use 6 in soil-less crops. This corresponds to 12 and 2 litres of water per plant for sandy soil and organic substrates respectively."
"But organic substrates could pose a few problems compared to inorganic ones, such as the fact that they are more difficult to reuse over the years and their chemical inertness itself, as it makes it more difficult to monitor nutritional solutions in contact with the roots. However, organic substrates can be more easily disposed of, as they can be considered a by-product."
Choosing a substrate is often linked to economic aspects (purchase cost, annual cost, etc.) rather than to its physical and chemical characteristics, which become however essential when the correct irrigation volume must be calculated.
"The volume of water retained by a substrate - which can be estimated empirically or measured with a precise analysis - and drainage percentage are essential to assess the quantity of water needed for each irrigation operation. There is no fixed value when it comes to drainage percentage, as it depends on the conductivity of the nutrient solution and on crop tolerance to salinity and therefore its response in terms of quantity and quality. In addition, the conductivity of the solution coming into contact with roots does not correspond to that of what was drained."
The methods to objectively define irrigation frequency are based on the measurement (volume sensors)/ estimate (mathematical models such as Penman-Monteith) of substrate humidity or on the measurement (scales) of the water used by the crops. Applying these methods requires a certain level of technical knowledge and adaptation to different application conditions.
Another example of soil-less crops
Creating nutrient solutions
One last aspect to consider is the composition of nutrient solutions as formulations are often created in environments (central-northern Europe) that have a different climate compared to the Mediterranean.
"In our conditions, the quantity of nutrients absorbed by plants per volume unit of water can be significantly lower than in central-northern Europe. A less-concentrated solution would help reduce problems due to bad-quality water and the release of large quantities of mineral elements into the soil. Finally, considering the high competitiveness of the sector and the public level of awareness for environmental problems and harmful substances in food, turning to soil-less cultivation techniques could be an interesting opportunity."