Sustainable Cultivation Approaches

for the Improvement of Soilless Tomato Production

in the Mediterranean Environment

The most common approach for soilless cultivation in the Mediterranean area is represented by free-drain (also called “open-cycle”) cultivation (nutrient solution is supplied in excess, and the leaching fraction is released into the environment, resulting in excessive water and fertilizers consumption and huge amounts of fertilizers released into the environment). When no good quality water is used for irrigation (as in the case of moderate saline water use) and the irrigation management is conducted empirically, the leaching rate can reach 30-50% of the total nutrient solution supply. This cultivation approach compromises the overall sustainability of soilless cultivation.

Closed cycle nutrient solution recirculation is considered the preferred approach to be adopted in order to boost the sustainability of soilless cultivation. However, in the Mediterranean environment, characterized by low-tech greenhouses, closed-cycle is still poorly adopted. In addition, when saline water is used, as commonly occurs in the Mediterranean areas, continuous recirculation is difficult to be applied, while semi-closed cycles are more commonly adopted (periodic renewal of recirculating nutrient solution and discharge into the environment of exhausted solutions).

Increasing interest is currently reserved for the use of sensors for the measurement of substrate parameters (moisture, electrical conductivity, temperature), integrated in smart systems for the automatic irrigation and fertilization management.

During August-December 2020, we produced tomato fruits in a greenhouse using soilless cultivation. Plants were grown in perlite, a largely used soilless substrate. Three different cultivation approaches were adopted: free-drain with empiric management of the irrigation and fertilization; semi-closed cultivation (renewal of the recirculating nutrient solution when a 5 dS/m was exceeded); smart irrigation (a wireless sensor network was used to monitor substrate moisture variations and salts accumulation trend in the substrate: an automatic system controlled water and fertilizers supply based on rela plant needs and leaching was applied only when substrate EC exceeded a threshold value of 5 dS/m).

Both semi-closed cycle and sensor-based smart irrigation management reduced the environmental impact of the production process by lowering water/fertilizers usage and the nutrient solution released into the environment. The smart approach was also able to substantially increase the water use efficiency. The application to apply controlled osmotic stress (corresponding to a 5 dS/m threshold value) positively affected tomato quality traits.