During an interview which took place last 21 November on the platform tacler, Professor Antonio Elia from University of Foggia (Italy) explained the work of his research group within the EU project Quafety. Especially, scientists have investigated the different soilless cultivation systems to produce leafy vegetables for fresh-cut industry.

The soilless systems allow the growth of plant without soil: the roots are in the nutrient solution (water plus nutrients) with or without substrate (not soil) for mechanical sustain. Professor Elia (in the photo) said: "There are different classification schemes for soilless cultivation systems. In general it is possible to summarize them in: 'liquid' and 'substrate' systems. The 'liquid systems' include the Nutrient Film Technique (NFT) and Ebb and Flow System (dynamic system, with recirculating water) and Floating System (static system). The 'substrate systems' include as growing media: a) inorganic natural materials (gravel, rockwool, glasswool, perlite, vermiculite pumice, zeolite etc); b) inorganic synthetic materials (foam-polyurethane, oasis-plastic foam, etc); c) organic material (bark, peat, wood chips, etc)."

Several research works have been published on the advantages of soilless cultivation. The soilless technique gives the possibility to use unsuitable soils (high salinity, toxic substances, accumulation of soil pathogens), to eliminate the soil sterilization need, to reduce the labour requirement for soil preparation and management, to control the root environment in terms of temperature and oxygen, to reduce or eliminate the pathogenic attacks to the root system, to save water and nutrients, to increase the yield, to optimize plant nutrition, to reach a greater uniformity and precocity of yield, to reduce or to overcome the need for chemical applications in the control of soil pathogen diseases or weeds, to increase the degree of labour automation.

Within Quafety, the research group led by Professor Antonio Elia is focusing on the definition of innovative protocols for the management of soilless systems, that are actually considered the most intensive production method in today's horticulture industry. Especially, the scientist have worked on model species, such as rocket salad, endive, escarole, lettuce. The main objectives are:

• to define an easy soilless system for growing leafy vegetables;
• to decrease nitrate accumulation in leaves;
• to obtain a product safe grown with high hygienic conditions that has a very low microbial load;
• to obtain a product suitable for fresh-cut industry.

The specific activities of the work are:

improving fresh cut safety: soilless systems are based on the reduced use or the complete absence of agrochemicals in the growing process, which can result in products less contaminated and at the same time with a lower microbial load, without losses in quality compared to soil cultivation. Two soilless techniques have been considered (Ebb and Flow system vs. Floating system);

improving nutritional quality: soilless systems allow a direct control of plant nutrients supply. Nutrient solutions may be modified during the cycle in order to control the quality of the product. Examples of these strategies are products with near-zero nitrate content using nutrient solution deprived of N in the last part of the cycle, or products with high content of dry matter and antioxidants using nutrient solution with high level of electrical conductivity, when it is possible to increase it;

selecting the most suitable cultivars for fresh cut production: mainly taking into account, dry matter, natural antioxidants and nitrate content;

improving the shelf-life of the product: increasing the EC of nutrient solution it is supposed to a) improve the content non-phenolic antioxidants which would contrast browning phenomena; b) increase the content of dry matter though the management of nutrient solution.

Professor Elia explained: "The difference between Ebb-and-Flow and Floating system is represented by the distribution of nutrient solution. In the Floating System the trays float on the nutrient solution, while in Ebb and Flow System the trays are sub-irrigated discontinuously by a time-dependent nutrient solution supply. Therefore, for the Floating System, being a static soilless system, oxygen level for roots could be problematic, differently, in the Ebb and Flow System the periodic movement of nutrient solution at the bottom of benches allows a better oxygen enrichment within the growing substrate".

"The two soilless systems are rather similar, but Ebb and Flow was selected with the aim to reduce the inputs of water and nutrients. Moreover, since Ebb and Flow System determines a light water stress compared with Floating System, it is expected the Ebb and Flow System gives a product more suitable for fresh-cut processing. Ebb and Flow System has also the advantage to have no problem in oxygen delivery to the roots, providing a better growth in some species under consideration very sensible to the depletion of oxygen in the rooting media."

Results of the experimentation showed that the response of the all tested species (rocket salad, endive, escarole, lollo and romaine lettuce) to salinity level (EC - electrical conductivity: EC1 ≈1.5 dS/m; EC2 ≈2.5 dS/m; EC3 ≈3.5 dS/m EC4 ≈4.5 dS/m) of nutrient solution is in favour to the intermediate level. The EC3 (≈3.5 dS/m) gives both a good yield and a product suitable for fresh-cut processing in terms of physic (high level of dry matter accumulation, low weight loss during the cold-storage) and nutritional/safety parameters (low accumulation of nitrates). The replacement of nutrient solution with water 3 day before harvest determines the reduction of nitrate in all tested species up to 75%, without negatively affecting yield. It is not recommended to apply this strategy for a longer time, for the negative effect on yield.

The Ebb and Flow System (EF) does not yield differently from Floating System (FS), moreover it allows a product more suitable to fresh-cut processing compared to FS. The EF product shows a higher dry matter content, a lower level of nitrates, and a weight loss similar during the storage compared with the FS product. Beyond these positive peculiarities of the raw material, the EF requires a lower input of water and minerals. The nutrient solution management in EF must be scheduled on a number of nutrient supplies not lower than 3/day.

The full version of the interview is available at www.tacler.com in quafety section.