NITROGEN AND AERATION LEVELS OF THE NUTRIENT SOLUTION IN SOILLESS CULTIVATION SYSTEMS AS IMPORTANT GROWING CONDITIONS AFFECTING INHERENT QUALITY OF BABY LEAF VEGETABLES: A REVIEW

The floating system (FS) is an easy and profitable growing technique for the cultivation of baby leaf vegetables (BLV), since plants can be grown at high densities, giving high yields in short time and clean commercial products. Use of FS allows for influencing nutritional status and composition of plants modifying the nutrient solution (NS), particularly the final nitrate and oxalate contents, one important aspect in BLV. As in other hydroponic systems, plants grown in FS may suffer hypoxia because the roots gradually consume the oxygen dissolved in the NS. This work reviews the effect of the nitrogen concentration and chemical form supplied to the growing plants and the aeration level of the NS on the inherent quality of BLV. Studied species included rocket (Eruca sativa; Diplotaxis tenuifolia), lamb’s lettuce (Valerianella olitoria), water and garden cress (Nasturtium officinalis; Lepidium sativum), lettuce (Lactuca sativa), purslane (Portulaca oleracea), spinach (Spinaca oleracea) and bladder campion (Silene vulgaris). For many species, concentrations from 4 to 16 mmol L-1 N were used in the NS and ratios between N-NO3- and N-NH4+ from 100 to 0% were applied. In general, 8-12 mmol L-1 N led to high yields and limited leaf NO3 accumulation and 40-60% of N-NH4+ limited leaf NO3 accumulation. With respect to the aeration levels of the NS, some species showed little sensitivity to oxygen depleted in the root medium, and were able to adapt to a gradual reduction in oxygen level. However, to increase yields, aeration is advisable, although the final quality of the product, in terms of functional phytochemicals concentrations, may be slightly lower. The level of oxygen had a different influence on the oxalate and nitrate contents depending on the studied species.