ISHS International Symposium on Growing Media and Hydroponics WAYS OF REDUCING ROCKET SALAD NITRATE CONTENT

Summary To determine the influence of potassium levels in the nutrient solution on lycopene content, tomato plants were grown in a soil-less system using rockwool slabs as substrate. Two growing seasons were studied with the aim of comparing three potassium levels: low, medium and high (corresponding to 150, 300 and 450 mg K l^–1 in the nutrient solution). In the first growing season (Spring–Summer), two high-pigment cultivars of tomato (Solanum lycopersicum L.,‘SVR’ and ‘Kabiria’) were compared. In the second growing season (Summer–Winter) ‘Esperanza’, a non high-pigment hybrid and the two previous cultivars were used. Total fruit yield was higher in the Summer–Winter growing season than in the Spring–Summer season, but was not influenced by potassium nutrition. Growing season, potassium level, and the genetic traits of the cultivars influenced the principal quality parameters of fruit, with higher dry matter and total soluble solids contents in the first growing season, correlating with lower lycopene and K⁺ contents in the fruit. The lycopene content increased linearly with increasing potassium level in the nutrient solution. The high-pigment genotypes showed a higher lycopene content than ‘Esperanza’. The higher lycopene content in ‘Kabiria’ fruit can also be related to the size of the fruit.

The aim of this research was to compare the cultivation of tomato (Solanum lycopersicum L.) plants in soil with two hydroponic systems: the Nutrient Film Technique (NFT; closed cycle), and rockwool (open cycle), in terms of yield and water-use efficiency (WUE). Two trials were carried out, one in Winter-Spring (WS), and the other in Autumn-Winter (AW). In both trials, four tomato cultivars were used: two of the beefsteak fruit-type (‘Diana F1’ and ‘Jama F₁’), and two of the cherry fruit-type (‘Naomi F₁’ and ‘Conchita F₁’). The two hydroponic systems showed greater earliness; on average, 10 d and 8 d earlier than in soil, in the WS and AW trials, respectively. Total fruit yield was influenced by the growing system. In the hydroponic systems, total yields were 11% and 7% higher in the WS and AW trials, respectively, than in the soil system. Cultivation in soil gave good results in terms of WUE in both trials, due to the use of tensiometers, suitable watering volumes, and mulching. Between the two hydroponic systems, NFT gave a higher yield, with lower water and fertiliser use, and a greatly reduced environmental impact.