Electrical Conductivity of Nutrient Solution, Plant Growth and Fruit Quality of Soilless Grown Tomato

Tomato plants (cv. Naomi) were grown until the 8 cluster in a greenhouse during Aug. 1998 – Jan. 1999 using a closed sub-irrigated soilless system. Plants were raised in pots (10 L) filled with peat and pomice (1:2 v:v) substrate. Forty days after transplanting 3 nutrient solutions (NS) with electrical conductivity (EC) of 2, 4, and 6 dS/m were applied to the plants. The ECs were achieved by preparing NSs from rain water (low EC) or from well water (high EC). Intermediate EC was obtained by mixing equal parts of the 2 and 6 dS/m NS. Seventy days from the beginning of treatments stem length, number of leaves, fresh and dry weight of stems, leaves and fruits, leaf area and number of fruits were recorded. The substrate was separated in two layers of equal depth, and tested for pH and EC. Qualitative analyses were performed on ripe fruits. By increasing EC of NS from 2 to 6 dS/m the fresh weight of leaves, stems, and fruits decreased linearly. No influence of salinity was observed on dry weight or stem elongation (on average 233 cm). By increasing EC of NS the mean weight of fruits decreased while titratable acidity, soluble solids, ascorbic acid, vitamin C and sugar contents of fruits increased. With the increasing EC of NS from 2 to 6 dS/m, both pH and EC in the aqueous extract of the deeper substrate layer rose from 6.5 to 6.7 and from 1.1 to 2.8 dS/m, respectively, while in the upper layer pH decreased from 6.8 to 6.6 and EC increased from 3.9 to 8.8 dS/m, in all cases following a linear pattern.