USE OF HIGH ELECTRICAL-CONDUCTIVITY OF NUTRIENT SOLUTION TO IMPROVE THE QUALITY OF SALAD TOMATOES (LYCOPERSICON-ESCULENTUM) GROWN IN HYDROPONIC CULTURE

Summary. The effect of the electrical conductivity (EC) of nutrient solution on total soluble solids (TSS) and fruit yield was studied, using table tomatoes grown outdoors in hydroponic culture, with the aim of seeing if salt stress could be used to increase TSS and thereby improve fruit quality. Two initial experiments compared the responses of 3 different cultivars and compared responses to different salts. The main experiment aimed to quantify the trade-off between yield and TSS as EC was raised with NaCl. In the main experiment, TSS of cv. Flora Dade increased linearly from 4.40 to 5.94-degrees-Brix over an EC range of 1.5-9.0 mS/cm. Over all 3 experiments, the mean TSS of Flora Dade increased by 0.16-degrees-Brix/mS.cm rise in EC above the control EC of 1.5-2.0 mS/cm. The 3 cultivars responded similarly to raised EC, although they ranged in TSS from 4.1 to 5.4-degrees-Brix under non-saline conditions. Raising solution EC with NaCl, KCl, or a mixture of NaCl/CaCl2 all gave significant increases in TSS. Increasing EC also increased titratable acidity and reduced fruit size, but had no effect on fruit firmness. Yield in the main experiment declined with increasing EC, but not linearly. Over all experiments, it was shown that salt stress could be used to achieve an increase in TSS of about 0.5-degrees-Brix with little or no effect on yield. However, the EC at which this increase occurred appeared to depend on weather conditions.