EFFECTS OF INCREASING THE SALINITY OF THE NUTRIENT SOLUTION WITH MAJOR NUTRIENTS OR SODIUM-CHLORIDE ON THE YIELD, QUALITY AND COMPOSITION OF TOMATOES GROWN IN ROCKWOOL

Tomato plants grown in rockwool at a salinity of 3 mS cm-1 were compared with those at 8 and 12 mS cm-1, where the higher salinities were achieved by addition of either major nutrients (NO3-N, K and Ca) or NaCl. Increasing the salinity progressively reduced the yield of fruit (fresh weight) but increased the proportion graded as high quality (Class 1). Similar responses to both sources of salinity were obtained at 8 mS cm-1. The number of fruit produced, the dry weight per fruit and their reducing sugar content (g per fruit) were decreased at 12 mS cm-1. Added major nutrients affected vegetative growth adversely at 12 mS cm-1, and reduced the size, dry weight and sugar content of the fruit as compared with NaCl. At both 8 and 12 mS cm-1, the acidity of the fruit juices was higher with added major nutrients than with NaCl, as was the total acid content per fruit. Whilst the data are consistent with a specific role of K in controlling fruit acidity, they show that much of the increased acidity of the fruit juices is related to the reduced water content of the fruit, i.e. to the salinity, rather than to the applied K level per se.