THE EFFECT OF INTERMITTENT IRRIGATION WITH COLD NUTRIENT SOLUTION ON THE GROWTH OF TOMATO SEEDLINGS PROPAGATED IN ROCKWOOL

Seedlings of tomato, cv. Counter, propagated in rockwool blocks were irrigated five times every 24 h with nutrient solution at 10-degrees-C or 18-degrees-C for up to three weeks. The mean block temperature was lowered by 3.5-4.0 degrees C by irrigation at 10-degrees-C. One week of irrigation at the lower temperature caused the seedlings to develop a characteristic dark purplish colour. This treatment reduced fresh weight and leaf area but not dry weight which suggests that water uptake was also reduced. Dry weight was reduced following two or more weeks of irrigation at 10-degrees-C. When seedlings which had been irrigated at 10-degrees-C were returned to irrigation at 18-degrees-C, the purple colour slowly disappeared and the percent dry matter decreased. When plants were grown on, the total yield of fruit was unaffected by these seedling treatments.