Irrigation management in greenhouse tomato production on rockwool

The many advantages of rockwool culture have led greenhouse vegetable growers to widely adopt the system. However, it has been difficult to harvest consistently high yields due to several factors such as, unsatisfactory spatial root development, rapid root collapse and random incidence of root diseases. Improved water management could alleviate some of these problems, thereby improving greenhouse vegetable yield and quality. The present study tested six irrigation management strategies on the productivity of rockwool grown tomatoes (cv. Rapsodie) in 2004. Four of the treatments, based on the use of an electronic water content meter (WCM) delivered irrigations when the slab water content (SWC) was <= 60, 70, 80, or 90% while the other two treatments, based on the use of a crop balance, applied irrigations after a 700 or 500 g loss in the daily-adjusted slab weight (LDASW). Initially, we noticed a heterogeneous EC build-up in the slabs across various treatments, which distorted the expression of treatment effects on plant growth, yield, and water use. To minimize this problem, an EC control strategy of applying extra irrigation was devised and adopted in two sequential phases,; 1) application of a 30 min long extra irrigation twice a week (for 7 weeks) and 2) extra irrigation(s) when the slab EC was >= 3.5 mS/cm (for 5 weeks). Slab EC was well controlled in both these phases and we observed significant improvements in root growth and marketable yield. We concluded that irrigating at 70-80% SWC was best for maximum root growth as well as for marketable yield. The two irrigation treatments based on the 700 and 500 g LDASW performed equally well producing marketable yields comparable to those produced by irrigating at 70 or 80% SWC.