Sub-irrigation methods for growing potatoes in containers under a rainshelter

Potatoes were grown in a polyethylene-covered rain shelter at an 850 in elevation in Hawaii. Nutrient solution (1.5 mS) depths of 2.5 to 5 cm were maintained in growing tanks (3.7 in long x 0.6 m wide) by gravity flow to float valves. Two 'Catalina' potato tubers were planted in bottom-perforated polyethylene bags supported by the tank floor and 3 tubers were planted in nursery trays (17x17x5 cm) elevated 5 cm above the tank floor. The bags and trays contained 2 litres of growing medium per potato seed tuber and these containers were subsequently 'hilled' 3 times with dry grass. Total sellable yields of potatoes growing in nursery trays, 11.4 and 18.9-litre bags were 5.4, 4.6 and 5.1 kg/m(2) (based upon tank area), respectively. In another experiment, no significant yield differences were observed from 'All Blue' and 'Catalina' potatoes which were grown similarly in 18.9-litre bags, in 10-cm slit-sided pots supported by a 2.5-cm-thick expanded polystyrene top-cover for the tank, and when potato seed tubers were wrapped in newspaper which rested on 5-cm-high nursery tray. All 3 treatments were hilled with dry grass. Bottom-perforated 8-litre pots containing upside-down 3-litre pots were filled with 5 litres of 3 growing media and these pots were sub-irrigated. Total sellable yields of 'All Blue' potatoes in peat-perlite, salty clay loam soil or decayed 2 wood chips were 4.9, 2.1 and 5.4 kg/m, respectively. There was no yield advantage from planting 6 'Catalina' seed potatoes per bag as compared to 2 potatoes/bag. However, sellable potato yields from bags planted with 4, 20 and 52 g (+/- 15%) seed 2 tubers were 5.2, 6.5 and 7.5 kg/m(2) respectively.