Acidification of Water Used in Glasshouses

The pH of water used for irrigating and feeding tomatoes in glasshouses should be lowered to 5.5-6.0 in order to reduce the incidence of blocked trickle-irrigation nozzles and to prevent a high pH developing in the growing medium as the season progresses. This pH range is also suitable for nutrient solutions used in nutrient-film and rockwool growing systems. Results of acidification tests showed that 68, 205 and 268nml of 72% HNO3 were sufficient to reduce the pH of 1000l of water to 6.0 in three samples with initial pH values of 7.30, 7.35 and 8.30. respectively. This shows that acid must be added carefully by the grower as relatively small amounts have a large effect on the pH of the water. The pH of acidified water samples rose only slightly up to 48h after acidification, but after 6 days the increase was more considerable. This suggests that the target pH should be reduced by 0.5 of a pH unit to allow for this change.