Drip irrigation emitter clogging in Dutch greenhouses as affected by methane and organic acids

It is believed that the serious clogging of drip irrigation emitters in the Dutch greenhouse industry is caused by methane-oxidising bacteria and/or organic acids used as anti-clogging agents. In this study greenhouses with moderate to severe emitter clogging have been examined. High methane concentrations—up to 69 mg/l—were found both in ground water (GW) and in the water from reverse osmosis (RO); however, in the fertiliser-mixing tanks (MTs), methane concentrations were <0.01 to 9 mg/l. In trials, a methane concentration of 0.11 mg/l in the fertiliser-mixing tank (MT), giving 0.08 mg/l at the emitter outlet, caused severe clogging of tube emitters and after prolonged exposure, also of labyrinth emitters. Slime in the emitter with ‘methane treatment’ contaminated not only higher carbon and adenosine triphosphate, but also higher element concentrations than in the non-methane treatment. Biofouling increased the deposits of salts (scaling). To avoid emitter clogging, growers using ground water should carefully volatise the methane gas if it is present in the fertiliser-mixing tanks at concentrations higher than 0.01 mg/l, i.e. the detection limit. Organic acids, i.e. acetic acid and formic acid, were shown to increase the growth of Trichoderma, a fungus often isolated from emitter slime. Commercial anti-clogging agents containing organic acids were not effective in killing Trichoderma. It is likely that the carbon of the acids serve as a substrate for the micro-organisms. The use of anti-clogging agents without organic acids is advisable.