2017 ASHS Annual Conference

Biofilm, bacteria enclosed in a polysaccharide matrix, accumulates on the inner surface of irrigation pipes resulting in clogged emitters. The objective of this project was to measure if biofilm buildup differed when a nutrient solution was applied at different irrigation frequencies and pipe materials. Pond water was treated with a complete fertilizer applied at 200 mg per L of nitrogen. The three irrigation frequencies tested were 30 s every 10 min, 2 min twice a day, and continuous flow. The two pipe materials tested were polyethylene (PE) and polyvinyl chloride (PVC). The materials and irrigation frequencies were chose based on common greenhouse practices. The experiment was conducted for four weeks and was repeated twice. The experimental design was a full factorial completely randomized design with six replicates per treatment and the experiment. Biofilm was measured in terms of total biomass and aerobic and viable bacteria attached to the inside surface of the pipe. Aerobic planktonic bacteria and water quality were also measured. All measurements were collected on week 4. Total biomass and attached bacteria were highest on PVC irrigated at a frequency of 30 s every 10 min, both measurements were higher by one or two orders of magnitude compared with the treatments combinations. Total biomass and attached bacteria was overall higher in PVC compared with polyethylene. No differences were observed in planktonic bacteria. The results of this project suggest that growers using a higher frequency of irrigation (e.g. greenhouse propagation mist houses) would benefit by using polyethylene tubing.