Wednesday, 28 August 2013 12:14

QUEBEC, CANADA—The same nutrients plants need to grow can be detrimental in the wrong concentrations. When greenhouses recycle their irrigation water by collecting effluent water and recycling it for use on growing plants, there is a risk of exposing plants to unsafe accumulations of nutrients and pathogens.

That's where artificial wetlands come in. "The use of artificial wetlands for greenhouse wastewater treatment could be an alternative way to reduce the environmental burdens associated with nutrient leaching and consequently to increase the sustainability of greenhouse production systems," said Nicolas Gruyer of Quebec's Universite Laval. Gruyer and colleagues authored a study published in HortTechnology that investigated the ability of artificial wetlands water to successfully irrigate and suppress pathogen growth in tomato plants.

The research team created an artificial wetland by planting cattail plants 14 months before the experiment and exposing the plants to one of three treatments. For the first treatment, the wetland area was given a simple source of carbon (sucrose). In the second, the area received a complex source of carbon derived from organic materials including wood chips, sawdust, leaf compost, and poultry manure. The third treatment used no supplemental carbon. Tomato plants were watered every day with one of these three types of water or tap water for the control group. Two weeks and 6 weeks after planting, half of the plants were exposed to the pathogen Pythium ultimum.

Results showed that the growth of the pathogen was significantly inhibited by the treated water compared to the untreated water. The simple source of carbon treatment inhibited pathogen growth up to 90% compared to only 25% in the complex carbon source. Root growth, however, was adversely affected by the treated water.

The study suggests that greenhouses should blend their artificial wetlands water with fresh water to reduce dangerous accumulations of minerals to maintain a recommended balance of nutrients. "This dissolution, however," the authors noted, "may reduce the disease suppression potential of the treated water."


The complete study and abstract are available on the ASHS HortTechnology electronic journal web site:

Founded in 1903, the American Society for Horticultural Science (ASHS) is the largest organization dedicated to advancing all facets of horticultural research, education, and application. More information at


Original Article:

Effects of Using Water Treated by Artificial Wetlands on Root Rot Suppression and Tomato Growth
Nicolas Gruyer, Martine Dorais, Gérald J. Zagury, and Beatrix W. Alsanius
HortTechnology 21:759–766. [Abstract][Full Text][PDF]

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