US: Rapid Ebb and Flow Watering System deemed effective

Conventional overhead watering systems are found in many greenhouses where ornamental plants are grown. Though widely used, these traditional overhead systems have many drawbacks. To ensure that crops are completely saturated, the systems must use excess water, and studies have shown that up to 75% of the water and fertilizer applied can be wasted or leached from potted plants. Water, fertilizer, and pesticide run-off from overhead irrigation systems present risks to environments surrounding greenhouses.

Subirrigation methods such as "ebb and flow" systems are being tested in attempts to find effective and safe alternatives to overhead watering. Subirrigation systems have proven to reduce water and fertilizer waste in potted ornamental plant production operations. In these systems, potted plants are placed on benches or floors that are flooded to a depth of 2-10 cm. Capillary action in the plant substrate takes up water or nutrient solution through the base of the pots, and the solution is then drained from the bench or floor to a reservoir, resulting in no water lost to the environment and limited water loss due to evaporation.

Martin Gent from the Department of Forestry and Horticulture at the Connecticut Agricultural Experiment Station and Richard McAvoy from the Department of Plant Science and Landscape Architecture at the University of Connecticut recently examined a newly developed ebb and flow method developed by Geremia Greenhouse of Wallingford, Connecticut.

According to Gent, ebb and flow watering systems typically operate slowly so that the substrate takes up water to near effective water-holding capacity during irrigation. The research study, published in HortScience, tested a system that rapidly delivers water to and removes water from the production surface to restrict the water provided to the plants. The innovative short cycle irrigation process—called partial saturation ebb and flow watering (PSEFW)—restricts water uptake and can complete an ebb and flow cycle in as quickly as 4 minutes.

To determine the benefits and drawbacks of PSEFW, Gent and McAvoy compared the system with a control treatment of slow-cycle ebb and flow watering applied to geranium and chrysanthemum plants growing in pots on a flooded floor. "We measured water uptake per irrigation cycle and water and nutrient content of the root medium after repeated irrigation cycles," Gent said. "We also measured the vertical gradient and distribution of water and nutrients in the substrate and determined biomass and height growth and tissue nutrient composition as a function of watering treatment and location of pots across a flooded floor."

According to the results, the PSEFW system reduced water and fertilizer use by 20% to 30% compared to the slow-cycle watering method. Biomass and stem height at bloom were also reduced by 10% to 20% under fast-cycle saturation. The PSEFW method did not affect the rate of flower development or plant nutrient composition.

Gent and McAvoy emphasized the benefits of the PSEFW method for both ornamental plant producers and greenhouse neighbors. "The increased water and nutrient use efficiency will result in the use of less fertilizer and water," they said. "This will benefit growers by lowering production costs." They noted that another benefit of PSEFW is that the substrate never approaches the effective water-holding capacity, so plants are not exposed to a high water content that can cause root disease. "The ability to repress disease should encourage growers to adopt ebb and flow methods that recycle all the excess water applied to the plant. This will benefit society and protect natural resources and the environment from pollution resulting from the application of excess fertilizer."

Gent and McAvoy concluded that the PSEFW method shows great promise as a means to produce uniform crops of container-grown plants while conserving water and fertilizer.

The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/cgi/content/abstract/46/5/791