"Less is more" approach to water use may be key to nursery efficiency
If growers can group plants by similar water needs, they can be more efficient in their water application and save energy and money.
Michigan’s unpredictable weather rarely makes things easy for farmers, and container nursery operators are no exception.
These growers cultivate plants in individual, above-ground pots, giving them less soil to work with when trying to achieve optimal water and nutrient levels than growers of in-ground plants have. Further, to contend with problems caused by the extreme rainfall Michigan can receive during the growing season, nurseries use potting mixes (also known as substrates) designed to drain quickly and avoid flooding plants during periods of high rainfall.
Although effective in preventing plants from drowning, this practice – particularly in large operations -- can create other issues, such as water use inefficiencies and fertilizer runoff. To address these challenges, Michigan State University (MSU) AgBioResearch scientist Tom Fernandez is researching irrigation management and water quality issues for the industry.
“Nurseries end up irrigating every day when it’s hot in the peak growing season,” said Fernandez, an associate professor in the MSU Department of Horticulture. “Because of daily irrigating and the way substrates are designed, it’s easy to overwater. Since this water drains out, it doesn’t cause any major stress to the plant, but it does result in wasted water.”
To assess water use levels and their effect on plant growth, Fernandez conducts experiments using sensors to measure the daily water use (DWU) -- the amount of water used by a plant in 24-hours through both transpiration and evaporation. He waters one group of plants with a set amount of water daily, similar to the practice of many nurseries. Another group of plants receives 100 percent DWU the first day, and 75 percent the next. The final group of plants receives 100 percent DWU the first day and 75 percent on the second and third days.
Fernandez said his findings show that there are no significant differences in plant growth despite the water deficits, and slightly reduced growth occurred in only two or three of the 40 species tested.
“When we determine how much water to apply, we also know how much water the plant is actually using,” Fernandez said. “This information allows nurseries to group plants on the basis of their water requirements. That’s difficult for growers because they might start growing plants at certain times or ship certain plants at certain times and they’re growing them all in one big block, so plants are being shifted in and out, but we certainly suggest that they try. If growers can group plants by similar water needs, then they can be more efficient in their water application and save energy and money.”
In addition to increasing nursery efficiency, Fernandez believes improved irrigation scheduling can reduce negative environmental impacts. For example, his findings showed that reducing the amount of irrigation applied reduces nitrates and phosphates in runoff.
“Runoff water has to go somewhere, and it’s going to carry nutrients with it and – potentially -- it’s going to go off-site,” he said. “As a result, problems with eutrophication can develop, where nutrients get in the surrounding water systems and cause accelerated microorganism growth. Algae and other microorganisms start growing so quickly that they deplete the oxygen in water sources or the surrounding water. In certain cases, this can cause environmental problems, including decreased biodiversity and toxic conditions for aquatic life.”
Fernandez added that an increasing number of nurseries are recycling runoff water and that nutrients in runoff need to be managed properly to ensure quality plant production. An upcoming study will look at how reduced irrigation affects not only nitrates and phosphates, but pesticides.
“Most pesticides are broadcast over the top of plants, not applied to the soil like fertilizers,” he explained. “So when they are applied, they hit the plants and substrates – target areas – in addition to the production surface the plants grow on – non-target areas. Then, when irrigation is used, pesticides could be introduced from those non-target areas into the runoff stream if not managed properly.”
Fernandez plans to conduct the pesticide research as part of a collaboration developed several years ago with horticulture researchers across the country. The group has obtained a planning grant and is also applying for a full U.S. Department of Agriculture Specialty Crop Research Initiative grant.
“It’s really a nationwide perspective that we’re shooting for here,” Fernandez said. “This is our first official year, and we’ve already been pretty productive. What I do links up with what other people are doing so no one is working in a box.”
In addition to support from USAID and AgBioResearch, the Fernandez’s research has received funding from Project GREEEN (Generating Research and Extension to meet Economic and Environmental Needs), the state’s plant agriculture initiative at MSU, and the U.S. Department of Agriculture National Research Initiative.