Maintaining a balanced fertility program involves providing the proper nutrients to plants at the proper time and compensating for any nutrient leaching. Taking a few planning steps before your crops get established and continuing to monitor nutrition can help prevent fertility problems before they happen.
A few things you can do to maintain a balanced fertility program are complete routine water testing, monitor growing medium for pH and EC levels, select crops wisely and automate irrigation and fertigation processes.
Complete Routine Water Testing
Before setting up a fertility program, greenhouse growers need to test their water, says Stephanie Burnett, associate professor of horticulture at the University of Maine. Water quality can have a major effect on maintaining a balanced fertility program and water pH and alkalinity need to be monitored and evaluated.
Water quality can be a regional issue in some states. Burnett says greenhouse growers in Maine seem to have more problems with high pH and/or high alkalinity and they can have difficulties managing those water properties.
“The pH and alkalinity of the water should be tested at least once a season depending on the water source,” she says. “pH and water alkalinity of the water will likely be more stable if it comes from a municipal source than from an aquifer that can change with seasonal precipitation levels.”
Small- to mid-sized growers can receive different recommendations from fertilizer manufacturers for each of the crops they are growing, which can be a real challenge. It can be difficult for growers to figure out which fertilizer regime works best, especially if they’re producing multiple crops.
“If growers are managing their irrigation carefully, then most of the nutrients should be lost through plant uptake,” Burnett says. “Growers who produce a monoculture crop, such as greenhouse tomatoes, greens or an ornamental crop, should have it much easier maintaining a balanced fertility program since they are only producing one plant species.”
Test Growing Medium pH And EC Regularly
Growers should be checking the electrical conductivity (EC) of their growing medium at least once a week using a testing method like the PourThru technique, Burnett says. She says more growers probably check it less often than weekly.
Irrigation system can also have an impact on the fertility program.
“The growers who are using conventional irrigation systems, such as overhead or a drip system, are applying twice as much fertilizer compared to unconventional systems such as ebb-and-flow,” she says. “This makes it particularly important to check EC and pH because a single fertilizer application can cause a greater change.”
Burnett advises growers who have an ebb-and-flow system to check EC and pH at least once a week, too. Ebb-and-flow irrigation can lead to a high EC in the top few inches of the root zone, but a normal EC in the rest of the root zone. Pour-Thru soil testing can leach the salts down through the root zone. Stick probes can help growers be sure they are measuring the EC at the bottom of the medium instead of the top.
Growers who produce crops with recirculating irrigation or hydroponic systems are likely checking EC more than once week.
Select The Right Crops For Your Operation
Burnett says those growers who aren’t set up to provide the right pH, EC and fertility program might want to consider not growing more sensitive crops.
“Growers may want to avoid the plants that are more difficult to grow unless they can receive a really good margin, making them worth the extra effort it may take to grow them,” she says. “Calibrachoa can be a tricky crop for some growers because it commonly develops iron deficiency when the substrate pH is not low, but it seems to be worthwhile for them to grow. For difficult crops like calibrachoa, growers can choose a fertilizer that works for most crops and then have an acid and a basic fertilizer available to increase or decrease the pH as needed.”
Automate Irrigation And Fertilization
Accurate measurement and automated irrigation and fertigation can be a huge benefit to a balanced fertility program. Burnett is currently at the University of Georgia working on a project with horticulture professor Marc van Iersel and scientists at Decagon Devices in Pullman, Wash.
Van Iersel is developing a system to automate both irrigation and fertigation. Decagon sensors are being used to measure EC and water content in the growing medium. Two delivery lines, one for water and one for fertilizer, go directly into a Dosatron injector. Sensors measure the water and EC and the system provides whatever the plants need.
Burnett says Decagon is releasing an irrigation control system that growers can use to measure EC.
“This new system won’t be able to control fertigation, but growers could use it to turn their fertigation system on and off based on EC readings from Decagon’s new controller,” she says.
For more, contact Stephanie Burnett, University of Maine, Department of Plant, Soil, and Environmental Sciences; (207) 469-8244; firstname.lastname@example.org.