Controlled-release fertilizers (CRFs) can provide growers with cost-effective, sustainable options for nutrient delivery in the greenhouse.
Water soluble fertilizers (WSF) have long been growers’ primary choice for nutrient delivery in commercial greenhouses, but that may change in the future. A resurgence of interest in controlled-release fertilizers (CRF) is occurring as greenhouse growers hunt for sustainable, cost-effective solutions for fertility management. Recent research conducted at Purdue, Cornell, and the University of New Hampshire on bedding and potted plants confirms that CRFs have the potential to play a much larger role in large-scale greenhouse production in the future.
“Generally speaking, the research is promising,” says Dr. Brian Krug, greenhouse/floriculture extension specialist for The University of New Hampshire. “For almost all of the controlled-release products we are using, we are seeing similar growth patterns in the dry weights of the controlled-release plants when compared to the water soluble controls. This is for a target rate of 8-9 lbs/cubic yard, anything below 6 lbs/cubic yard with a CRF alone shows a reduction in quality and dry matter.”
According to Krug, CRFs are worth growers’ consideration because new technologies have made them easier to use and control. Additionally, their overall cost (depending on application rate) is less than WSFs, waste and leaching reductions occur, and they contribute to consumer success.
“If you look at the last five to ten years, one of the biggest changes to CRFs is in the size of the prill, which makes it easier to get uniform distribution for greenhouse crops,” says Krug. “Improvements to the polymer coatings over the years have made the products more predictable and stable to use in the greenhouse.”
“The research we have done so far shows that less nutrients are being lost from the bottom of the pot due to leaching,” says Krug. During experiments on poinsettias, gerberas and cyclamens, the amount of nitrogen in the leachate gradually increased during the WSF production period and gradually decreased for CRF treatments.
The upfront cost for CRFs may seem prohibitive, but in terms of overall price, they pay off. For the poinsettia experiment, researchers used 150 ppm of liquid feed at a cost of $3.26 ($40.35/25 lb bag) to fertilize 100 (4-inch) containers for the entire season. For controlled-release products, the cost was between $0.70 and $1.03 ($100/50 lb. bag) and the growth quality was the same.
Shelf Life and Consumer Success
“CRFs can enhance shelf-life, particularly for hanging baskets and combination containers,” says Krug. “You are also providing some long-term nutrition for the consumer. This may be an intangible benefit that you don’t see right away, but repeat sales can occur if your customers have more success with your products than with competitors who are not using CRFs.”
“Controlled release fertilizers show a lot of promise. However, like everything else, results will vary based on crops, growing parameters and environmental conditions,” says Krug. “It is always a good idea to give things a good trial on a small scale to see if these products work well for you and your systems.”
Note: For more information on the controlled-release study, refer to the August 2012 issue of Greenhouse Grower or contact Brian A. Krug (firstname.lastname@example.org), Neil S. Mattson (email@example.com), Roberto G. Lopez (firstname.lastname@example.org), or Christopher J. Currey (email@example.com).
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