Further indications of the benefits of mycorrhiza

Should you select organic or inorganic fertilizers to grow containerized plants in mycorrhiza-inoculated fertilizers? Do fertilized plants grow better in media containing mycorrhiza?

A recent study by Texas A&M University researchers reveals new benefits in incorporating the fungal organisms in growing media. Among them: Because mycorrhiza increase nutrient uptake by plant roots, less leachate may be present in growing media for runoff into the nursery.

Lucilla Amaya Carpio, a graduate student at Texas A&M University, conducted the study under the guidance of A&M professors Drs. Fred Davies Jr. and Michael Arnold.

In the study, to be published in the Journal of the American Society for Horticultural Science, plants grown with an inorganic controlled-release fertilizer plus mycorrhiza performed better than plants treated with the fertilizer alone and with an organic slow-release fertilizer with and without the fungal organism.

"The dogma that AMF [abuscular mycorrhizal fungi] are better for OSRF [organic slow-release fertilizer] than ICRF [inorganic controlled-release fertilizer] does not always hold water," Davies told The Post.
The study was conducted in a realistic nursery setting during the late summer months when temperatures in containers reached 112 degrees F. The researchers measured plant growth, marketability and leachate of bush morning glory (Ipomoea carnea subsp. fistulosa) growing in 2-gallon containers. Though several fertilizer formulations were used in the experiment, P (phosphorus) levels were equalized. High fertility, particularly P, will depress AMF.

"However," Davies added, "AMF does very well with slow-release fertilizers."

"We need to get away from big plant vs. small plant mentality," Davies said. In a nursery setting (PUT BREAK HERE)with optimal fertilization and watering, a grower should not expect to see larger AMF plants, he said.

"However, if the AMF is allowed to colonize, which they can under commercial nursery production sites, then it might mean you have a plant which has greater stress resistance - requiring fewer pesticide treatments during production - and a more marketable, 'valued-added' plant that does better in a landscape site," Davies said.

The best growing media for AMF is often a mineral soil, he said, but AMF does "just fine" in a 20 percent sand - 80 percent bark medium, a popular nursery mix, he said.

The researchers suggest that because the larger-sized AMF plants had higher total leaf tissue nitrogen, phosphorus and potassium, the greater nutrient uptake and utilization would reduce the potential risk of leachate runoff. In recent years, growers under pressure to reduce runoff have incorporated BMPs - best management practices - into their operations.

"While AMFs are not a panacea, they do have their niche and they do work," Davies said. "As we continue to apply BMP to improve pesticide, fertilization and water usage, there is every reason that the 'niche' of incorporating AMF - as a part of the system - will continue to increase."