By Stefano Pinna, Poultney Mettowee Natural Resources Conservation District
When seated on top of our tractor, we often aren’t thinking about what’s underneath our wheels. Farmers have an intricate understanding of when it’s a good time for tilling, how the soil should feel when it’s time to plow, disk, or pass with a chisel, but may not be as concerned with the complicated and intricate interaction between fungi, bacteria soil microbes, and the plants we are growing.
Assemblages of fungi, bacteria, and roots are communicating, a little bit like our phones and computers do, transmitting chemical signals one to the other, exchanging and trading minerals, nutrients, and organic compounds.
Among these microscopic creatures, mycorrhizae have proven to be one the most interesting for agricultural production. Mycorrhizae are beneficial fungi that work as extensions of plant roots. They colonize the outer layer of the root, forming a shrub-shaped structure and extend their small tentacles, named hyphae, to reach nutrients in the soil. Through this partnership or symbiosis, plants can trade some of their carbon (5-20%) with nutrients collected by the fungi (like nitrogen and phosphorus). Hyphae are very effective in enhancing plant nutrient uptake thanks to their diminutive size (4 to 5 times smaller than roots) that allows them to reach small pores and trapped nutrients, their ability to explore soil (up to 330 feet of hyphae per 0.06 sq inch), and store soil nutrients in sack-like structures for later use.
Mycorrhized roots have an affinity for phosphorus and can absorb it almost twice as fast compared to non-mycorrhized roots. Moreover, mycorrhizae infiltrate a large volume of soil and allow plant roots to adsorb phosphorus located far away from them. Some research has found that mycorrhizal roots were able to intercept phosphorus placed almost one foot away.
Eighty percent of commercial crops can establish a symbiotic relationship with mycorrhizae, the exception being the Brassicaceae plants such as broccoli and canola. Mycorrhizae thrive on minimally disturbed soils like no tilled or minimum tilled soils, but they suffer with deeper tillage because it disrupts the network of connections, breaking them apart and dispersing hyphae and fungus in the soil profile. Mycorrhizae take great advantage of manure applications and every other amendment that improves soil.
Mycorrhizae are used commercially today especially in vegetable production, but very little research has been conducted on row crops such as corn or soybeans. Many commercial products are now available on the market and can be either sprayed as water mixes or added to the seeds as a powder. Research shows that most of these products can be effective in increasing phosphorus uptake, especially on soils where P fertilizers have been applied at low rate.
Could these mycorrhizae be an added defense to reduce phosphorus loading to Vermont surface water? Potentially, a healthy web of mycorrhizae could unlock some of the phosphorus present in the soil in unavailable forms (99% of all P in the soil is unavailable for immediate plant uptake) reducing needed phosphorus applications, with positive consequences for the environment and reduced fertilizer costs for farmers. References for this article include (Fleming, 2014), (Bolan,1991) and (Hattingh, 1973).