Tips for Innoculating Arbuscular Mycorrhizal Fungi on Your Farm

Tips for Innoculating Arbuscular Mycorrhizal Fungi on Your Farm

Welcome to Tips Tree Planting’s guide on how to inoculate arbuscular mycorrhizal (AM) fungi on your farm! For the past 8 years, we have partnered with the USDA-ARS to develop an on-farm AM Fungus Inoculum Production System. Our goal is to make the economic and environmental benefits of mycorrhizae accessible to more farmers. In this article, we will share everything you need to know to start your own on-farm system.

AM fungi basics

Related Posts: bone meal for phosphorus addition

Arbuscular mycorrhizal (AM) fungi are crucial for agricultural ecosystems as they colonize most crop plants. These fungi are obligate symbionts, relying on a mutual relationship with plant roots to survive. In return for sugars, the fungi extend a plant’s root system and improve its access to immobile nutrients like phosphorus, zinc, and copper. Mycorrhizae can explore a larger volume of soil than plant root hairs, enhancing plant growth and yield. They also increase disease resistance, improve drought tolerance, and enhance soil structure.

AM fungi inoculum

Inoculating with mycorrhizal fungi offers another way to benefit from their advantages. Mycorrhizal spores, pieces of colonized roots, and viable mycorrhizal hyphae act as active propagules that can infect other plants with AM fungi. Using inoculum can be preferable in situations where standard agricultural practices have negatively impacted mycorrhizal populations.

Commercially produced inoculum is available but can be expensive for farmers. Our research aims to develop an on-farm inoculum production system that is potent, effective, and inexpensive. By avoiding the costs of commercially produced inoculum, more farmers can access the benefits of AM fungi.

On-farm production of inoculum

Our on-farm system starts by planting “host plant” seedlings into bags filled with a mix of compost, vermiculite, and local field soil. The AM fungi present in the field soil colonize the host plant roots, and as the host plants grow, the mycorrhizae proliferate. The mycorrhizae overwinter in the compost and vermiculite mixture, making the inoculum ready for use in the spring.

Choosing the right host plant is crucial, and we recommend using bahiagrass, a member of the grass family, as a general host. Bahiagrass is frost-killed, preventing it from becoming a weed pest in the field. To establish bahiagrass seedlings, germinate the seeds in vermiculite or seed starter in the greenhouse. Four months before the last frost date, transplant the seedlings into conical plastic pots filled with a sand and soil mixture. These pots produce seedlings with a long root system, optimizing their contact with propagules deep in the bags.

The medium used to plant the host seedlings is essential. Compost diluted with a nutrient-poor substrate like vermiculite, perlite, or peat has been successful in producing mycorrhiza inoculum. The optimal compost dilution rate and type of diluent depend on the species of AM fungus and the compost used. We generally recommend dilution ratios between 1:3 and 1:9, and we use a 1:4 dilution with yard clippings compost.

Field soil is mixed into the medium as an inoculum starter. Collect soil samples from natural areas of the farm, like wood lots or fence rows, to ensure a diverse and healthy mycorrhizal population. Sieve the soil to remove rocks and roots and add 100 cm3 of soil to each bag. Transplant four to five bahiagrass seedlings into each bag as soon as possible after the last frost.

Throughout the season, the bags require minimal maintenance. Water as necessary and remove weeds to avoid introducing weed seeds into the inoculum. At the end of the season, when the host plants senesce, the mycorrhizae sporulate. The spores overwinter in the compost and vermiculite mixture, ready for use in the spring.

Harvesting inoculum

To harvest the spores and viable hyphae, cut off dead leaves, remove the root ball from the bags, and shake off the medium into a large bin. Cut the root system into pieces and mix them into the inoculum. The resulting inoculum is then ready to be mixed with potting media in the greenhouse.

Producing colonized seedlings for outplanting

When adding inoculum to potting mix, consider both the potency of the inoculum and the volume of the cells. A small amount of inoculum is sufficient per cell, and we recommend using a lower dilution rate than needed. This ensures a heterogeneous mixture. The dilution rate depends on the cell size, with a 1:9 dilution suitable for cells that are 50 cm3 or smaller.

Adapting greenhouse practices

Greenhouse fertilization regimes need to be modified to accommodate the symbiosis’ sensitivity to phosphorus levels. For conventional growers, we suggest a standard potting mix supplemented with a balanced nutrient solution low in phosphorus. Organic growers face more challenges, but using an unaltered potting mix or adjusting compost levels can help manage phosphorus levels.

Getting your system going

The benefits of inoculation can vary from year to year and between cultivars. However, when the symbiosis offsets factors that depress yields, the gain can be significant. Our low-cost on-farm system is easy to integrate into any farming system. Plan ahead, as a full season is required to produce the inoculum.

For a detailed step-by-step guide and further reading, visit Tips Tree Planting and check out our Quick and Easy Guide to On-Farm Mycorrhizae Inoculum Production. Start harnessing the benefits of arbuscular mycorrhizal fungi on your farm today!

Related Posts: raised bed preparation for planting