Legume Inoculation Important for Legume Establishment

Among the required nutrients for plant growth, nitrogen is number one element that is required in large quantities for high levels of forage production. Deficiency of nitrogen is a common limitation to forage and livestock production systems. 

In the atmosphere, 80 percent of its constituent is nitrogen. On the other hand, an acre of land has an estimated 37,000 tons of nitrogen above it. Nitrogen present in the atmosphere is in the form of an inert gas, and plants cannot take this form of nitrogen for their use.

Plants get their essential nitrogen from different sources. These include soils, organic matter, free-living bacteria in soils, blue-green algae, organic manure and compost and rainfall. The most common source of nitrogen is commercial fertilizers, such as urea, ammonium nitrate and ammonium sulfate. 

Legume plants are a great source, which can also produce substantial amounts of low-cost natural nitrogen. This reduces the cost of forage production by mitigating commercial nitrogen fertilizer use.

Legume plants have the unique ability to capture atmospheric nitrogen and fix them to their roots, called nodules, in the soils. Nitrogen fixing bacteria, Rhizobium, live in the roots of legume plants and fix nitrogen in usable form for plant growth. Nitrogen produced in the roots can be used by the legume plants for their own growth, by the associated grasses or by other crops grown in rotation with legumes.

For good and greater nitrogen fixation, it is important to have large numbers of live Rhizobium bacteria near the root zones of legume plants. To assure this, inoculating seeds of legume before planting is a common practice.

Species-specific or variety-specific bacteria are needed to inoculate seeds for proper nitrogen fixation. 

For example, alfalfa seeds should be inoculated with alfalfa-specific bacteria, and sainfoin seeds should be inoculated with sainfoin-specific bacteria, etc. Remember that sainfoin bacteria will not work for alfalfa and vice-versa.

Bacterial inoculants are commercially available to purchase. 

Sometimes, legume seeds are coated with the right Rhizobium bacteria. 

It is recommended that a producer should check several things before any purchase is made. First, legume plants to be inoculated are specifically listed on the packet, and the expiration date is still valid and not expired. In case of storing, inoculants should be stored in a reasonably cool place, meaning between 40 and 70 degrees Fahrenheit or refrigerated, and out of direct sunlight. 

It is advised not to leave the inoculants in the heat of a pickup truck or similar open locations. This may result in failure of stand establishment or a poor stand.

Anowar Islam is an assistant professor and the University of Wyoming Extension Forage Agroecologist in the Department of Plant Sciences in the College of Agriculture and Natural Resources. He can be reached at 307-766-4151 or mislam@uwyo.edu.