Although the planters have not officially started rolling in Illinois, it is safe to say that soybeans will most likely win the battle for most acres in 2018. With this being the case, many acres across the state will be coming off a continuous corn rotation and either going back into a more traditional corn-soybean rotation or going to continuous soybeans. One important detail that will be overlooked this planting season is treating soybean seed with inoculant on these acres.

Why do we inoculate soybeans? Soybeans require 4 – 6 pounds of nitrogen per bushel produced. That’s almost 3 times what a corn plant needs on a per bushel basis. We are fortunate enough that soybeans fixate their own nitrogen from a symbiotic relationship with B. rhizobia japonicum, a species of legume-root nodulating bacteria. Common field conditions that can reduce or eliminate background rhizobia populations in the soil include low organic matter, low (acid) pH, high EC (salinity), repeated freeze-thaw cycles and, in the case of this topic, long crop rotations without soybeans.

With a long corn-on-corn crop rotation (3 – 5 years) it is not uncommon to see a yield drag in the first 2 years of soybean production because of the lack of nodulation. With the addition of an inoculant, growers could see a potential 2- to 3-bushel yield addition if the bacterium is a limiting factor. Inoculants can also provide nutrient use efficiency, stress mitigation and overall better plant health.

If you are considering using a soybean inoculant this year, there are several ways to get them in the soil profile. They are directly on the seed, in-furrow and dry planter box treatments. The first of the three is by far the most effective and convenient. By putting the inoculant on the seed, you are ensuring that the bacterium will contact the roots. In-furrow applications are also effective, as they are usually put in with high volumes of carrier. As a last-minute treatment, a dry planter box inoculant can also be used. Below are some products that are used for each application.

On-seed Inoculant
Preside^® CL
Optimize^® 

In-furrow Inoculant
In-take 

Dry planter box treatment
Graph-Ex SA^®

Most soybean inoculants come at a relatively small marginal cost per acre, when you consider the bushels you could be missing. You can treat an acre with an inoculant for anywhere from $4 – $8 per acre. Nitrogen fixation is an amazing process and saves us thousands of dollars on a supplemental nitrogen program in soybeans. However, we as growers must make sure that we are sustaining healthy and viable populations of rhizobia on our acres. With no definite way of “counting” bacterium or even nodulation, inoculating on a corn-on-corn breakout would be a wise investment.

Prins is a Sales Agronomist with The Equity at their Greenville location. He grew up on his family’s corn and soybean farm in Northwest Illinois. Aaron has been a Certified Crop Advisor since graduating college in 2015. He and his wife, Samantha, have twin sons, Eldon and Victor. Aaron is very involved in his local Farm Bureau as well as his Church.