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Agronomy Update

What are Inoculants and Should I Use Them?

Published on Monday, April 3, 2017

Do you know what the most abundant element in the air is? It’s not oxygen. It’s not hydrogen. It’s actually nitrogen (N). That’s right, one of the biggest input costs on your farm is actually floating around in the air you’re breathing. But since it’s a diatomic molecule (N2=gas), your corn crop can’t access it. Therefore, you have to buy and apply it to your crop. Soybeans, on the other hand, are legumes which means they can capture that free-floating N gas and, with the help of some soil microbes, convert it to a usable form of N.

That helpful soil microbe is called Bradyrhizobium japonicum and it does all the heavy lifting for the soybean plant. It has a symbiotic relationship with the plant, which means that they both benefit from the arrangement. The soybean plant feeds the microbe with energy and, in return, the microbe feeds the soybean plant with N. It’s a win-win for both parties. If you’re like me, you’re probably thinking this is pretty cool, but what does it have to do with inoculating soybeans? It has everything to do with it. There are always native populations of Bradyrhizobium japonicum in the soil, but sometimes there aren’t enough of the little guys to get the job done. When you inoculate your soybeans, you’re actually adding those living microbes to the soil. This is why you never want to leave your inoculant out in the sun or exposed for too long.

Most research confirms that applying an inoculant to your soybean crop every year is not cost effective and will usually not provide a positive return on investment. However, there are some instances that I believe it will pay to add an inoculant. The first is if a field has been out of a soybean rotation for more than three years. Because rhizobacteria is host specific, it will not survive extended periods of time without a soybean crop. The second instance where inoculants could prove beneficial is if you’ve experienced prolonged periods of flooding with standing water on the field. Because those microbes are living organisms, they need oxygen. And when your soils are saturated, that oxygen source is cutoff. A third time it pays to apply an inoculant is if your soil pH is way off. If your pH is below six or above seven, the viability of the native microbes decreases and can benefit from the addition of an inoculant.

Believe it or not, soybeans require much more N than corn does to produce a bushel of grain. But through their mutually beneficial relationship with Bradyrhizobium japonicum they can use what’s already available in the air to supply the bulk of their needs. For more information on soybean inoculants and whether your operation could benefit from adding one, please contact your local Beck’s representative.


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Author: Austin Scott

Categories: Agronomy, Kentucky, Tennessee


Austin Scott

Austin Scott

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