Inoculate those beans
by Lyndon Brush 

High prices encourage sod busting with soybeans. If you go from grass to crops, make sure to watch soil fertility. And inoculate those seed beans. 
When soybean prices go up, they trigger producers to think about the possibility of planting soybeans on ground that has been in a permanent cool-season forage crop. Expiring CRP acres also become soybean converts. Of course, the reasoning is to take advantage of the high soybean price and oftentimes, after row cropping for a few years and watching the soybean market return to earth, producers return these fields back to a forage crop.

Planting in these situations can work effectively and can be a good way to reintroduce a new forage species after row cropping a few years, but you need to do some homework to avoid problems.

Quick Facts • Pasture and CRP converted to soybeans may not have enough soil bacteria for proper nitrogen fixation in legumes. • Inoculating soybean seed adds rhizobium bacteria. • If you convert pasture or CRP to crops, start with soil testing.

Time to test
From an agronomy perspective, there are a few issues to address. You should take soil tests to addresses any soil pH and fertility issues, and you have to have a plan for controlling the existing vegetation through proper herbicide burndown programs or tillage operations. The simplest problem to avoid, but one that can get overlooked is the use of soybean inoculants applied on the seed at planting time. Inoculating soybeans used to be standard practice, but since soybeans have become so much part of a traditional crop rotation the inoculation process tends to be forgotten.

Legumes like it
Soybean plants require a large amount of nitrogen to grow and produce seeds. Soybeans, being a legume, have the ability to fix their own nitrogen from the atmosphere through interaction with rhizobium bacteria. We call it a symbiotic relationship. The bacteria produce nitrogen for the soybean plant while the soybean plant provides a place for the bacteria to live. But legume species require specific rhizobium bacteria. Make sure the rhizobium inoculants that you purchase are specific to the legume crop you are trying to grow.

When to inoculate
The rule of thumb is that if a field has been out of production for several years, you need to inoculate the soybean seed. This will at least ensure that the proper bacteria have been added to the soil. The definition of “several years” may be open for discussion, but, in reality, the cost of adding the bacteria is minor compared to trying to grow plants without it. A field that is pale green with limited plant growth and limited pod development can be extremely costly in any year—especially if adding a soybean inoculant at planting time could have prevented it. With input costs on the rise, good growth is all the more important.

There are many different ways to add bacteria to the seed. Inoculants are available as a dry, liquid or frozen product. Take a look at the type of product which meets your needs and apply according to the label directions. Keep in mind that if you treat soybean seed with a fungicide seed treatment and also want to add a rhizobium inoculant, you must add an extender product to enable the live bacteria to survive on the soybean seed.

Lyndon Brush is a staff agronomist for MFA Incorporated.

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