Should I inoculate my soybeans?
Figure 1. Nodules formed due to the symbiotic relationship between soybeans and a nitrogen-fixing rhizobia bacteria call Bradyrhizobia japonicum.
This is Dr. Nathan Mueller, Nebraska Extension Cropping Systems Educator in Fremont, NE. The warm weather has farmers gearing up for planting season or at least thinking about it. This warm air causes the frequency of certain questions to rise too. One question is “Should I inoculate my soybeans.” The sarcastic response you might get from me is “with what?”
It is generally understood that we are talking about adding a nitrogen-fixing rhizobia bacteria call Bradyrhizobia japonicum, that through a symbiotic relationship with the soybean plants allows for the conversion of nitrogen gas to plant available nitrogen where by the bacteria get some sun-derived energy back. Overall, everyone including you the farmer is happy since about 50 to 70% of nitrogen needed by soybeans is provided by this relationship and the rest from the soil.
Getting back to the question about the need to inoculate. Before I respond yes or no, I will ask you four questions:
- Has it been more than 3 to 5 years since you last planted soybean?
- Is your soil pH below 6.0?
- Do you have sandy soils?
- And has your field flooded for more than a week?
If you answer yes to one of more of the questions, I am apt to say yes to inoculating soybeans because these factors can reduce the population of these beneficial bacteria for nitrogen fixation.
If you answer no to all the questions, then I will say no. And here is why. An 8 year-long study from 2000 to 2008 across Nebraska, Iowa, Minnesota, and Indiana evaluated 51 different inoculant products in 73 experiments. And guess what they found. Regardless of price or ease of inoculant application, fields with a recent history of soybeans don’t benefit. The average yield response was 0%.
For more information about inoculating soybeans, contact me at the Dodge County Extension Office at 727-2775. To listen to this radio message again, visit our local website at croptechcafe.org. This is Dr. Nathan Mueller, Nebraska Extension Cropping Systems Educator on KTIC radio.
