Should Farmers Inoculate?

There are varying opinions on this. So, what factors should we consider when trying to make a decision? The first thing to consider is cropping history. Data shows that adding an inoculant might not be necessary in the 5 years following the first planting of soybeans in that field.

Soil factors are also important when considering inoculation. Soil moisture, pH, salinity, IDC, and nutrient levels all play a role in rhizobia levels in the soil. One factor Dr. Geddes particularly stresses is the levels of nitrogen in the field. Research has shown that planting soybeans in fields with high residual nitrogen causes the nodules in soybeans to become lazy. In this scenario the soybeans will rely on the nitrogen source within the soil instead of growing functional nodules.

One thing that Dr. Geddes hopes to see in the future is a chemical AND biological soil test. This would look at levels of rhizobia in the soil, as well as distinguish which strains of rhizobia are present.  This would allow farmers to make their inoculating decisions based on actual field data. When working with this soil testing technology they have witnessed the rhizobium competition problem in some of their soils. Most soils have native rhizobia, however some species are more effective at fixing nitrogen than others. A problem arises when these ineffective rhizobia outcompete the beneficial rhizobia, filling the plants with nodules that are unable to produce nitrogen effectively. Therefore, inoculating may be necessary even when high levels of rhizobia are present in the soil.

All of this to say, there is still lots of research needed around the topic of rhizobia and inoculants!

 Can we enable a rhizobia/plant relationship in cereal crops?

This is something scientists are still working to figure out! Currently, there are three different scientific approaches to make this happen:

1.       Modify plants to express the enzyme needed to fix nitrogen. This would allow the plants to fix nitrogen regardless of the amount or type of bacteria in the soil.

2.       Get cereals to produce nodules with the ability to create the necessary relationship between the plant and the rhizobia. This would create a legume-like plant, meaning we would still be reliant on inoculation and soil rhizobia loads for effective N fixation.

3.       Get bacteria that is already interacting with the cereal roots to fix nitrogen.

Biologicals have gotten us close to method 3. Products such as Envita, Utrisha and Proven can already be used on some crops to allow for a small amount of atmospheric nitrogen fixation during the growing season. While these products won’t be able to completely replace synthetic fertilizers, they do help to reduce our reliance on them. So far in trial data these products also seem to give the crop a yield bump. However, one of the reasons these products have been slow to adoption is their variability. Trial results have not been consistent thus far, making it hard to discern their benefit and effectiveness.

 For more in depth data, watch Dr. Geddes’ presentation here: MAC 2022 - Biologicals for crop nutrition - YouTube

-Beth Ens