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Lancaster, OH | Soybeans require approximately 5# of nitrogen for every produced bushel (3.8# crop removal plus stems, roots, leaves, etc.). So, for a yield of 50 bushels, 250# of N are needed, 60 bushels 300#, etc.
There are only 3 places the N can be obtained without applying fertilizer. Carry over nitrogen from the previous year's crop, release of organic in from the soil or Bradyrhizobium japonicum. Since we have a difficult time getting 200# in corn to last for the season and organic N is low and slow, the bacteria is the only real source.
B. rhizobia is not very durable in the soil. Anaerobic conditions from soil saturation, high or low pH or drought conditions in the top layers of the soil do not allow for their survival. Additionally, the roots of the soybean plant and B. rhizobia have to be in virtual contact with one another to form nodules.
That's a lot of information but, it is easy to see that in rotations, especially in long rotations, inoculation is important when planting soybeans or other legumes.
I would recommend our seed applied pre-inoculant. It would give you a very large number of rhizobia per seed compared to hopper box or other inoculants. In long rotations, many will recommend a pre-inoculant plus a hopper box (usually peat based) product. This works very well. However, if you are using a planter with a monitor, peats can cause monitors to mis-read seed drop.
If you use a pre-inoculant, use one that incorporates an extender and applies at least 1 million cfu (colony forming units) per seed. Those that apply less or do not incorporated extenders will give you disappointing results.
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Inoculate soybeans after 4 yrs COC?
