19 Jun Do I Need to Inoculate Soybean or Pulse Crops Every Year?
We have been getting a lot of questions lately about the need to inoculate your crops every year. Is it necessary? If I added bacteria last season, isn’t there enough bacteria already? If I add bacteria every year, won’t I eventually get enough bacteria that I won’t have to add anymore? And if I am using added nitrogen to the soil it should still have some so why wouldn’t my nitrogen fixation levels be high enough for my plants?
Here’s why adding bacteria every year is important:
Rhizobium populations will decline as more time passes, so by inoculating every year you ensure a robust population of bacteria are in your soil. This will replenish the soil bacteria population that was lost since the last season. It also ensures that the bacterial population in your soil is composed of vigorous & healthy microbes that can give their optimum nitrogen fixation performance. Not only maintaining an optimum number of soil bacteria is important but also the quality of the soil bacteria.
Changes in soil pH and moisture levels throughout the year can also negatively affect your rhizobia populations. Rhizobia are very sensitive to soil pH, and are most successful at forming nodules in soils with a pH between 5.5 and 8. Soil pH levels outside of this range can stress rhizobia and lead to lack of nodulation. Soil flooding and excess moisture can kill your bacteria quickly as well. Nitrogen-fixing bacteria found in inoculants are aerobic and/or micro-aerophillic which means they need oxygen for respiration. In water-logged or excessively wet soil, these bacteria cannot get the oxygen they need, leading to their suffocation.
Let’s take an example in soybean. For soybeans, inoculating on virgin ground is a must. Bradyrhizobium japonicum, the rhizobia species that nodulates soybeans, is not native to North American soil, and will not be present in a virgin soybean field. Adding inoculant will guarantee your soil has a high enough population to give good nodulation and ensure adequate nitrogen fixation.
If the price of inoculating your seed is worrying you, it shouldn’t. The yield increase offered by inoculating your crops is often more than enough to recoup the costs of purchasing and applying that inoculant. For example, our soybean inoculant, XiteBio SoyRhizo, has shown minimum 1-2 bushels per acre increase on average in our field trials. It only takes a 1/3 to 1/2 bushel per acre yield increase to offset the cost of inoculating, which is very feasible.
Using a liquid inoculant is another way of reducing cost. Liquid inoculants generally cost less than granular inoculants, are less bulky, easier to handle and easier to apply, ultimately saving you time and money. Liquid inoculants also easier to apply than peat-based inoculants, which are often dusty and messy during application. Buying seed that has already been treated with an on-seed inoculant is another easy way to ensure you reap the benefits of rhizobium inoculation without worrying about applying it yourself.
In summary, the benefits of rhizobial inoculation to yield and crop health are numerous and quite evident. With the cost being offset by all most all successful inoculations, this may be the cheapest insurance you can buy as your crop input.