No Till notes: 'Power of Legumes, Part 4'

Last week I visited about the results of the biological tests we ran on our winter wheat stubble, which showed very low microbial activity. The winter wheat sample had a total microbial biomass number of only 1,248.84. This low result would be expected since there is not much actively growing in the field and the residue is a high carbon-low nitrogen type residue. This high carbon-low nitrogen type residue explains why winter wheat residue is valuable in our region as the residue is hard to break down and lasts a long time. The winter wheat stubble gives our soil a good coat of armor for protection from the elements.

We also look at the results from our dry land corn field and our cover crop of milo, sunflower and a few field peas. These results were pretty much as expected, showing good levels of microbial activity and pretty good arbuscular mycorrhizal fungi levels. Total microbial biomass numbers ranged from 2,517.72 for the milo, sunflower and field pea field to 2,302.78 for the dry land corn. Both of these samples had roughly twice as much microbial activity as the winter wheat stubble.

I found the results of the next two samples very surprising. The first sample I’ll talk about is the mix of oats, radish and red clover that we planted as a forage crop following our irrigated winter wheat harvest. This sample showed a total microbial biomass rating of only 1,637.06. This number doesn’t show a whole lot more microbial activity than the winter wheat stubble. The arbuscular mycorrhizal fungi number was also low at 0.25 percent of the total microbial biomass. My understanding was that oats are very friendly for mycorrhizal fungi and I thought the number might be higher. I also understand that brassicas such as radishes are very detrimental to mycorrhizal fungi development, so maybe this explains the low number.

The numbers may also be lower than expected due to the high amount of winter wheat residues in the field. We had what I felt was poor results from the red clover in the mix. The red clover wasn’t competitive with the other crops being grown. I think we will have to find a legume that competes with the oats and radish for next year’s forage crop.

The other surprising result was the sample from the field pea stubble. The field peas had been harvested roughly five weeks prior to the day we sampled.

There was very little growing in the field. The total microbial biomass number for the field pea sample was an amazing 3,958.56. This was roughly three times higher than the winter wheat stubble and a third higher than any sample where a crop was actively growing. The arbuscular mycorrhizal fungi also made up 2.56 percent of the total biomass.

These results showed me the power of having a legume in any forage or cover crop that a grower might be considering to increase soil health and microbial activity in the field. I also think this may show the importance of having a legume in your crop rotations. I have to wonder if these test results might be an important indicator of why winter wheat seems to do well behind field peas. Our winter wheat crop was drilled into this field shortly after these samples were taken. I can’t help but think the microbial activity in the field may be a real benefit to the winter wheat crop.

I also think these results show that producers can have a real influence on their soil health with the crops we grow. Perhaps in the future we will develop a better understanding of how we can manipulate microbial populations to benefit the crops we produce. I believe we are in the infancy stage of understanding how our soil can work better for us if we are able to improve its health. Developing soil that performs better by improving the physical and functional components of the soil may lead to lower costs of production and improved yields as we develop a better understanding of the full benefits of improved soil health.