How does cover cropping impact biological activity and diversity in a healthy Oklahoma soil? This was a question posed to me by James Rogers, Ph.D., my colleague and fellow principal investigator at the Noble Research Institute. At first, the answer seemed naively straightforward to me. As the number of possible host plant species increases, so should the number of soil-dwelling microbes that are capable of utilizing this new niche.
As straightforward are the question and possible answers, it turns out there are not a lot of scientific studies that have looked at the impact of cover cropping on soil microbial diversity and potential function. This likely reflects the relatively new concept of using cover crops to improve long-term soil productivity and health as well as the rapidly dropping cost associated with gene sequencing, such that precise descriptions of soil microbial communities can be made for a few thousand dollars.
James Rogers, Ph.D., leads two grazing studies at the Pasture Demonstration Farm. These projects seek to 1) evaluate winter small grain pasture production and economics when a summer cover crop is grown and 2) extend the growing season, reducing need for hay in winter.
In any case, these other studies don't describe Oklahoma soils. Geographical location is currently seen as one of the primary factors determining microbial diversity, so the results of studies done outside this region are limited in applicability. Certainly, they are good for establishing commonalities that characterize most soil types and contribute to deeper understanding and efforts to model soil microbial communities.
What is needed for my efforts is to establish knowledge based on the soils here in the southern Oklahoma and North Texas region. One of the unique resources we have at Noble – farms of our own and even those of area producers – allow us to ask questions regarding how the microbial communities in our soils work. How do fungal and bacterial communities respond to the heavy sand (and thus, low nutrient) soils at Noble's Red River Farm? What about the more acidic clay soils at our Third Street property? We are already looking at how "phytobiomes," or plants and all their associated microbes and fauna (such as nematodes), are created in these soils planted with winter wheat and switchgrass. So here I stand, given an opportunity from my colleague Dr. Rogers to ask the questions regarding phytobiome development and function using a field plot he established at our Pasture Demonstration Farm (PDF). The plot was winter cropped in wheat and either grown with a summer cover crop mix of 10 monocot and dicot species (e.g. sunn hemp, corn, millet)or not. Additionally, each of the plots was subdivided into a till or a no-till treatment, with the former predicted by me to have devastating effects on the fungal community, as fungi form web-like mycelia that help bind soil particles together. This is where the power of next-generation sequencing can help us dissect this microbial complexity and provide a pretty accurate snapshot of what is happening in an Oklahoma soil during three to four years of integrating cover crops. This chronological data is invaluable to us and our efforts to track long-term changes in our soils as climate change continues to bring us more periodic, extreme weather events. We are heavily vested in eventually directing the phytobiome to improve or maintain crop productivity and reduce our dependence on inorganic fertilizer inputs.
Members of the microbial symbiology laboratory, led by Kelly Craven, Ph.D., collect soil samples at the Pasture Demonstration Farm on Nov. 20, 1017.
We are definitely at the beginning of this question, once naively considered by me to be relatively straightforward.
Oh, and did I mention that cattle have been grazing the winter wheat component of our cover crop plots at PDF, dropping little packages of fertilizer on the ground randomly? In the future, I'll let you know how we deal with that situation. And hopefully we'll have some data analyzed to share on how a phytobiome develops for our cover crop mix/winter wheat rotation (established with tillage or with no-till) grown in 2016-2017 at PDF.