- Agronomic: general hay and forage crops
- Animal Production: grazing management
- Natural Resources/Environment: indicators
- Soil Management: soil microbiology, soil quality/health
Our 2014 trial was focused on comparing the impacts on soil health of grazing immature (before flowering) vs late maturity (after seed head formation) forages. In addition, we repeated our soil health impact on a mid-summer grazing of 2nd growth pastures and a fall/ September grazing. We had three plots in each experiment; control, (nothing done), a mechanically clipped plot, and our grazed plot and did 3 replications, all soil sampling done on day 7 post grazing. We did both Haney and PLFA soil testing on all soil samples. The only consistent finding was that on the average, the grazed plot showed lower scores on the various test results indicating soil health, Haney soil health score, Solvita CO3 levels, and PLFA total biomass.
The results were not expected and further literature reviews suggests that the soil life will respond to grazing stimulated event in 12 to 72 hours. We only tested at 7 days post grazing in 2014 and may have missed changes that occurred sooner.
This two-year-long soil health and grazing project has confirmed that in the Midwest region on diversified pastures of cool season grasses and forbs the act of grazing by sheep or cattle will stimulate an increase in microbial life in the soil as indicated by CO2 levels measured with the basal Solvita test. This increase of microbial life occurs within 12 to 48 hours of the grazing event and the production of CO2 returns to neutral or even slightly negative by 7 days post grazing.
The primary information that I can share from these on farm research findings AND our literature review is that our grazing management can make a difference in soil health. The general principals of soil health recommended to cropping programs are applicable to grazing: Limit tillage, keep the soil covered, keep living roots in the soil, and promote plant diversity. Continuous stocking with severe grazing does meet the goals of no tillage and living roots but the roots are often very short due to severe grazing, the ground is not covered with litter because it has been eaten, and over grazing often limits the number of surviving species in a pasture. Our pasture with 30 years of rotational grazing history were considered “very healthy” as evidenced by high levels of PLFA soil biomass and soil organic matter levels of 3.5% to over 5%.
The second “finding” would be that soil beneath our pasture plants is a very complicated living system. What we do with our grazing management does impact this living system and we need to utilize what we do know about “good grazing”; take half- leave half, allow adequate recovery time, maintain a diversity of plants, and more fully appreciate the value of “improved soil health”.
A third “finding” is the need to more fully understand what impacts our grazing management has on soil health resulting in future plant yields, water holding capacity, and the bottom line – grazing/pasture profitability.
Project objectives from proposal:
The goal was to compare various soil health measurements after two animal species were grazed over four different seasonal harvest periods. Or stated another way - “Does when we graze (stage of plant maturity and time of year) impact soil health in ways that can be measured?” Dr Lee Manske, North Dakota State University, teaches in his two day grazing short course on western North Dakota rangeland, that grazing 1/3 of pasture plants between the 3-leaf and flowering stage of maturity will have a beneficial impact on soil health resulting in increased fertility and increased plant growth.
My hope was to identify measurements that could demonstrate this positive soil health impact with our cool season forages on forest soils.While most of our SARE funds were used in the 2014 activities, we did have about $700 left over from unused labor funds and decided to do a trial that looked at the impacts of soil heath post grazing over time. While we had hoped to look at impacts on soil health of various grazing practices, it appears that we first need to validate a positive impact of grazing on soil health indicators.
The goals of this project, in summary, were to demonstrate that grazing immature pastures would stimulate more soil life activity than grazing mature pastures. In addition, it was hoped that we could identify the soil tests that best showed this finding.