Despite extensive attention to mob grazing and its purported benefits, this study failed to find any significant difference between mob-grazed and Management Intensive Grazed (MiG) plots at any of the locations for any of the soil or forage parameters measured.
In recent years, mob grazing has gained increased attention as a management practice due to the purported benefits of improved forage yield, greater soil water retention, increased soil carbon sequestration, and range and pasture renovation. The practice involves using high stocking rates of animal pounds per acre which are moved frequently to new paddocks. The large amount of disturbance and extended rest periods that defines this practice is hypothesized to affect soil physical properties, soil biological activity, forage growth cycles and pasture species composition. Unfortunately, little quantitative research had been pursued to validate these claims when this project was proposed, although some research has been completed or started in the last few years.
Small-scale farmers in Southern Oregon have expressed increasing interest in adopting mob grazing practices. If the benefits of this practice are substantiated, then mob grazing could help to stabilize farm risk by increasing pasture resilience to extremes in rainfall and temperature and by increasing forage yields. In this way, the practice could enhance small-scale Southern Oregon farmers’ economic viability and quality of life by reducing inputs, increasing the length of the grazing season and buffering pasture systems from extreme weather events and climate change impacts.
This project worked with five producers in Jackson County to quantify the effects of mob grazing on soil organic carbon, soil water, soil biological activity, pasture yield and pasture species composition. This project was also used as a tool to educate Jackson County producers about the practice and its adaptability and benefit to local agro-ecosystems.
In Southern Oregon, innovative farmers are highly engaged in developing new systems approaches to enhancing whole farm sustainability. This project proposes to work with producers to define mob grazing and quantify the effects of such practices on overall pasture productivity. As claims of increased pasture productivity from mob grazing are attributed to improved soil health, this study will measure below-ground and above-ground parameters to test the hypothesis that mob grazing results in increased forage yields, forage species diversity and improved soil health parameters such as available water, soil organic carbon and soil biological abundance. The specific achievable objectives of this project include the following:
1. Define mob grazing based on an upper and lower limit of animal pounds per acre and a minimum recovery period to standardize regional discussions among producers and treatments implemented during this study (April 2013 ).
2. Implement grazing treatments at three locations across Southern Oregon. Two of the locations are paired farms (four total producers), with one of each pair housing management intensive grazing and mob grazing treatments, and the neighboring farm providing the control (either continuous grazing or set-stocking). The fifth farm (third location) will have management intensive grazing, mob grazing and no grazing treatments.(May 2013).
3. Collect site specific information at each of the three farms, including past management history, climate, aspect, slope, soil texture, soil pH, soil type, bulk density and baseline data for measured treatment parameters (May 2013).
4. Collect soil and forage data for three consecutive years (May 2013-October 2015). The measured parameters will include the following:
a. Total annual forage production, as measured prior to each treatment event or at the end of the season for the control treatment.
b. Pasture species richness and abundance, including weed species, measured annually in mid-summer.
c. Total soil organic carbon and nitrogen, measured annually at the end of the grazing season.
d. Annual soil biological assessment, including active and total bacteria and fungi, protozoa and nematodes.
e. Additional soil parameters – pH, bulk density and infiltration rates, measured annually at the end of the grazing season.
f. Soil moisture content, monitored throughout the growing season.
5. Statistically analyze results to determine treatment effects on forage production, forage species diversity and soil parameters, annually and over the three-year experiment (December 2015).
6. Provide site tours pre- and post- mob grazing treatment events to familiarize producers with how pastures look under this management. Combine site tours with training in use of soil quality scorecards and pasture assessment tools (July 2013, July 2015).
7. Present study results to producers regionally. Survey producers for interest in adoption of mob grazing practices (October 2013, October 2014, October 2015).
8. Develop a fact sheet summarizing the results of this study (December 2015).
Five producers in Jackson County, (Southwestern) Oregon participated in this study. The study included three separate experiments (sites), where each site had three treatments and each treatment had three replicates. All sites were on tame pasture and irrigated land.
Two producers owned adjacent property outside of Ashland, two additional producers owned adjacent property outside of Eagle Point, and a third producer was located outside of Central Point. On the paired Ashland properties, one producer practiced MiG and also had the mob treatment plots, while the neighboring property had the control plots. In this case, the control plots were located on a shipping field that experienced unpredictable grazing events and grazing pressure. All three of these treatments were grazed by cattle, and all plots were located on clay-type soils. On the paired Eagle Point properties, one producer practiced MiG and mob grazing with sheep, with the neighboring property providing the control plots. The control plots in this case were located on a field that was hayed in the spring then continuously grazed by cattle until fall. All plots were located on heavy clay soils. The Central Point producer had MiG, mob and control plots on his property. In this case, the control was complete exclusion (no grazing). All plots were located on sandy loam soils.
Prior to the beginning of the study, the producers met to discuss stocking densities and plot sizes that were manageable given the size of their farm, number of animals on hand and management availability. A minimum stocking rate of 200,000 pounds per acre was selected for the study, and a minimum rest period of 90 days was selected for the mob plots. The rotation for the MiG plots varied by season but averaged 35-45 days between grazing events.
The producers completed a survey at the beginning of the trial that collected historical management information such as general irrigation type and scheduling, type of livestock run, length of ownership, general grazing management (continuous, MiG, etc.), and fertilization history. NRCS soils data was used to generally identify soil types and help locate plots at each location on similar soils.
Each location (Ashland, Central Point, and Eagle Point) was analyzed independently from the other locations (not compared) due to differences in past and current management practices, soil types, climate variation and other factors that could not be controlled.
At the beginning of the study (May 2013), baseline data was collected for each site or plot. Tests included the quick hydrometer, CEC, Mehlich 3, pH, Walkley-Black OM, Soil infiltration, bulk density, aggregate stability, total CN, forage species and soil cover. Soil samples were also sent to the Earthfort Laboratory for analysis including total bacteria, total fungi, active bacteria and active fungi.
Throughout the course of the study, soil temperature and volumetric water content was taken at approximately 48 hours post irrigation. Plots were clipped prior to grazing of the MiG plots. Forage species and total cover as well as soil pH were analyzed at the beginning and end of each grazing season. Plot composite soil samples were sent to the USDA-ARS lab for Soil Health Tool analysis at the beginning and end of each grazing season (statistical analysis not possible due to lack of replicates).
The Oregon State University Central Analytical Lab was selected to perform the soil analyses outlined above; however, a number of difficulties followed by the closure of the lab required a change to EcoCore Analytical Services and the Colorado State University Soil, Water and Plant Testing Laboratory.
Central Point Site: There were no significant differences between treatments at this site for any of the parameters measured. Some parameters did not have sufficient replication to run statistical analysis. This site was transitioning out of an Eastern Gamagrass stand, with volunteer tall fescue, orchardgrass, white clover, perennial and annual rye and bluegrass as the predominant species.
Eagle Point Site: When considering all three treatments, significant differences were observed for copper, iron, manganese and zinc. Comparing only between mob and MiG treatments, there was a difference for copper and iron. No other significant differences were found. Some parameters did not have sufficient replication to run statistical analysis. Forage composition was predominantly tall fescue and white clover, although perennial and annual rye, meadow foxtail (not foxtail barley), and orchardgrass were other significant species.
Ashland Site: When considering all three treatments, significant differences were observed between iron and copper. When only mob and MiG treatments are considered, only differences in manganese were significant. Some parameters did not have sufficient replication to run statistical analysis. Forage varieties included tall fescue, white clover, perennial and annual rye, meadow foxtail, orchardgrass, and meadow foxtail, although velvet grass, bromes and reed canarygrass also occurred in relatively significant quantities.
Several of the parameters could not be statistically analyzed due to lack of replicates (samples were bulked) or lack of degrees of freedom. However, even in these cases, no patterns were seen in the data.
Setting statistics aside, the three producers that managed the mob and MiG plots on their land all felt that “grazing taller” (providing longer rests) was beneficial, although they felt in general that 90 days in our climate was probably too long. As a result of the study, all three of them have increased the length of rest period between grazing events on the rest of their property, with the rest period varying by season.
Study coordinators and technicians did note that on the Ashland site, there appeared to be fewer seedlings in the mob plot. This was not noted at the other two sites. This may be a result of the forage species present either providing much more shade or setting fewer seeds. It may also be the result of past management, as the Central Point site was transitioning out of an Eastern gamagrass stand while the Ashland site manager had been managing his cattle with a higher stock density and for several years.
One of the Eagle Point producers also noted that spacing between plants appears to be closer as a result of grazing taller even on paddocks not included in this study.
Coordinators and technicians also noted that although the data does not reflect a difference in infiltration rate or bulk density, as the study progressed it was far easier to insert the soil probe into the mob plots than the MiG plots on both clay sites, but especially on the heavy clays of the Eagle Point site. This was also noted by participants of the field days after only one season of mob grazing.
It is difficult to know whether mob grazing simply doesn’t provide the benefits so often reported, or whether the study design didn’t capture the differences. Some soil scientists suggest that three years is not long enough to truly cause substantial and measurable soil changes. It may also be that the parameters measured are not sensitive enough to detect these changes, or that variation in the system overwhelmed the differences due to the relatively few samples taken.
Educational & Outreach Activities
Throughout the study, the coordinators provided ongoing observations and preliminary results at workshops and classes throughout Jackson County. However, the lack of obvious differences between treatments makes it difficult to recommend the practice without significant caveats. In addition, the majority of producers at the workshops were fairly inexperienced, so mob grazing may not be an appropriate tool at this stage of their development as graziers. There was widespread interest in the study and continued conversation about the tool in classes and pasture study groups. The majority of tour and workshop attendees were small-acreage producers, although one feed store sent a representative.
This study has, however, led the producers involved to graze taller and provide longer rest periods. For example, the Central Point producer lengthened his rest periods by 10-14 days. However, he saw no advantage of a 90 day rest when compared to a 45 day rest. He felt that a 40-45 day rest, in our climate on irrigated ground, resulted in the most efficient utilization of forages when balanced with the increased labor and management associated with higher densities and quicker rotations.
The producers involved also felt that the mob plots had a significantly lower forage quality and palatability, particularly in the spring. The difference in quality was less significant in the late summer and fall.
It is hard to quantify economic benefits as a result of this study. However the producer running sheep felt that the need to provide water and shade to numerous small paddocks would increase operating costs on small operations where central water sources could not be provided in each paddock for larger numbers of animals or to several paddocks at one time for fewer animals. Shade for sheep is highly recommended in our area when daytime temperatures exceed 95° F.
On a positive note, the same operator felt that more moves require more producer time and attention being spent observing animal and soil health.
To our knowledge, few farmers have adopted this practice as a result of this study. Many of the producers most interested in this study were new farmers, and may not have the skill set to incorporate mob grazing yet. Some have discussed using it in very specific situations where rehabilitation is needed.
Areas needing additional study
The study coordinators suggest that future studies measure a narrower set of parameters over a longer period of time and with a higher stocking rate. It may also be that mob grazing shows more benefits on non-irrigated ground.