Final Report for GW15-005
Project Information
Managing a robust pasture ecosystem and optimizing available forage in sub-arctic conditions in interior Alaska is a challenge. The region is characterized by a short growing season, slow decomposition rates and undeveloped soils that are sensitive to compaction and erosion. In addition to the extreme climactic conditions, agricultural production has remained largely undeveloped due to limiting factors such as transportation challenges, high cost inputs and competition from the high yields and low prices from the continental United States. Livestock producers in Alaska use mainly unmanaged, continuous grazing practices. This has resulted in a heterogeneous pattern of pasture use; with animal feeding preferences creating patches of both over- and under-utilization, and degradation. At USDA and SARE-sponsored conferences and workshops, livestock producers have emphasized the need to develop sustainable grazing strategies that are appropriate for high latitudes and make the most of their resources.
The goal of this research was to examine the relative role of grazing mechanisms: herbivory, trampling, and dung/urine deposition on subarctic pasture productivity and ecosystem services under a simulated, intensively managed rotational grazing (IMRG) regimen. To evaluate the impacts of IMRG, a full factorial experiment of simulated trampling, muskox dung/urine deposition (muskoxen are an indigenous agricultural species), and forage clipping, mimicking IMRG timing and intensity, was conducted at the Robert G. White Large Animal Research Station, University of Alaska, Fairbanks. The treatments were applied to 96-1 m2 plots in two established pastures with different soil types over the 2014 and 2015 grazing seasons. Changes in soil biota communities and abundance
University of Alaska Cooperative Extension
Robert White Large Animal Research Station
Laura Starr's grazing research
, physical and chemical soil characteristics, plant biomass, and plant community composition were measured from one and two years of treatment applications to evaluate the potential suitability of IMRG for livestock farms in interior Alaska. Results of plant biomass showed that herbivory and manure, and the herbivory, manure, and trampling treatments have a marked impact on biomass productivity (p<0.05). In addition to increased biomass production, we observed soil responses in increased nitrogen cycling and improvement in the Haney calculation of soil health (p<0.05) after two years of manure and trampling, and herbivory, manure, and trampling treatments. This research served two purposes; to evaluate the relative roles of grazing disturbance mechanisms on sub-arctic soil and plant health and to gain insight to the plant and soil responses of IMRG regime.
Introduction
Healthy, productive pasture ecosystems are the key to providing high quality forage for raising livestock and minimizing dependence on purchased feed. Grazing is the main biotic disturbance regime on pasture ecosystems (Wang, 2006). This biotic disturbance affects plant composition, nutrient cycling, hydrological pathways, soil structure and soil biota communities of pasture ecosystems (Teague et al., 2011). Grazing pressure is heterogeneous due, in large part, to livestock preference for certain plant species, preference for new growth due to their high ratio of soluble to structural cell plant tissue, ease of access, and proximity to water (Briske et al., 2008). When livestock have unlimited access to the pasture area over the course of the growing season, as is common in continuous grazing regimes, patches of the landscape exhibit both over and under-utilization (Barnes et al., 2008).
Over-utilization and pasture degradation can result from higher than recommended grazing pressure, even if the stocking rate is conservative for the area of land available. Visible signs of these effects in the plant community are monocultures, invasive plant infestations, and/or bare ground. Soil compaction, puddling, water runoff, and erosion are indicators of pasture degradation. As plant communities, litter cover, and the soil structure change due to variable grazing disturbance, soil biota communities experience changes in available nutrients, water availability and physical habitat structure (Wang et al., 2006). Changes are ultimately feedback to impact plant production (Wang et al., 2006). The pattern of pasture over and under-utilization by livestock (or heterogeneous grazing pressure) can lead to a positive feedback loop of over grazing and degradation of pastures, even under light grazing pressure (Barnes, Malechek, Maeno, & Norton, 2008; Teague et al., 2011).
Grazing management regimes manipulate herd size, grazing area, length of grazing period, and timing of the area rotation to balance maximum forage removal and maintain ecosystem health. These practices vary from allowing unfettered access to large pasture areas over the course of years to the daily rotation of a herd in different paddocks. The grazing management regime known as intensive managed rotational grazing systems (IMRG), holistic management, or the Savory Method, proposes to mimic the short but intense grazing of wild, migratory ungulates. Wild ungulates historically grazed in vast herds across grasslands, utilizing any available forage but constantly moving due to pressures such as predation and water availability (Savory, 1983). This method is purported to increase the carrying capacity of the pasture land compared to traditionally recommended continuous grazing levels, while enhancing healthy ecosystem function (Teague et al., 2011). Intensive short duration rotational grazing models the grazing patterns of wild ungulates by stocking sections of the land at a high density and moving the herd from section to section (or paddock) at varying rates throughout the growing season, based on forage utilization and plant growth rates rather than following rigid schedules (Savory, 1983; Teague et al., 2011; Barnes et al., 2008).
Some studies such as Teague et al (2011) found that stocking rate could be maintained at the equivalent of a heavy continuous stocking rate using IRG, while maintaining ecosystem function. Other studies have reported inconclusive results (Teague et al., 2011; Barnes et al., 2008) that varied from maintaining a slightly higher stocking rate but a net financial loss due to increased labor and fencing costs, no difference between IRG and other grazing regimes, to a decrease in livestock and plant production when compared to continuous grazing (Briske et al. 2008; Barnes et al. 2008).
Grazing disturbance can be divided into three mechanisms that interact with the layer of soil associated with plant roots and soil organisms, or rhizosphere: herbivory, dung and urine deposition, and trampling. The significant spatial and temporal variability in geographic regions represent a limitation to predicting pasture ecosystem responses to grazing disturbance. Neither the relative effects nor the interaction between herbivory, dung and urine deposition, and trampling are frequently examined (Kohler, 2005; Sorensen, 2009). The ability to understand and anticipate the impact of grazing components on soil structure and soil biota communities is an important first step to understanding the role of grazing on pasture productivity and ecosystem function.
While the subarctic and arctic regions are well suited to grazing and support some of the largest herds of wild ungulates in North America, livestock production has remained largely undeveloped in Alaska (Meter, 2014). Available pasture lands are small in size compared to other states (Agriculture, 2009). This constraint of space, coupled with the extreme climate, a short growing season, and economic limitations makes efficient grazing management a matter of critical importance in the circumpolar north.
The goal of this study was to evaluate the effects and interaction of simulated herbivory, manure/urine deposition, and trampling (following IMRG methodology) on subarctic pasture responses, both above and below ground. We have documented regionally specific baseline information and begun to address some crucial knowledge gaps through the following objectives:
Determine how an intense but brief simulated grazing disturbance affects the physical and chemical components of pasture soils and plant biomass production.
- Measure changes in abundance and community structure of soil organisms, plant species composition, and amount of bare ground under the treatments.
- Evaluate the relative and interactive roles of the three grazing mechanisms: herbivory, manure/urine deposition, and trampling in sub-arctic pastures.
The project is in the final stage of analysis and manuscript preparation. Initially, the proposed research was comprised of 48 plots that were to be treated for two years. After the first year of implementation the study was expanded and 48 additional plots were added to evaluate the treatment effect after one year of implementation. This allowed us to replicate the study temporally as well as spatially. All other aspects of the study were carried out according to the methods and materials section of the research proposal. Soil samples were analyzed by Ward Laboratories using PLFA and Haney tests in the spring and fall of each year. Biomass data were collected throughout the study. Plant species composition changes and soil compaction measurements were taken in May 2014 and September 2015.
Cooperators
Research
Study Site
This research was conducted at the R. G. White Large Animal Research Station at the University of Alaska, Fairbanks, in central Alaska, USA (64.878, -147.866). The Fairbanks area has a mean annual temperature of -2.50 C and a semi-arid precipitation regime, with 27.5 cm mean annual precipitation. The area has 80 to 120 frost-free days (Mulligan et al., 2004). LARS is a 54.23 ha research farm facility that is sown with Bromis inermis (Smooth brome grass), Poa pratensis (Kentucky bluegrass), and Festuca rubra (Red fescue) and suffers persistent infestations of Hordeum jubatum (Foxtail barley). Soils at the research site are a silt loam with less than 10% clay content and poorly incorporated organic material. Historically the site has been continuously grazed by Ovibos moschatus (muskoxen) and Rangifer tarandus (reindeer) since 1980. Animals were excluded for the duration of the study.
Experimental Design
The trials were carried out over the 2014 and 2015 growing season. The experiment was replicated in two, south facing pastures with different soil types, moisture regimes, and dominant plant species. The hilltop pasture is dominated by Poa pratensis (Kentucky bluegrass) and has well-drained, Fairbanks silt loam with loess parent material. The hill bottom pasture is predominantly Bromis inermis (Smooth brome grass) and Elymus repens (Common quackgrass), and has a Minto silt loam with a colluvium and loess parent material. While both soils share similar physical and chemical characteristics, the Minto silt loam has a slightly slower drainage rate, deeper surface organic layer, and much shallower depth to the water table.
The experimental design was a full factorial combination of grazing mechanisms; simulated herbivory (H), manure and urine application (M), and trampling (T) using a randomized block design with a control plot in each block for a total of eight treatment types. The eight treatment types, MTH, MT, MH, M, TH, T, H, and control (C) were located in two pastures, (hilltop and hill bottom sites). Three blocks of eight, 1 m2 (0.5 m x 2 m) plots, were established in 2014 and treated over two years. An additional 48 plots were established in 2015 to measure the change after one year of application. The blocks were established in the pastures along east-west transects 1 m apart, with a 1 m buffer between plots. All plots were located in full sun with southern exposure. All plots were fertilized with a 10-10-10 NPK fertilizer each spring in keeping with normal pasture management.
Treatments began June 2-4, 2014, as soon as the vegetation was established and grass tillers had reached third leaf stage (Manske, 2003). Treatment applications were not scheduled events. Instead treatments were applied in response to vegetation growth. As the plants reached an average height of 20-25 cm, treatments were reapplied to simulate a grazing event. Treatment applications followed this protocol both years. Plots were left undisturbed for the remainder of the year.
Herbivory was simulated by manually cutting vegetation to an average residual height of 8-10 cm per treatment application leaving the recommended 30-50% foliage for plant recovery (Kohler et al., 2005). For the manure/urine application, fresh dung was collected from LARS muskoxen and urine was simulated by mixing 5.15 g of urea per 1 Ɩ (Persson, 2003). Designated plots received 3 l of dung and 1.5 l of urea water spread over the 1 m2 (Kohler, 2005). Trampling was simulated by rolling a 70 kg weighted tractor tire across the entire plot representing a mean pressure of 7000 kg m-2 and repeated 6 times (Kohler, 2005; Sorensen, 2009). The plot was stabbed 12 times with a shovel to mimic hoof cutting action in the soil and plant material. All sampling was conducted at the beginning and end of the experiment; June 2014 and Sept. 2015 for the two-year application and June and Sept. 2015 for the one-year application. Baseline sampling was conducted before initial treatment application. Haney Soil Health Test and PLFA analyses were conducted by Ward Laboratories, Kearney, NE.
Objective 1. Determine how an intense but brief simulated grazing disturbance affects plant biomass production and the physical and chemical components of pasture soils.
The plant biomass was collected from herbivory treatments and from all plots at the end of the growing season. Samples were dried to measure biomass production. Soil samples were collected to measure treatment effects on chemical and physical properties, to measure soil respiration (Solvita® CO2 burst test), organic matter content, soluble soil nutrient content, soluble organic C:N ratios, and soil health calculation using a Haney Soil Health Test. Each plot sample consisted of 6 – 15 cm deep soil cores which were pooled and frozen within 4 hours.
Changes to the soil bulk density and penetration resistance were calculated as a measure of soil compaction before and after the study. Bulk density was measured using a bulk density soil core sampler to remove one core per plot. Penetration resistance was measured using an Eijkelkamp hand penetrometer. The device was inserted to a depth of 15 cm four times per plot to obtain a mean measurement of the pressure required (resistance) to insert the cone and rod into the soil (Duiker, 2002).
Objective 2. Measure changes in abundance and community structure of soil organisms and plant species composition under the treatments.
Microbial biomass and community changes were analyzed using a phospholipid fatty acid analysis (PLFA). This analysis was conducted using the same core samples that were collected for the Haney test. The plant species composition was conducted at the beginning and end of the study using a m2 frame and determining the proportion of area covered by that each species as well as the amount of bare ground.
Objective 3. Evaluate the relative and interactive roles of the three grazing mechanisms: herbivory, manure/urine deposition, and trampling in sub-arctic pastures.
The effects of the treatments on the soil chemical, biological, and physical properties were analyzed using Sigma Plot 13.0 software. The data were analyzed as four separate groups, hilltop – one year treatment, hilltop – two year treatment, hill bottom – one year treatment, and hill bottom – two year treatment. From the assays, the mean was calculated for each of the eight treatment types from the three replicate blocks in the group. These values were used to conduct the one way analysis of variance (ANOVA).
Pretreatment data analysis indicate no initial differences between plots in any of the metrics within each site. Post-treatment analysis revealed a significant effect of grazing components on biomass production and several soil chemical parameters across locations and treatment duration. The MTH and MH treatments had a positive effect on biomass production (p<0.05) over control and H in the two-year hilltop treatment. The T and TH treatments had an adverse effect on biomass production across all sites and years. The H and TH treatments had a negative impact on the percentage of bare ground across all groups. While we anticipated H to have an increased yield over the control plots due to the frequent clippings, this was not the case, despite the inorganic fertilizer applications. The plant species composition is currently being analyzed.
The MT and MTH treatments had a positive impact on total H2O soluble nitrogen and inorganic nitrogen over the control, T and H treatments after two years of treatment in both sites. This trend was evident at both sites (p<0.1) after 1 year of treatment. The treatments MT and MTH had the most positive effect after two years of treatment, consistent on both sites. In addition to the nitrogen analyses, at the 2 year - hilltop site, there were significant improvements in the amount of H3A extracted organic phosphorus, calcium, and iron in plots treated with MTH and MT. The soil health calculation, an index that combines several properties that contribute to the biological well-being of the soil (Haney, 2012) ((solvita CO2/organic C:N)+(water extractable organic C/100)+(water extractable organic N/10)), found that MT and MTH treatments had a positive impact over the control, T, and H treatments in the 2 year – hilltop site while the 1 year – hilltop site saw an improvement of M treatment over the control. In the hill bottom site, the soil health calculation detected no difference in the two-year treatment, and a positive impact on the one-year treatment site of MT over M applications. While no significant changes in soil respiration and organic C:N were detected, a treatment effect approached significance in 3 of the 4 groups (p<0.1).
In every case where a significant difference was detected, MT treatments had the greatest positive impact on soil chemical parameters followed by MTH, suggesting that the mechanical incorporation of manure plays an important role in nutrient cycling in the sub-arctic soils at the experimental site. We were unable to detect a change in soil compaction due to treatment, with neither changes in bulk density or soil penetration resistance. This may be attributed to the brevity of the experiment or the generally compacted conditions of the sites at the beginning of the study.
The PLFA analyses detected a change in arbuscular myccorhizal biomass in the 2 year - hill bottom pasture only. This biomass change was in response to MT when compared to H treatments. The 1 year – hilltop pasture, while not significant (p=0.08), demonstrated a trend towards increased % of arbuscular myccorhizal fungi. No other change in microbial species biomass or community composition was detected.
The positive impact of the simulated MTH treatment on both plant and soil chemical parameters in only 2 years indicates that grazing can be used as a tool to impact pasture productivity and remediate degraded sub-arctic pasture soils in the region.
This study was limited by the short time frame. Often it takes several years in a subarctic climate to see the full effects of any management changes. In addition to the time frame, the largest impediment to the study was that lack of complexity inherent in a live grazing system. Correct trampling pressure was difficult to estimate and implement for the simulation. We were not able to address the spatial heterogeneity of animal grazing which would ultimately determine the positive or detrimental impact of any grazing system.
Research Outcomes
Education and Outreach
Participation Summary:
Outreach efforts took place throughout the study. The events that occurred in the summer 2015 through spring 2016 included groups from student, producer, and academics in local, national, and international venues. In August 2015, we had an open house in conjunction with the Soil and Water Conservation District at the research site to discuss the grazing project and SARE-funded research that the Soil and Water Conservation District was conducting. During the month of September, I created a science lab based on my research. I conducted two field days with a 4th grade class at a local elementary school to complete the lab and discuss the research and results. The lab was left with the teacher who plans to continue the activity in future years.
In November 2015, I attended the XXIII International Grassland Congress, Delhi, India and presented a poster. This provided the opportunity to discuss my research in a global context where circumpolar agricultural issues are typically underrepresented.
At the University of Alaska, Fairbanks, I presented my research to undergraduate students in the Sustainable Agriculture class. I gave a formal presentation of the research at the 2016 Society for Range Management Annual Meeting in Corpus Christi, TX and was afforded many opportunities to discuss the project with attendees.
I am scheduled to share my findings at a workshop at the 2017 Alaska Sustainable Agriculture Conference in Fairbanks, AK. This particular education and outreach effort is targeted at providing community stakeholders with practical information from the research project and the associated impacts specifically for interior of Alaska. It is my goal to improve the understanding of the impacts associated with managed grazing on the sub-arctic plants and soil to help producers make informed decisions on grazing management strategies that reduce costly imported inputs and improve economic returns, and promote sustainable agriculture in Alaska.
One manuscript, Farming muskoxen for qiviut in Alaska: A feasibility study, authors Laura Starr, Joshua Greenberg, and Janice Rowell, has been accepted for publication by the journal Arctic and is due to be published in March 2017. The manuscript, Sustainable livestock production on the frontier: Plant and soil responses to simulated managed grazing in subarctic Alaska, is being prepared and will be submitted to the journal Rangeland Ecology & Management for publication.