Rotational Grazing on Land Receiving Manure Applications; Impacts of Land Management Practices on Soil and Water Quality

Rotational Grazing on Land Receiving Manure Applications; Impacts of Land Management Practices on Soil and Water Quality

Summary

We continued to conduct research on the impacts of grazing practices on soil and water quality at the USDA-ARS Bumpers Small Farm Research Station in Booneville, AR. In 2003 we installed 15 one-third acre plots with automated runoff monitoring devices. These watershed plots represent three replications each of five land-use treatments: 1) rotational grazing, 2) over-grazing, 3) hayed (not grazed), 4) over-grazing with a 50-foot buffer strip at the base of the watershed, and 5)over-grazing with a 50-foot buffer strip at the base of the watershed and planted with trees.

Between April 2004 and April 2005, seventeen runoff events occurred and were analyzed for runoff quantity, sediment load, and soluble nutrients. All plots were sampled seasonally at 0-2″, 0-4″, and 0-6″ for soil nutrients, as well as soluble phosphorus and organic carbon. Soil physical properties were analyzed twice per year using a penetrometer and bulk density assessments. Soil microbial biomass was assessed each spring using soil samples taken at 0-2″.

Soil nutrient, physical, and biological assessments were conducted on eight sets of fields, each representing fields having various intensities of grazing. We will expand our assessments by involving additional farms and farmers, representing additional soil types and grazing practices. Results from both the on-farm and on-station research will be used to develop workshops for farmers, Extension educators, and agency personnel.

Objectives/Performance Targets

• Evaluate the effects of year-round grazing management on pasture hydrology, nutrient loss associated with surface runoff, soil quality, and animal production.

  Evaluate the impact of soil and water quality parameters according to intensity of grazing practices.

  Evaluate on-farm and off-farm costs and benefits from grazing the practices under assessment.

  Collaboratively develop Water Quality Checksheets for Pastures that farmers and agricultural professionals can use to monitor soil and water quality on grazed fields.

  Use experimental results to recommend pasture management practices as modifiers in calculating the Arkansas phosphorous index.

Accomplishments/Milestones

Construction and instrumentation was completed on fifteen automated runoff plots at the USDA-ARS Bumpers Small Farm Research Station in Booneville, AR, during spring 2003. Each watershed runoff plot has an area of 0.35 acre and dimensions of 188 feet (57 m) long by 82 feet (25 m) wide. Plots are hydrologically separated by earthen berms. The base of each watershed narrows to a point where runoff water is directed to a covered 12-inch H-series fiberglass flume equipped with a pressure transducer. The transducer determines the rate and quantity of flow from storm events. A Sigma 900 max sampler, connected to the transducer, automatically collects 100 mL of sample for analysis from every 25 gallons of runoff that flows through the flume.

We collected baseline data on these plots during 2003. In April 2004, treatments were installed on the plots, with baseline assessment data used to determine treatment locations so that randomization was not confounded by natural variability. Treatments installed on these plots are:
• Hayed only
• Controlled rotational grazing without a buffer strip
• Heavy grazing without a buffer strip
• Heavy grazing with a 50-foot buffer strip where no poultry litter applications will be made
• Heavy grazing with a 50-foot butter strip as in treatment D, but with trees planted in the buffer zone and fences to exclude cattle from the buffer area

Heavy rainfall during the April 2004- April 2005 season resulted in seventeen measurable runoff events. Runoff samples were analyzed for pH, electrical conductivity (EC), total phosphorus, soluble phosphorus, total nitrogen, nitrate, ammonium, total solids, and total organic carbon.

Each watershed plot was subdivided into three sections along the gradient of the slope. Researchers collected and analyzed the following soil data from each of this plot sub-sections:
• Soil (0-6”, 0-4″, and 0-2″) nutrient analyses including pH, electrical conductivity (EC), cation exchange capacity (CEC), P, K, Ca, Mg, Na, Fe, S, Mn, Cu, and Zn
• Soil bulk density
• Water infiltration rate
• Soil compaction measured with a penetrometer
• Microbial biomass C and N (soil samples 0-2”)

Soil nutrient analyses were conducted four times per year or once during each season, while soil samples for microbial biomass were collected only in the spring. In addition to the above-mentioned soil assessments, percent forage cover over the soil surface and forage species diversity were assessed on a monthly basis. Soil and forage assessments will be statistically analyzed for bulk differences across treatments as well as for differences in plot variability.

John Pennington, a M.S. student working under Dr. Philip Moore, Jr., is primarily responsible for collecting and analyzing samples from the watersheds. His analyses will continue through September 2005. By leveraging funds from this project, Dr. Moore intends to use these plots for long-term analyses. Already, he has leveraged funds from USDA-ARS to install, fence, and fully instrument these plots.

On-farm assessments were conducted on eight sets of farms, seven in Arkansas and one in Oklahoma. Each set of farms represents a comparison of at least two different land use intensities on a given soil type. Soil data collected include 0-2″ and 0-6″ soil samples. Samples at both depths were analyzed for pH, electrical conductivity (EC), cation exchange capacity (CEC), P, K, Ca, Mg, Na, Fe, S, Mn, Cu, and Zn. Samples at 0-2″ were also analyzed for soluble phosphorus, organic carbon, and active carbon according to Weil et al. (2003). Soil physical properties analyzed were bulk density and soil surface compaction using a penetrometer.

Discussions with participating farmers about their land management practices and how these practices have changed over time have been critical for the development of this research. This information will also help guide the development of farmer and agency training sessions, to be held in the summer and fall of 2005.

Impacts and Contributions/Outcomes

Statistical analyses of data from both on-station and on-farm research is still preliminary. However, initial assessments indicate that the hayed plots have the highest concentration of phosphorus in the run-off water, but the lowest flow rate. The heavily grazed plots and the rotationally grazed plots had similar runoff during most runoff events. However, during one runoff event, the heavily grazed treatment had significantly more runoff than the rotationally grazed treatment. Across treatments, soil bulk density exhibited a significant influence on runoff volume.

Because the farm manager was unclear about the grazing protocol for the heavily grazed plots, animals were not kept on these plots continuously, but instead removed periodically. Consequently, the “heavily grazed” treatment plots were rested occasionally, but not as frequently or as regularly as the rotationally grazed treatment. This diversion from protocol resulted in some rainfall events occurring when animals were present on the rotationally grazed treatments, but not on the “heavily grazed” treatments. The event that resulted in significant differences between the rotational and heavily grazed treatments occurred when animals were grazing on both treatments.

John Pennington will use the results from the Booneville study in his thesis. He will also collaborate with Philip Moore to submit three refereed publications based on this work. The focus of these publications will be 1) Impact of grazing intensity on soil nutrient content and nutrient concentration in runoff, 2) Impact of grazing intensity on soil bulk density and quantity of runoff, and 3) Impact of grazing intensity on forage coverage and species variability. John will also present results from his work at the 2005 meeting of the Society of Soil Science and Agronomy.

During the on-farm studies, we observed limited or inconsistent differences in soil nutrients, with more soil physical properties and forage cover exhibiting clearer differences among grazing practices. During 2005, we will continue assessments on the currently identified farms, and increase the number of farm sets being analyzed to at least 20 in order to have better statistical analysis and a greater inclusion of soil types. Where possible, we will include hayed fields as a component of the set of comparisons on each farm. We will also install Plant Root Simulators (Western Ag Innovations) in selected fields to monitor surface nutrient flows among fields on each farm.

We have not conducted any on-farm meetings to date because results from analyses are still preliminary. However, we will use preliminary information to conduct initial farmer meetings during the spring and summer of 2005. These meetings will focus on the development of the pasture soil quality check-sheet. Completion of on-station and on-farm analyses by late summer will allow us to determine when we can complete the development of resource materials and conduct follow-up meetings with farmers, extension agents, and NRCS personnel.

Collaborators: