Rotational Grazing on Land Receiving Manure Applications; Impacts of Land Management Practices on Soil and Water Quality
We initiated research on the impacts of continuous and rotational grazing practices on soil and water quality by collecting baseline data from on-farm and on-station research sites. At the USDA-ARS Bumpers Small Farm Research Station in Booneville, AR, fifteen automated runoff plots were installed and baseline soil and runoff data were collected from these plots. We will use this baseline data to randomize plots prior to installing treatments in spring 2004.
Soil nutrient, physical, and biological assessments were conducted on six farm fields, representing one continuously grazed and one rotationally grazed field on each of three soil types. We will expand our assessments by involving additional farms and farmers, representing additional soil types and grazing management practices. Results from both the on-farm and on-station research will be used to develop workshops for farmers, Extension educators, and agency personnel.
We continued 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 fifteen watershed plots with automated runoff analyzers. Between April 2004 and April 2005, seventeen runoff events ocurred and were analyzed for volume of runoff, sediment load, and nutrients in the sediment and runoff water. Each spring since 2002, soil samples were taken at 0-2″, 0-4″ and 0-6″ and analyzed for soil nutrients, soluble phosphorus, and organic carbon. Sterile samples taken at 0-2″ were analyzed for microbial nitrogen and phosphorus. Soil physical assessments, consisting of penetrometer and bulk density analyses were made in both the spring and fall. Forage biomass was measured throughout the year.
Soil nutrient, physical, and biological assessments were conducted on eight sets of farm fields, representing different grazing intensities. In 2005, we will expand our assessments by involving additional farms and farmers, representing additional soil types and grazing management practices. Results from both the on-farm and on-station research will be used to develop workshops for farmers, Extension educators, and agency personnel.
- Evaluate the effects of year-round grazing managemtn 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 grazing intensity.
Evalute on-farm and off-farm costs and benfits from grazing practices under assessment.
Collaboratively develop Water Quality Checksheets for Pastures, which 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.
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) 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. These runoff samples are analyzed for pH, electrical conductivity (EC), total phosphorus, soluble phosphorus, total nitrogen, nitrate, ammonium, total solids, and total organic carbon.
Treatments were not installed on plots immediately following construction. Instead, the first year following construction was used to collect baseline data and identify natural variability among the plots. Unfortunately, low rainfall during 2003 resulted in only four measurable runoff events. We are hoping to have at least two more runoff events during the spring of 2004 prior to randomizing the plots and installing research treatments. Treatments to be installed on these plots are:
• Hayed only
• Continuously heavy grazing.
• Controlled rotational grazing without a buffer strip
• Controlled rotational grazing with a 50 foot buffer strip where poultry litter applications will be omitted
• Controlled rotational 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
Besides runoff, researchers collected and analyzed the following baseline data:
• Soil (0-6”) 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”)
We will collect another set of baseline analyses prior to initiating treatments on the watershed plots. Following initiation of treatments, soil analyses will be conducted four times per year or once during each season. In addition to the above-mentioned soil assessments, percent forage cover over the soil surface and forage species diversity will be 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., will be primarily responsible for collecting and analyzing samples from the watershed. His analyses will continue through December 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 four farms, two in Arkansas and two in Oklahoma. These farms represent three paired comparisons of rotational and continuous grazing, each pair being on a different soil type. Soil data collected was similar to the on-station experiments, except that microbial biomass was not analyzed.
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 fall of 2004 and 2005.
In addition to the on-farm and on-station assessments outlined in the project proposal, we collected and analyzed soil samples at the conclusion of a three-year rotational and continuous grazing comparison study that was conducted by Dr. Kimberly Cassida at the University of Arkansas Research Farm in Hope, AR. Study results indicated that while grazing systems and stocking rates did have a significant effect on cattle weight gain, amounts of hay removed from pastures, and amounts of supplemental hay fed to cattle, the effects on soil quality parameters were inconsistent. There were few differences between rotational and continuous grazing practices in regard to soil chemical, biological or physical parameters when soil measurements were averaged across plots. Further statistical analyses will be conducted on this data to determine whether differences in variability exist across treatments.
Impacts and Contributions/Outcomes
To date, assessments have focused on gathering baseline data. For on-farm studies, we have observed limited or inconsistent differences when data from rotational and continuously grazed fields are averaged across fields. However, continuously grazed fields tend to show greater variability within paddocks as compared to rotationally grazed fields. This variability is related to more pronounced congregation areas and paths in the continuously grazed paddocks compared to those being rotationally grazed. Based on this preliminary information, we will identify additional farm pairs for assessment and concentrate our analyses on differences in the variability of soil parameters between continuous and rotationally grazed paddocks. We will also conduct assessments of soil cover and vegetation type similar to those being conducted for the on-station research. Finally, we will install Plant Root Simulators (Western Ag Innovations) in selected fields to monitor differences in surface and subsurface nutrient flows between paired fields.
Results from the Hope Research Farm study were presented, as a poster, by University of Arkansas Assistant Professor Dr. Mary Savin and her graduate student Peter Tomlinson at the annual Soil Science Society of America Meetings in 2003. Co-authors of this poster were Barbara Bellows and Kimberly Cassida.
We have not presented any other results to date since our information is preliminary. We will initiate development of educational materials this summer and conduct farmer, Extension, and agency trainings in the fall of 2004 and 2005.
As we conduct the on-farm experiments and identify additional farms and farmers to engage in this study, we will continue to involve farmer participants in the research process as sources of management information, to help guide the development of educational materials and to provide feedback on proposed phosphorous index guidelines.
USDA-ARS Soil Scientist
Plant Science 115
Fayetteville, AR 72701
Office Phone: 4795755724