Understanding Nutrient & Sediment Loss at Breneman Farms - 6 Management Intensive Grazing and Groundwater Quality Kevan Klingberg and Dennis Frame – UW Extension/Discovery FarmsNancy Turyk - UW-Stevens Point
Breneman Farms On-farm research was conducted on the Breneman farm to investigate environmental challenges and opportunities for grass-based dairies on the Wisconsin landscape, 2002-2007. While cooperating with Discovery Farms, a UW-Stevens Point research team studied groundwater quality beneath MIG paddocks on the Breneman farm. The study objective was to explore how MIG may impact nitrogen (N) and phosphorus (P) levels in groundwater.
Breneman Farms Grazing-based dairy. 42 paddocks. 80 crossbred dairy cows + young stock. (1.6 acres / AU) Coarse textured soil Out-winter cows and older heifers Columbia County, WI
Groundwater Study at Brenemans A USDA-funded grant team studied groundwater quality beneath MIG paddocks on the Breneman farm. Brenemans were one of four farms studied Sustainable Agriculture Research and Education (SARE) project LNC01-181: “Does Management Intensive Grazing Protect Groundwater by Denitrification?” Coordinated by Nancy Turyk, UW – Stevens Point.
Groundwater Study at Brenemans Also at the Breneman farm, while the SARE groundwater monitoring equipment was in place, Turyk and colleagues investigated phosphorus in groundwater below out-wintering areas and seasonally used paddocks.
Groundwater Study at Brenemans The objective of the study was to conduct an on-farm research project over a multi-year period to explore how Management Intensive Grazing may impact nitrogen (N) and phosphorus (P) levels in groundwater by: Determining whether denitrification of nitrate N is higher in soil and groundwater under MIG paddocks compared to annually cropped fields; and Exploring the potential downward movement of P through the soil profile and into groundwater under MIG paddocks.
Groundwater Study at Brenemans These projects were conducted in the Central Sands region of Wisconsin where the depth to groundwater is shallow and soil texture is medium to coarse. The denitrification study was conducted on a total of four farms, including the Brenemans. The phosphorus study was conducted only on the Breneman farm in Columbia County.
Groundwater Study at Brenemans To conduct this study within the Breneman’s MIG paddock system: Shallow groundwater monitoring wells were installed; The upper level groundwater was analyzed for nitrite + nitrate N, ammonium N, total dissolved P, dissolved reactive P, chlorine dissolved gasses of argon, nitrogen, oxygen, nitrous oxide, methane, and carbon dioxide;
Groundwater Study at Brenemans To conduct this study within the Breneman’s MIG paddock system: Soil gas from within the root zone was analyzed to determine various concentrations and aeration conditions; Soil from beneath manure pats, urine spots and background areas was analyzed for moisture, bulk density, pH, inorganic N, and dissolved organic carbon; Soil samples were collected at sequential depths along two paddock transects , coinciding with the monitoring well locations. Soil texture was determined and soil analysis included: pH, OM, total P, Bray P, and water soluble P.
Groundwater Study at Brenemans Six groundwater monitoring wells, immediately east of stream. Source: Phosphorus in groundwater below over-wintering areas and seasonally used paddocks, N. Turyk, et al.
Nitrogen – Nitrate – Denitrification and Groundwater Reactions Nitrogen is an essential nutrient for plant and animal growth. Agricultural crop and livestock producers manage commercial fertilizer N, as well as N contained in livestock manure and rotated legume crops to ensure profitable crop production, while working to minimize losses into groundwater and surface water.
Nitrogen – Nitrate – Denitrification and Groundwater Reactions Nitrogen is a mobile nutrient. Complicated cycle of different forms, locations, transformations, and losses. Nitrate N (NO3-) is a form of N that exists unattached to soil particles within soil water. When seasons with high precipitation occur, nitrate N is subject to leaching downward, through the soil – away from plant roots, and out of the root zone.
Nitrogen – Nitrate – Denitrification and Groundwater Reactions Nitrogen cycle. Source: UW Nutrient & Pest Management Program
Nitrogen – Nitrate – Denitrification and Groundwater Reactions Natural process: water leaching through the soil Accelerated in sandy soil conditions. Downward movement of nitrate N is lost from agricultural production negatively impact crop yields. Where depth to groundwater is shallow, nitrate N can continue moving deeper through soil profile and enter groundwater. Elevated nitrate N levels in drinking water cause human and livestock health concerns.
Nitrogen – Nitrate – Denitrification and Groundwater Reactions Within the soil, certain bacteria species exist in anaerobic conditions, without oxygen. Anaerobic bacteria use nitrate N within their metabolic respiration process, ultimately converting it into N gas. Nitrogen gas moves back up through the soil profile, escaping to the atmosphere, through a process known as denitrification.
Nitrogen – Nitrate – Denitrification and Groundwater Reactions Nitrogen cycle. Source: UW Nutrient & Pest Management Program
Nitrogen – Nitrate – Denitrification and Groundwater Reactions Denitrification primarily happens in waterlogged soils after all the oxygen in soil pore spaces is forced out and replaced with water. Anaerobic bacteria responsible for denitrification typically use soil organic matter as an energy source. The possibility for denitrification to occur deeper in the soil profile and at the upper interface with groundwater, is minimized because of (typically) lower organic matter content at those depths.
Nitrogen Results This study measured and evaluated the possibility of whether nitrate N that had moved out of the root zone and into the lower levels of the soil profile and upper layer of groundwater, might be converted to N gas by way of denitrification.
Nitrogen Results Through this study, denitrification of nitrate N in groundwater was documented and measured based on the accumulation of excess N gas in groundwater. The dissolved gas composition of the shallow groundwater beneath these rotationally grazed pastures showed conditions were highly favorable for denitrification of nitrate N. Groundwater beneath these coarse textured soils, managed under a MIG system, had a large portion of nitrate N (that leached) become transformed to N gas and returned upward through the soil profile into the atmosphere.
Nitrogen Results A significant amount of dissolved organic carbon was measured in groundwater immediately beneath MIG pastures. Attributed to leaching dissolved OM from manure and urine patches. Increased dissolved organic carbon content in upper surface of groundwater beneath MIG pastures becomes the energy source for the anaerobic bacteria to denitrify nitrate N. Similar patterns were not evident in the groundwater at a corn study site (located on one of the other farms) due to the absence of a sufficient supply of dissolved organic carbon.
Nitrogen Results It was clear from comparing total nitrate N concentrations between the two farms that the NO3- content in groundwater was much lower under MIG pastures than the study site that had a conventional corn cropping system in place. These results suggest that denitrification may actively mitigate seasonal contributions of nitrate N to groundwater beneath MIG paddocks.
Phosphorus – Soil and Groundwater Reactions Phosphorus is also a naturally occurring essential nutrient for plant and animal growth. Similar to N, agricultural producers manage commercial fertilizer P, as well as the P contained in livestock manure for agricultural production while minimizing loss into surface water and groundwater.
Phosphorus – Soil and Groundwater Reactions Phosphorus is a relatively immobile soil nutrient which cycles through a complex mix of chemical and biological reactions, controlling P availability to plants and the degree to which it is held and/or immobilized within the soil. Phosphorus materials can be organic or inorganic; have various degrees of solubility in water; Practically all soluble P from commercial fertilizer or livestock manure is converted to water-insoluble P within a few hours of application when applied to non-frozen soils.
Phosphorus – Soil and Groundwater Reactions Phosphorus cycle. Source: UW Nutrient and Pest Management Program
Phosphorus – Soil and Groundwater Reactions The main environmental concern with P is that it is the limiting nutrient for algae production in surface water lakes, ponds, rivers and streams. When sufficient P is delivered to lakes, etc through surface water runoff, algae populations dramatically increase, causing aesthetic and aquatic life concerns.
Phosphorus – Soil and Groundwater Reactions There are two main ways that agricultural P can become a source of surface water pollution: Cropland erosion of soil sediment with tightly attached P; Water soluble P sources at the soil surface mixing with surface water runoff. The water soluble P sources (organic matter, livestock manure and commercial fertilizers) can mix with surface water runoff and move P downward in the landscape, away from cropland and potentially toward lakes, ponds, rivers and streams. Producers who implement soil and water conservation practices that minimize soil erosion and slow surface water runoff will help keep P out of surface waters.
Phosphorus – Soil and Groundwater Reactions Phosphorus transport from landscape to surface water and groundwater. Source: UW Nutrient and Pest Management Program
Phosphorus – Soil and Groundwater Reactions In addition to soil erosion and surface water runoff delivery mechanisms, another source of P to surface water can be through groundwater contact with lakes and streams. Groundwater as a source of P to surface water is often negligible compared to runoff inputs. Groundwater flow has been documented as a P transport mechanism to surface water: Under conditions of high water tables; On soils that have an extremely high P content; In landscapes with highly permeable sandy soils. When it occurs, groundwater P contributions to surface water are always water soluble.
Phosphorus – Soil and Groundwater Reactions In agricultural landscapes, soil test P can increase if livestock manure and/or commercial fertilizer applications are greater than the amount of P removed from the soil through crop production. Accumulation of P in the soil root zone suggests that ultimately some of the water soluble P could move deeper into the soil profile.
Phosphorus – Soil and Groundwater Reactions Most soils have profile characteristics below the root zone that strongly accept any leaching P and hold it tightly. Insoluble (iron, aluminum, manganese or calcium) phosphate precipitates form. This process may be less efficient in coarse textured soils, and the soil capacity to retain P may be exceeded, allowing small amounts of water soluble P to move deeper into the soil profile. This could become a source of P into groundwater, and thus into surface water interfaces, where soil is coarse textured and water table depths are shallow.
Phosphorus – Soil and Groundwater Reactions The project undertaken on the Breneman farm measured and evaluated the possibility of whether P moves out of the soil root zone and into the upper layer of groundwater under an MIG system on sandy soil.
Phosphorus Results Groundwater levels fluctuated seasonally and yearly to increasing precipitation, varying by 2 feet, from 6.5 to 8.5 feet deep. Dry periods resulted in lower groundwater elevations as recharge was minimal and groundwater discharge to an adjacent stream continued. Annual and seasonal dry periods also resulted in more concentrated groundwater chemistry as less dilution from recharge occurred. These responses are typical for the central sand region of Wisconsin.
Phosphorus Results The groundwater analysis showed reactive P concentrations had a median level of 0.016 mg per liter. In some wells, higher P concentrations were found during dryer precipitation times as groundwater chemistry concentrated. Several of the wells showed elevated levels of chloride and nitrate N, attributed to agricultural activity, yet those wells did not have higher P concentrations.
Phosphorus Results On this farm, soil test P (Bray) levels within the study area averaged 166 ppm in the top 6 inches, an excessively high level based on the UW–Extension soil test recommendations. Similarly, soil test P levels within the study area averaged 75 ppm in the layer 12-18 inches below the soil surface, still an excessively high level.
Phosphorus Results Phosphorus is a nutrient that can increase in the soil on MIG farms, as well as other livestock operations, due to manure applications. Although this farm has excessively high soil test P levels through the root zone, this study found that the deeper soil layers have a high affinity to grab onto and store any soluble P that may percolate that deep. Although P was measured in the groundwater below these paddocks, the study concludes that P will be retained in the soil and that P migration to groundwater is unlikely on the Breneman MIG dairy farm. This conclusion does not preclude the possibility of P contributions to surface water through overland flow of surface water runoff.
Conclusions These two projects suggest that groundwater under MIG pastures in the central sands area of Wisconsin is influenced by the MIG farming system. Ammonia N that is contained in the solid and liquid fractions of dairy cattle manure ultimately cycles and transforms to nitrate N. Nitrate N moves downward as rainfall percolates through the paddock root zone. The potential exists for this nitrate N to enter into the very top layer of the groundwater. This study shows that a significant amount of dissolved organic carbon can be present in the upper groundwater layer under MIG paddocks.
Conclusions This study suggests that the dissolved organic carbon becomes an energy source for denitrifying bacteria. Typically, at 6 to 8 feet deep, the soil profile and upper layer of groundwater will have limited carbon energy material, and anaerobic denitrifying bacteria would not be active. This conclusion that denitrification occurred is supported by measuring increased levels of N gas deep in the soil profile. This phenomenon occurred beneath the MIG paddocks and was not observed under the corn field in this study. More on-farm research should be conducted to better understand the denitrification possibility of nitrate N that reaches upper levels of groundwater under other soil types, pasture management scenarios and cropping systems.
Conclusions Phosphorus is a nutrient that can increase in the soil on MIG farms, as well as other livestock operations, due to manure applications. Although this farm has excessively high soil test P levels through the root zone, this study found that the deeper soil layers have a high affinity to grab onto and store any soluble P that may percolate that deep. Although P was measured in the groundwater below these paddocks, the study concludes that P will be retained in the soil and that P migration to groundwater is unlikely on the Breneman MIG dairy farm.
Conclusions As always, when farms are situated on landscapes with coarse textured soil and shallow groundwater, all agricultural crop and livestock systems should be carefully managed to minimize nitrate N entry into groundwater. Producers who rotationally graze livestock must still diligently manage paddocks to avoid over-application of commercial and manure nutrients. Similarly, they must manage winter stocking rates to avoid overloading the system with manure from out-wintered animals. This study confirms the importance to develop and implement nutrient management plans on grass-based MIG dairies.
Conclusions The final report for “Does Management Intensive Grazing Protect Groundwater by Denitrification?” (SARE Project LNC01-181) by N. Turyk, Dr. B. Browne, UW-Stevens Point, and Dr. M. Russelle, USDA Agricultural Research Station, St. Paul, MN can be found on the UW-Stevens Point College of Natural Resources website: http://www.uwsp.edu/cnr/watersheds/Reports_Publications/Reports/denitrification.pdf
The final report for “Phosphorus in Groundwater Below Over-wintering Areas and Seasonally Used Paddocks” by N. Turyk, P. McGinley and K. Homan, UW-Stevens Point College of Natural Resources, can be found on the UW-Discovery Farms website: http://www.uwdiscoveryfarms.org For more information about either of these studies contact: Nancy Turyk, Water Resource Scientist, Center for Watershed Science and Education, UW – Stevens Point, College of Natural Resources, Rm 216, Stevens Point, WI 54481. 715-346-4155. firstname.lastname@example.org.
Information Available This presentation is the sixth in a series of seven developed to provide the data and information collected at Breneman Farms. All of the presentations, factsheets and briefs are available on the UW - Discovery Farms website. http://www.uwdiscoveryfarms.org