Tag: manure impacts

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Environmental Benefits of Manure Application

For centuries, animal manure has been recognized as a soil “builder” because of its contributions to improving soil quality. Environmental benefits are possible from manure application if manure and manure nutrients are applied and timing and placement follows best management practices. When compared to more conventional fertilizer, manure properly applied to land has the potential to provide environmental benefits including:

    • Increased soil carbon and reduced atmospheric carbon levels
    • Reduced soil erosion and runoff
    • Reduced nitrate leaching
    • Reduced energy demands for natural gas-intensive nitrogen(N) fertilizers

Manure Effects on Soil Organic Matter

Manure contains most elements required for plant growth including N, P, potassium, and micronutrients (Manure as a Source of Crop Nutrients and Soil Amendment). However, it is manure’s organic carbon that provides its potential environmental value. Soil organic matter is considered nature’s signature of a productive soil. Organic carbon from manure provides the energy source for the active, healthy soil microbial environment that both stabilizes nutrient sources and makes those nutrients available to crops.

photo of solid manure spreader
Manure is comparable to commercial fertilizer as a plant food and, if applied according to a sound nutrient plan, has environmental benefits over commercial fertilizer. cc2.5 manure nutrient management group

Several long-term manure application studies have illustrated its ability to slow or reverse declining soil organic levels of cropland:

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    The ability of manure to maintain or build soil organic matter levels has a direct impact on enhancing the amount of carbon sequestration in cropped soils.Manure organic matter contributes to improved soil structure, resulting in improved water infiltration and greater water-holding capacity leading to decreased crop water stress, soil erosion, and increased nutrient retention. An extensive literature review of historical soil conservation experiment station data from 70 plot years at 7 locations around the United States suggested that manure produced substantial reductions in soil erosion (13%-77%) and runoff (1%-68%). Increased manure application rates produced greater reductions in soil erosion and runoff. Additional studies during years following manure application suggest a residual benefit of past manure application.

    Overview of Manure Impacts on Soil (Mark Risse, University of Georgia). Visit the archived webinar for additional videos on carbon, fertility, and soil health.

    Manure Effects on Soil Erosion

    In addition, surface application of manure behaves similarly to crop residue. Crop residue significantly decreases soil erosion by reducing raindrop impact which detaches soil particles and allows them to move offsite with water runoff. Data has been published showing how manure can coat the soil surface and reduce raindrop impact in the same way as crop residue. Therefore, in the short-term, surface manure applications have the ability to decrease soil erosion leading to a positive impact on environmental protection.

    Organic Nitrogen

    In addition, organic N (manure N tied to organic compounds) is more stable than N applied as commercial fertilizer. A significant fraction of manure N is stored in an organic form that is slowly released as soils warm and as crops require N. Commercial fertilizer N is applied as either nitrate or an ammonium (easily converted to nitrate). Nitrate-N is soluble in water and mobile. These forms contribute to leaching during excess precipitation (e.g., spring rains prior to or early in growing season) or irrigation. Manure N’s slow transformation to nitrate is better timed to crop N needs, resulting in less leaching potential. In fact, manure N is a natural slow-release form of N.

    Energy Benefits

    Recycling of manure nutrients in a cropping system as opposed to manufacturing or mining of a new nutrient resource also provides energy benefits. Commercial nitrogen fertilizers consume significant energy as a feedstock and for processing resulting in greenhouse gas emissions. Anhydrous ammonia requires the equivalent of 3300 cubic feet of natural gas to supply the nitrogen requirements of an acre of corn (assuming 200 lb of N application). Phosphorus and potassium fertilizers also have energy requirements for mining and processing. Substituting manure for commercial fertilizers significantly reduces crop production energy costs

    It is important to remember that the environmental benefits of manure outlined in this article are only beneficial when best management practices for reducing soil erosion are implemented in concert with proper levels of manure nutrient application and use.

    Recommended Reading on Environmental Benefits of Manure

     

  • Authors: Rick Koelsch, University of Nebraska, and Ron Wiederholt, North Dakota State University
  • Reviewers: Charles Wortmann, University of Nebraska, and Steve Brinkman, Iowa NRCS
    Last reviewed on October 25, 2022 by Leslie Johnson, Animal Manure Management Extension Educator, Nebraska Extension.
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Preferential Flow of Manure in Tile Drainage

Guidelines for Applying Liquid Animal Manure to Cropland with Subsurface and Surface Drains

Liquid animal manure is a valuable source of nutrients and organic matter for crop production and may be applied by a variety of methods including spray irrigation,land surface spreading, and shallow subsurface injection. Because of relatively low nutrient concentration, liquid animal manure may be applied at relatively high volumes, but it is generally recommended that it not be applied at rates that exceed the soil infiltration rate, nor exceed the amount needed to bring the soil to field water holding capacity (Johnson and Eckert, 1995). Even when similar guidelines are followed, liquid manure discharges from agricultural drains has been reported in soils with subsurface drainage due to macropore flow (Geohring et al., 2001). | Related: Manure & Nutrient Management in Tile Drained Lands…

Figure 1. Liquid effluent contaminating surface water. (Photo courtesy of Rick Wilson, OEPA)

Application of liquid animal manures to soils with subsurface drainage has been linked to contamination of the effluent with nutrients (Cook and Baker, 2001; Geohring et al., 2001), particulate organic matter (Barkle et al., 1999), estrogens (Burnison et al., 2003), bacteria (Bicudo and Goyal, 2003; Cook and Baker, 2001; Dean and Foran, 1992; Jamieson et al., 2002; Joy et al., 1998),and antibiotics (Kay et al., 2004). These findings are not universal, however, as liquid animal manures can be applied without any detectable adverse effects on water quality. For instance, Randall et al. (2000) noted no difference in nitrogen, phosphorus, or fecal indicator bacteria losses in drainage effluent when comparing plots fertilized with liquid dairy manure and mineral fertilizer.

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Role of Drainage Depth and Intensity on Nutrient Loss

The fact that liquid animal manure nutrients can be safely land recycled in some instances, but are discharged in subsurface drainage water under different circumstances, suggests a complex system that needs to be managed. Soil texture, available water holding capacity, tillage history, as well as the type and quantity of manure applied, application method, and timeliness of rainfall after application may all play a role in determining the fate of the manure.

Liquid Manure Applied to Subsurface-Drained Cropland

The available water holding capacity of the upper 8 inches of the soil provides an estimate of the maximum volume of water that can be applied before additional water, manure, and nutrients may begin to move through the soil profile (refer to Table 1). Manure application rates may need to be adjusted the day of application to avoid reaching the available water holding capacity of the soil and is one factor determining the maximum volume that should be applied. Application rates should not exceed the lower of the nutrient restriction, available holding capacity of the soil or 13,000 gallon/acre. Smaller multiple low applications allow the soil to absorb liquid animal manures better than one large application.

Table 1. Available Water Capacity (AWC) Practical Soil Moisture Interpretations for Various Soils Textures and Conditions to Determine Liquid Waste Volume Applications not to exceed AWC.

Suggestions To Minimize the Downward Movement of Liquid Manure

Have an Emergency Plan

Identify subsurface drain outlets, and control or regulate discharge prior to application, or have on-site means of stopping the discharge from subsurface drains. Subsurface drainage outlets should be monitored before, during, and after application for potential liquid manure discharge. Drainage control structures and inline tile stops are recommended control practices to reduce the risk of a discharge, while tile plugs may be used in emergency situations but have been known to fail (Hoorman, 2004). Use caution not to back-up water where it may impair the functioning of an adjacent subsurface drainage system. Develop a contingency plan to handle situations when liquid manure discharges to ditches or streams.

Select Low-Risk Areas

Figure 2. Control structures and tile stops reduce surface water contamination if properly installed. (Image courtesy of Agri-Drain, Adair, IA)

Liquid manure should not to be applied on soils that are prone to flooding, as defined by the National Cooperative Soil Survey (or in the Flooding Frequency Soil List posted in Section II eFOTG), during the period when flooding is expected. Manure can be applied if incorporated immediately or injected below the soil surface during periods when flooding is not expected.

Watch the Weather (Past and Future)

Avoid applying manure when rainfall is predicted, eminent, or directly after a rainfall event. After a significant rainfall event, the site should be allowed to drain to below field capacity, so that the soil has the capacity to absorb additional water or liquid animal manure. As part of the manure application record keeping, maintain a log of weather forecasts and actual weather conditions 24 hours before and after a manure application event.

Figure 3.Field prone to flooding. (Photo courtesy of Norm Widman, NRCS)

Keep Drains Well-Maintained

Repair broken drains and blowholes prior to application, and follow recommended/required minimum setback requirements (setback distances vary from state to state) for surface inlets. See fact sheet on Liquid Manure Application Rates for Subsurface and Surface Drained Cropland in “Related Publications” section.

Are Drains Flowing?

Figure 4. Avoid applying liquid animal wastes to saturated soils. (Photo courtesy of Rick Wilson, OEPA)

Liquid manure should not be applied to subsurface drained cropland if the drains are flowing. Generally, flowing subsurface drain indicate soil moisture levels that are near or exceeding the soil water holding capacity. The addition of liquid manure under these conditions will increase the probability of manure moving downward and discharging through these drains or moving overland as surface runoff.

Consider Concentration of Application

Application rates should be closely tied to nutrient requirements and available holding capacity of the soil. The method of application can influence application rates. For example, with an injection toolbar with four nozzles on 30-inch spacing, each knife and nozzle produces a concentrated application to a small area. Under these concentrated flow conditions, the effective rate differs considerably from an average application rate. The effective rate is calculated as the volume of manure applied per unit area per nozzle. For example, assume a 10,000 gallon/acre application rate, an injection toolbar with 30-inch spacing and 6-inch sweeps, the effective rate is 50,000 gallon/acre, five times greater than a uniform even distribution over an acre.

Avoid Ponding

Liquid manure should be applied in a manner that will not result in ponding, or runoff to adjacent property, drainage ditches, or surface water regardless of crop nutrient need; and should be uniformly applied at a known rate. Liquid animal manure applications using irrigation or surface application equipment tend to have a greater risk of ponding.

Consider Tillage

Fields with a history of downward movement of manure and/or bare/crusted soils may require some tillage to improve infiltration and absorption of the applied liquid. Prior to manure application, use shallow tillage to disrupt the continuity of worm holes, macropores and root channels (preferential pathways) to reduce the risk of manure reaching drain lines, or till the surface of the soil 3 to 5 inches deep to a condition that will enhance absorption of the volume of liquid manure being applied. This is especially important if shallow drains are present (< 2 feet deep). Any pre-application tillage should leave as much residue as possible on the soil surface to minimize soil erosion.

Clay Soil Considerations

Figure 5. A Paulding clay soil with high shrink swell capacity may need to be tilled before application, and/or smaller initial liquid applications to help close the cracks. (Photo courtesy of Jim Lopshire, The Ohio State University).

Clay soils with a high shrink swell capacity tend to have larger deeper cracks during dry conditions. These soils may require tillage to disrupt the cracks and macropores, and a lower initial application rate applied to the soil to help close the cracks. Cover crops may be planted to improve soil structure and absorb available manure nutrients. Determine the most limiting application rate based on the field conditions and nutrient limitations (may vary from state to state).

Depth of Injection

Figure 6. For the most effective application,liquid manure should be applied shallow and uniformly into the soil surface. (Photo courtesy of Jon Rausch, The Ohio State University).

Shallow injection is recommended for liquid manure. Till the soil at least three inches below the depth of injection prior to application, and/or control outflow from all drain outlets prior, during, and after manure application.

Perennial Crop and No-Till Precautions

For perennial crops (hay or pasture) or continuous no-till fields where tillage is not recommended, all subsurface drain outlets from the application area should be monitored, and if manure laden flow should occur, all effluent should be captured. Crops with deep tap root systems (alfalfa) tend to have more problems than hay crops with fibrous roots (grass) because liquid animal manures may flow along the tap roots to subsurface drains and outlet to surface water.

These criteria may be waived if the producer can verify there is no prior history of manure discharge via subsurface drains, or if a system is in place to capture the discharge. However, if there is a discharge, the producer is liable for damages and is subject to being classified as a Concentrated Animal Feeding Operation (CAFO).

Liquid Manure Applied to Systematic Surface Drained Fields

Fields or areas of fields that have systematic “surface drainage” systems e.g., shallow surface drains spaced 100 to 200 feet apart—NRCS Surface Drainage-Field Ditch Practice Standard 607) are considered concentrated flow areas. However, if special precautions are taken, manure can be applied in the surface drains with minimal risk of surface runoff. This does not apply to the collector surface drains (mains, ditches, etc.) or drains bordering the fields.

Figure 7. Till the soil 3 to 5 inches deep or 3 inches below the depth of injection to disrupt macropores. (Photo courtesy of Jon Rausch, The Ohio State University).

The following special manure application techniques shall be used:

  1. Till the soil surface at least 3 to 5 inches deep prior to liquid manure surface application. Pre-till within 7 days of application.
  2. Surface-apply liquid manure uniformly over the entire soil surface on the freshly tilled soil (3 to 5 inches) to allow the liquid manure to be absorbed into the soil surface.
  3. For fields with no subsurface drainage, liquid manure can be injected directly without prior tillage. If subsurface drainage is present as well as surface drains, then the above recommendations for subsurface drained cropland apply as well.

d. Manure application rates should be adjusted to consider the most limiting factor and include the ability of the soil to accept, store and hold liquid manure, water, and nutrients.

Follow recommended/required setbacks from environmentally sensitive areas for surface inlets. See fact sheet on Liquid Manure Application Rates for Subsurface and Surface Drained Cropland.

Summary

Improved management is a key issue in greatly reducing the potential of liquid manure reaching our surface water. While climate and some environmental conditions cannot be controlled, producers can better manage and control when and how they apply liquid manure. These recommended practices are intended to help producers apply liquid manure in a manner that minimizes the potential to impact water resources through the downward movement of manure into subsurface (tile) drains. These recommendations incorporate the best available knowledge.

Acknowledgments

The authors acknowledge Dr. Harold Keener, The Ohio State University; Dr. Timothy H. Harrigan and Dr. William G. Bickert, Michigan State University; Michael J. Monnin and Frank E. Gibbs, Ohio Natural Resources Conservation Service, and Susanne R. Reamer and Michael I. Gangwar, Michigan Natural Resources Conservation Service, team members who helped organize and conduct the “Liquid Animal Manure Application on Drained Cropland: Preferential Flow Issues and Concerns Workshop” and reviewed the regional guidelines. The workshop was organized and sponsored by The Ohio State University, Michigan State University, and cooperating organizations, with partial support from the USDA–CSREES Great Lakes Regional Water Quality Program, USDA–Natural Resources Conservation Service, Ohio Compost and Manure Management, Ohio State University Extension, Great Lakes Basin: Soil Erosion and Sediment Control, and the Overholt Drainage Education and Research Program.

References

  • Barkle, G.F., T.N. Brown, and D.J. Painter. 1999. Leaching of particulate organic carbon from land-applied dairy farm effluent. Soil Science 164 (4): 252–263.
  • Bicudo, J.R., and S.M. Goyal. 2003. Pathogens and manure management systems: A review. Environmental Technology 24 (1): 115–130.
  • Burnison, B.K., A. Hartmann, A. Lister, M.R. Servos, T. Ternes, and G. Van Der Kraak. 2003. A toxicity identification evaluation approach to studying strogenic substances in hog manure and agricultural runoff. Environmental Toxicology and Chemistry 22 (10): 2243–2250.
  • Cook, M.J., and J.L. Baker. 2001. Bacteria and nutrient transport to tile lines shortly after application of large volumes of liquid swine manure. Transactions of the American Society of Agricultural Engineers 44 (3):495–503.
  • Dean, D.M., and M.E. Foran. 1992. The effect of farm liquid waste application on tile drainage. Journal of Soil and Water Conservation 47 (5): 368–369. *Geohring, L.D., O.V. McHugh, M.T. Walter, T.S. Steenhuis, M.S. Akhtar, and M.F. Walter. 2001. Phosphorus transport into subsurface drains by macropores after manure applications: Implications for best manure management practices. Soil Science 166 (12):
  • Hoorman, J.J. 2004. Ohio liquid manure violation water quality data, Ohio Journal of Science, Vol. 104, No. 1, A-34.
  • Hoorman, J.J., J.N. Rausch, T.M. Harrigan, W.G. Bickert, M.J. Shipitalo, J.R. Reamer, F.E. Gibbs, M.J. Gangwar, and L.C. Brown. 2005. Summary of education and research priorities for liquid manure application to drained cropland: preferential flow issues and concerns, ASAE Meeting, Paper No: 52062. Tampa Bay, FL.
  • Jamieson, R.C., R.J. Gordon, K.E. Sharples, G.W. Stratton, and A. Madani. 2002. Movement and persistence of fecal bacteria in agricultural soils and subsurface drainage water: A review. Canadian Biosystems Engineering 44: 1.1–1.9.
  • Johnson, J., and D. Eckert. 1995. Best management practices: Land application of animal manure. Ohio State University Extension Publication AGF-208-95 Available online at http://ohioline.osu.edu/agf-fact/0208.html (Verified 8 September 2004).
  • Joy, D.M., H. Lee, C.M. Reaume, H.R. Whiteley, and S. Zelin. 1998. Microbial contamination of subsurface tile drainage water from field applications of liquid manure. Canadian Agricultural Engineering 40 (3):153–160.
  • Kay, P., P.A. Blackwell, and A.B.A. Boxall. 2004. Fate of veterinary antibiotics in a macroporous tile drained clay soil. Environmental Toxicology and Chemistry 23 (5): 1136–1144.
  • Randall, G.W., T.K. Iragavarapu, and M.A. Schmitt. 2000. Nutrient losses in subsurface drainage water from dairy manure and urea applied for corn. Journal of Environmental Quality 29 (4): 1244–1252.
  • Rausch, J.N., J.J. Hoorman, T.M. Harrigan, W.G. Bickert, M.J. Shipitalo, J.R. Reamer, F.E. Gibbs, M.J. Gangwar, and L.C. Brown. 2005. Guidelines for liquid manure application on drained cropland, ASAE Meeting, Paper No: 52061. Tampa Bay, FL.

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Copper Sulfate Foot Baths on Dairies and Crop Toxicities

Environmental Issues for Land Applying Copper Sulfate

A rising concern with the application of dairy wastes to agricultural fields is the accumulation of copper (Cu) in the soil. Copper sulfate (CuSO4) from cattle footbaths is washed out of dairy barns and into wastewater lagoons. The addition of CuSO4 baths can increase Cu concentration significantly in manure slurry, from approximately 5.0 grams per 1,000 liters to 90.0 grams per 1,000 liters. The Cu-enriched dairy waste is then applied to agricultural crops, thus raising concerns about how soils and plants are impacted by these Cu additions.

Once added to the soil, the Cu+2 from CuSO4 can:

  1. remain in the soluble form of Cu+2 which is available to plants;
  2. adsorb to organic matter;
  3. adsorb to clay particles; or
  4. be converted to less available mineral forms.

Typically, the majority of Cu strongly adsorbs to soil organic matter and clay surfaces. In fact, Cu binds to organic matter more strongly than any other micronutrient. Dairy manure is rich in organic matter and will naturally have greater Cu adsorption than dairy lagoon water which is low in organic matter. In soils with pH values greater than 7.0, soluble Cu+2 will react with water to form either Cu(OH)2 or associations with Fe-oxides. Thus, almost all Cu added to soil typically stays in soil. For more information regarding soil Cu reactions, read Copper Deficiency in Cereal Grains.

The potential for groundwater contamination, via enhance downward Cu transport, will be greater in sandy, acidic soils or under irrigated conditions. And although increasing soil organic matter content will increase Cu adsorption, Cu associated with dissolved organic phases could also be transported downward. However, most studies suggest that soluble Cu transported through soils does not exceed the national drinking water standard of 1.3 mg/L. For more information regarding Cu transport, read Kinetics of copper desorption from soils as affected by different organic ligands.

Research Findings for Land Applying Copper Sulfate

With the strong binding of soluble Cu to soils, very little of the applied Cu is plant-available. Overall, the potential for Cu toxicities in plants is relatively small given the amount of Cu that is added through dairy-waste application. Preliminary results from the USDA–ARS in Kimberly, Idaho, showed that extractable soil Cu concentrations ranging from 1 to 154 parts per million (ppm) in a calcareous soil had no effect on alfalfa or corn silage biomass yields, while plant survival was drastically impeded at concentrations greater than 323 ppm.

Copper application rates used in this study to achieve reductions in yields and plant survival greatly exceeded rates typically seen for dairy manure applications. In a similar study in New York, Flis et al. (J. Animal Science, 2006, 84:184-185, supplement 1) applied CuSO4 at 0, 6.3 and 12.6 pounds Cu per acre to corn silage, orchardgrass, and timothy grass using Cu rates equivalent to those typical to dairy waste applications. Corresponding soil Cu concentrations were 11, 13 and 18 ppm, respectively. The varying Cu application rates had no effect on grass or corn silage yields, although tillering and regrowth rates were significantly reduced for the grasses.

While these results are encouraging in the short-term, repeated applications of dairy manures could potentially raise Cu concentrations to levels toxic to plants, with very limited possibilities for remediation. A few fields in Idaho that have received frequent applications of lagoon water have shown evidence of Cu accumulation. Because Cu is so tightly bound by the soil, it is very difficult to remove. Succeeding crops can only remove 0.1 pound Cu per acre per year. As it stands now, if a grower waits until Cu plant toxicity symptoms occur (including plant death), they will continue to see Cu toxicities in that field for an indefinite period of time.

Corn growing in various copper- treated soils. Inset photo: Corn two days following a 1,000 ppm soluble Cu treatment. Photo courtesy Jim Ippolito.

 

In terms of regulation, there is an existing EPA 503 “worst case scenario” standard that limits annual loading of Cu from biosolids to 66 pounds Cu per acre and limits lifetime loading to 1,339 pounds Cu per acre (limits are based on biosolids land application). For more information read Land Application of Biosolids. Reaching these limits is almost impossible with dairy waste applications, and would devastate most agricultural crops long before the lifetime loading limits were met. New York has set lower lifetime loading limits for Cu at 75 pounds per acre to avoid the potential of irreversible toxic accumulations of Cu in the soil. (For more information, see Table 5 in Composting Facilities.

Recommendations for Land Applying Copper Sulfate Hoof Baths

While more studies are needed to develop an official threshold for Cu in alkaline Idaho soils, based on what we know thus far, it would be advisable to cease Cu additions to soils with greater than 50 ppm extractable Cu. This value is advisable for producers raising alfalfa for dairy cow consumption in order to avoid Cu accumulation above National Research Council recommendations. To determine if you currently have a Cu accumulation problem in your soil, or to identify a developing accumulation, request an analysis for diethylenetriaminepentaacetic acid (DTPA) extractable Cu every two to three years from an accredited soil testing laboratory.

Recommended Reading

Authors

Jim Ippolito. Research Soil Scientist, USDA–ARS, Northwest Irrigation and Soils Research Laboratory, 3793 N. 3600 E., Kimberly, ID, 83341; 208/423-6524; jim.ippolito@ars.usda.gov

Amber Moore. Assistant Professor and Extension Soil Specialist, University of Idaho – Twin Falls Research and Extension Center, 315 Falls Avenue East, Evergreen Bldg., P.O. Box 1827, Twin Falls, ID, 83303-1827; 208/736-3629; amberm@uidaho.edu

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Environmental Impacts and Benefits of Manure: Phosphorous and Surface Water Protection

Managing manure nutrients in an environmentally and economically responsible manner is not a mutually exclusive endeavor. This article discusses phosphorus and its potential impacts on water quality.

Phosphorus and Water Quality

Phosphorous (P) is one of the major bio-available nutrients in manure. In aquatic ecosystems, P is typically the most limiting nutrient. When P is introduced into an aquatic ecosystem there is a marked increase in aquatic plant biomass production and increased algal blooms. The increased aquatic plant production and algal blooms can have a negative effect on the aquatic ecosystem such as tying up other nutrients and decreasing the amount of light infiltration.

At the end of the aquatic plant and algae growing cycles, there is a large release of excess nutrients into the ecosystem overwhelming the natural nutrient cycle, tying up oxygen during its degradation leading to fish kills and reducing surface water aesthetic qualities with the accumulation of rotting plant material on the water surface and offensive odors.

How Does Phosphorus Travel to Water?

In cropping systems, providing a sufficient level of P for plant uptake is as important as providing the proper levels of nitrogen (N) and potassium (K). Unlike N and K, P is bound to soil particles and is at low risk of leaching through the soil profile. The greatest risk of P loss from soils is with overland flow of runoff carrying P-enriched soil sediment or manure particles. Research has shown that soils testing high in P have a greater contribution effect for P loss than soils testing low in P.

However, there is a fraction of total P in runoff that is in the dissolved form. The sediment attached P and dissolved P have slightly different impacts in aquatic ecosystems. The sediment attached P contributes to long term P additions to the system whereas the dissolved P is readily available for a high rate of assimilation by aquatic plants and algae.

There are also reported cases of soils with extremely high levels of soil test P that are at risk of P leaching. Typically, soil P is bound tightly to soil particles and has a low risk of leaching. However, in some soils with extremely high soil test P levels, the exchange sites are at maximum capacity, leading to the risk of P leaching.

Blue-green algae bloom in nutrient impaired water. Source: Ron Wiederholt, NDSU Extension

 

Management Practices to Reduce Environmental Risks from Phosphorus

Cropping system practices that lead to reduced soil erosion are the most effective means of decreasing the risk of off-site movement of P. Besides soil erosion, there are other factors that need to be identified when reducing the risk of P loss from fields.

These factors include but are not limited to:

  • distance to surface water
  • slope of the landscape
  • soil erosivity index
  • soil test P level

Many states have adopted a process of ranking the risk of P loss from agricultural fields using a P-index. The USDA Natural Resources Conservation Service (NRCS) has been the lead agency in developing most of the state-by-state P-indexes. A P-index scores the factors important for off-site movement of P and by using the combined score of these factors a land manager can decide what options are best for managing P application levels to fields when using manure or commercial fertilizer.

However, the use of a P-index is only one of the tools available to nutrient managers. When there has been a long history of P mis-management and soil test P levels are extremely high, a P-index or other tools are not as effective. In these cases, a long term approach looking at the whole cropping and livestock system needs to be adopted.

Livestock rations must be closely monitored to ensure there is no P overfeeding (see the LPELC topic, Feed Management), manure may have to be sold or bartered to other land managers, or some type of intensive manure processing system will have to be adopted that will allow for more affordable long distance hauling of the manure (see the LPE Learning Center topic Manure Treatment Technology).

Recommended Reading On Phosphorus and Surface Water

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