top of page

Managing Soil Phosphorus: Opportunities for Dairy Farms

Phosphorus is an important nutrient on dairy farms and a source of environmental risk through accumulation of phosphorus in the soil. Farmers can work with their nutritionists and crop advisors to implement strategies to manage phosphorus levels from the dairy production area and to help protect water quality.

Learning HubManaging Soil phosphorus 

CONTENT CURRENTLY UNDER DEVELOPMENT
soil-hero.jpg

Digital Resources

Summary Presentation

SPEAKER: Beth Gruden

Downloadable Resources

Customizable Shareable Presentation

Summary of Key Points from the Presentation

Phosphorus

Phosphorus is a vital nutrient that plays a crucial role in a cow's diet for bone development and overall health. It is also essential for crop growth as it supports energy transfer, plant respiration, cell division, photosynthesis, and many other plant processes.

Phosphorus often receives the attention from crop consultants, regulators, and environmentalists because when it leaves a farm in runoff, phosphorus can degrade the quality of lakes and streams. Specifically, phosphorus additions into freshwater lakes and streams can stimulate the excessive growth of algae and aquatic weeds. A potential consequence of this stimulated growth can be odors, fish kills, and an overall reduction in the recreational value of lakes.

Phosphorus Loss Pathways

Phosphorus loss from agricultural fields primarily occurs through surface runoff, which accounts for the majority of phosphorus transport to nearby water bodies. Phosphorus is generally non-soluble and tends to bind with soil particles, making it susceptible to loss through erosion. During rainfall or irrigation events, water moves across the field surface, picking up phosphorous particles from soil, manure, and fertilizers. This process is particularly significant on sloped or compacted fields, where infiltration is limited, causing phosphorus attached to soil particles (particulate phosphorus) and dissolved phosphorus to flow into streams and lakes. Subsurface leaching is a less common pathway for phosphorus loss, generally restricted to sandy soils or areas with high water tables where dissolved phosphorus can migrate downward through the soil

 Reducing the Phosphorus Concentration of Manure

Dairy Cow Precision Feeding

Dairy farms can significantly reduce phosphorus excretion in manure. Reducing or eliminating supplemental phosphorus in rations and using phytase to enhance phosphorus availability and utilization can reduce excretion levels.

Separating Manure Solids from Liquids

Manure separation enables more precise nutrient application. Fine solids, where phosphorus is concentrated, can be separated mechanically (e.g., centrifuges and vibrating screens) or chemically (e.g., chemical flocculation and dewatering). Concentrating phosphorus in the solid fraction leaves the liquid fraction with nearly all the soluble nitrogen (ammonium, nitrates, nitrites) and potassium. This allows for different application rates for the solid and liquid portions to better match crop needs. It can also allow for a more cost-effective option for transporting the phosphorus laden solids a greater distance.

Learn More

Please note that we cannot confirm the accuracy or reliability of the materials found on external websites linked here.

Phosphorus Build-up and Loss

Phosphorus buildup is primarily a concern in certain U.S. regions — like the Northeast, Midwest, and Southeast — due to a combination of soil types, climatic conditions, land use, and agricultural practices. Several factors contribute to phosphorous accumulation:

​​

  • Historical fertilization practices: Decades of phosphorus application, both as manure and synthetic fertilizer, contribute to legacy phosphorus in the soil, where past applications still impact soil phosphorus levels, especially in regions with less P uptake by crops.​

  • Imported feeds: Imported feeds used on dairy farms bring more nutrients to the operation and can increase the concentration of nutrients within the farm boundary, particularly phosphorus.

  • Crop nutrient needs: The ratio of phosphorus to nitrogen in manure does not match the typical nutrient uptake needs of most crops. To meet the nitrogen requirements of crops, farmers may apply manure at rates that exceed the phosphorus needs, leading to an accumulation of phosphorus in the soil.

  • Manure application location: Manure, being naturally high in phosphorus, is often applied to nearby fields since transporting it farther away is both costly and logistically challenging. Land application on closer fields also reduces the time required to apply the manure. As a result, farmers may over apply manure on fields closer to the farm to manage the surplus.

  • Soil type: Farms may over apply manure to lighter textured soils (such as sands or sandy loams) as lighter soils dry faster so may be more readily available to spread manure on during the wetter months. These fields can be less productive, leading to phosphorus building up. Additionally, many of these soils are lower in organic matter and have lower nutrient holding capacities which can lead to increase leaching or runoff of these nutrients. This tends to be an issue on sand fields associated with dairies, particularly when the dairy lacks adequate manure storage.​​

It can take decades to reduce built-up phosphorus.​​​​​ Solving this problem requires a holistic approach that considers the individual farm, resources, and local environment.

Increasing Crop Phosphorus Uptake and Removal

Double or Triple Crop

Double and triple cropping, growing multiple crops within the same calendar year, can significantly enhance phosphorus uptake and removal by increasing the amount of manure utilized. This practice is particularly beneficial for farms with limited acreage as it allows more manure to be applied per acre. Depending on the soil phosphorus levels, it may be necessary for the dairy operation to evaluate crop uptakes of phosphorus to determine the most efficient crops to plant in the system.

Perennial Legumes

When properly managed and cared for, crops like alfalfa can be used to draw down soil phosphorus concentrations significantly in a multi-year rotation. These legumes rely on bacteria in the plant roots to fix nitrogen from the atmosphere which makes it available to the crop. Since manure will not be applied to these fields, additional acreage will be needed for the application of remaining or excess manure.

Related Practices Or Technologies

Improving Phosphorus-Rich Manure Distribution

The high-water content of liquid and slurry manure makes it heavy and costly to transport, especially over long distances. Over-applying nutrients, especially in liquid form, can lead to runoff and pollution of nearby water bodies. Spreading manure over a larger area helps distribute nutrients more evenly across the available land. This can prevent nutrient build-up and potential environmental issues. This strategy will generally require a commercial fertilizer pass for crops that are limited by nitrogen.

Reducing Water Added to Manure

Reducing the amount of added water to manure is an effective strategy for minimizing the volume and weight of manure that needs to be transported, thus making it more cost-effective to handle. Farms can achieve this by switching from flush systems to scrape or vacuum systems that mechanically remove manure without adding water. Additionally, farms can reduce water in manure by keeping clean farmstead water separated from the manure and covering manure lagoons or pits to prevent rainwater from mixing with manure.

Removing the Water in Manure

Farms can reduce transport costs by using manure technologies such as solar drying, composting, and de-watering to lower the water content in manure. Solar drying involves spreading manure in a thin layer and exposing it to sunlight, which evaporates the water, resulting in drier, lighter manure. Composting mixes manure with organic materials to promote microbial activity, generating heat that reduces moisture content and volume. De-watering uses mechanical processes, such as centrifuges or presses, to physically remove water from manure. These technologies decrease the volume and weight of manure, making it easier and more cost-effective to transport, and can improve the value as a fertilizer. Note that many de-watering techniques can cause the loss of the available nitrogen in manure. Farms should work with advisors to ensure practices balance nutrients with crop requirements.

Reducing Manure Transport Costs with Draglines and Manure Pipelines

Dragline technology enables the transportation of manure up to 5 miles, with booster pumps placed along the route to maintain pressure. Additionally, many farms are now installing permanent piping systems — both above and below ground — to streamline the transport of manure over long distances, up to 10 miles from the farm. Pumping manure makes it more economical to transport to outlying fields and improve manure distribution.

Applying Manure on a Phosphorus Basis

Applying Manure on a Phosphorus Basis

Applying manure on a phosphorus basis means determining the application rate of manure primarily based on the phosphorus needs of the crop. Meeting crop nitrogen needs with manure application often results in over-application of phosphorus, especially for corn. Applying manure on a phosphorus basis typically requires a lower application rate, therefore commercial fertilizers will likely be necessary to balance nitrogen and potassium requirements.​​​

Related Practices Or Technologies

Exporting Manure

Exporting manure to fields farther from the farm or to other farms can help reduce the buildup of phosphorus in the soil by spreading the nutrient load more evenly across a larger area. This practice not only prevents excessive phosphorus accumulation near the source but also allows other fields that may be deficient in phosphorus to benefit from the manure's nutrient content, thereby promoting more balanced soil health. Generating a manure byproduct such as soil amendment or compost can also create an additional income stream for the operation.​

Preventing Phosphorus from Entering Waterways

Most phosphorus is lost via erosion because it is attached to soil and manure organic matter. Therefore, practices that prevent erosion can prevent phosphorus from entering waterways.

  • Preventing rill/sheet erosion: Implementing practices like cover cropping, planting perennials, contour farming, strip cropping, and maintaining ground cover can significantly reduce rill and sheet erosion, thereby minimizing phosphorus loss attached to soil particles.

  • Preventing concentrated flow erosion: Creating buffer strips and using grassed waterways can help prevent concentrated flow erosion, reducing the transport of phosphorus-laden soil into water bodies.

  • Intercepting run-off before it enters waterways: Installing riparian buffers and sediment control structures can effectively intercept and filter run-off, capturing phosphorus before it reaches waterways and contributes to pollution.

  • Utilizing precision farming: Utilizing equipment and technologies for precision farming can improve nutrient application and vary application rates based on soils, topography and soil tests. Placing the manure where it is needed will reduce runoff potential of phosphorus.

  • Manure injection or incorporation: Utilizing manure injection equipment or incorporating manure soon after it is applied can reduce the amount of nitrogen lost through volatilization. This can help to better balance the nitrogen-phosphorus ratio. Additional crop land may be needed for the most efficient use of the nutrients. Injection and incorporation can also reduce the phosphorus runoff potential.

bottom of page