Manure is an excellent source of crop nutrients. Applying it at the wrong time, though — especially during winter when tile drainage is more active — can greatly increase phosphorus loss. This poses risks to water quality.

In a six-year Michigan study (2019 to 2024), manure applied in December and January lost 1.1 pounds per acre of total phosphorus, compared to only 0.13 pounds per acre when applied in October and November. Dissolved phosphorus losses were 0.71 pounds per acre in winter versus 0.12 pounds per acre in fall.

These losses represent phosphorus from recent manure applications only and do not include legacy phosphorus already present in the soil. This distinction shows the direct impact of winter manure spreading.

There are a few reasons why phosphorus losses are much higher in December and January than in October and November.

1. More tile flow in winter: After dry fall months, winter precipitation restores flow, bypasses dormant vegetation, and carries phosphorus into drains.
2. Freeze-thaw cycles: The southeast Michigan field experienced seven to 10 freeze-thaw cycles per season, often combined with rain-on-snow events, which historically are only three to five cycles. Even when manure was applied on unfrozen, bare ground in winter, the next snowfall froze it in place. During subsequent thawing, snowmelt and rain create tile flow that flushes phosphorus previously locked in frozen soil. Similar observations have been made in Wisconsin.
3. Higher winter application rates: Winter applications averaged 124 pounds per acre of phosphorus, compared to 81 pounds per acre in fall. Even with only 50% more manure applied, winter losses were six to eight times higher because additional drainage flow is the dominant driver of phosphorus loss.

There are management practices that can reduce this risk. Spreading manure soon after harvest, when soils are dry, gives phosphorus time to bond with the soil and reduces the risk of leaching.

Installation of controlled drainage — structures with weirs or gates — slows down tile flow after manure application, reducing phosphorus loss during the first big flow event. Michigan research shows this practice is more effective at reducing phosphorus loss than conventional free drainage.

As for application, if injection isn’t available, incorporate manure with low-disturbance tillage after surface broadcasting. This mixes manure into the soil, boosting contact with soil and reducing phosphorus loss.

Plan ahead for storage

Manure storage gives farmers flexibility to apply manure at the right time for crop growth, rather than when weather or field conditions are unfavorable. Without adequate storage, farmers may be forced to apply manure during high-risk periods, such as rain or snowmelt, increasing environmental loss. Proper storage improves timing and placement, helping protect water quality. Planning ahead can prevent these risks. Keep in mind that winter weather can affect the integrity of storage structures. Read more on page 13.

Know your requirements

Livestock producers should follow their state and local regulations and best management practices for manure management and utilization. Key winter application practices to consider include:

• Avoid spreading on frozen or snow-covered soils whenever possible. If necessary, apply solid manure on fields with slopes less than or equal to 6% and liquid manure on fields with slopes less than or equal to 3%.
• Use controlled drainage to reduce phosphorus loss.
• Incorporate manure when possible.
• Use conservation practices such as vegetative buffer strips to reduce runoff and erosion.
• Maintain a 150-foot buffer from surface water inlets and concentrated flow areas.
• Assess fields using the Manure Application Risk Index (MARI), which rates sites based on 12 factors, including slope, soil type, phosphorus levels, setbacks, buffer width, and application method. Fields rated Very Low (less than 19) or Low (19 to 37) are best for winter spreading.

Concentrated Animal Feeding Operations (CAFO) must comply with National Pollutant Discharge Elimination System (NPDES) permit rules, including having storage for six months of manure, which generally allows them to avoid winter spreading. For local rules, contact your Natural Resources Conservation Service (NRCS) conservation technician or soil and water conservation district.