Manure Timing Matters: How To Reduce Phosphorus Loss

By Ehsan Ghane and Sarah Zeiler

Important takeaways

• Applying manure in December and January causes much higher phosphorus loss than in October and November.
• Applying manure soon after harvest in early fall reduces phosphorus loss.
• Winter flows dodge dormant vegetation, and even manure applied on unfrozen ground can freeze under snow and later wash out during thaw, as snowmelt and rain flush phosphorus into tile drains.
• If injection is not available, incorporate manure after surface broadcasting.
• Avoid spreading on frozen ground or before heavy rain.
• Plan storage early to prevent winter spreading.

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

Winter applications increase risk

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