Reducing the Risk of P Losses from Manure Applied to Frozen Soils
Spreading manure, solid or liquid, on frozen soils can lead to large P losses to runoff during the spring melt or if rain falls before the soil thaws. There is an especially large risk of manure P loss in runoff when snow melts quickly and large volumes of water run over frozen ground. In some years, the snow melts slowly, and if the manure has been applied on shallow slopes, the P has an opportunity to react with the soil and even sink in. Then the risk of loss may be very low. But in years with rapid melting, and on ground that froze wet, there may be substantial losses. Not only P is lost, but also valuable nitrogen and organic matter, which can cause other water quality problems. One way to reduce P Index values for fields with winter manure applications is to choose sites with lower winter runoff potential. P Index calculations assign low risk to sites that have:
- Less than 6% slope.
- A rough surface with depressions that will capture snowmelt runoff, such as fields that are fall-tilled on the contour.
