Reducing the Risk of P Losses from Unincorporated Manure or Fertilizer
A portion of the P in fertilizers and manures left on the soil surface will be lost if runoff occurs soon after application. Practices that can reduce the risk of this kind of loss from unfrozen soils are:
- Lowering manure application rates
- Lowering the P content of the manure by lowering feed P
- Applying in the spring rather than the fall. The PI acute loss risk on unfrozen soils is greatest in the fall and least in the spring.
In research trials on silt loam soils with good drainage, runoff volumes and total runoff P losses following manure applications have been much
greater in the fall than in the spring. This has been attributed to greater soil surface sealing in the fall at the end of the growing season.
This only works on soils that are fairly well drained.
- Avoiding fields with heavy or poorly drained soils if possible. Unincorporated applications on these types of soils have resulted in higher runoff P losses than on well-drained silt loam soils.
