By Rachel Milliron, Extension Educator
Nutrients, like nitrogen (N) and phosphorus (P), tend to be more vulnerable to loss after fall manure applications than spring applications due to: 1) a lack of crops grown in fields, and 2) the longer period of time that manure is left in the field. To reduce losses, consider planting a cover crop and delaying manure applications.
Planting a cover crop in fields that will receive fall manure, can improve crop recovery of manure-N. Additionally, planting a cover crop like rye, wheat or triticale can also provide soil coverage throughout the winter; reduce erosion and runoff; and provide additional forage if harvested.
With a short planting window in the fall, it is important to drill cover crops soon after crop harvests. Manure applications can be delayed after cover crop planting to ensure crop establishment and good soil coverage throughout winter. Waiting to apply the manure when temperatures are cooler, has the additional benefit of significantly reducing N-volatilization losses and increase manure-N availability for crops, even when manure is not incorporated. The rule of thumb is to apply manure when soil temperatures stay consistently below 50 F. If applying manure during the winter, 25% residue or coverage from a cover crop is required.
It is not always possible to delay manure applications after cover crop establishment, especially when manure storages are full.
When manure is applied early in the fall, warmer temperatures and time constraints present challenges. Higher temperatures drive N-volatilization losses and if manure is not incorporated within 2 days, around 80% of available manure-N can be lost. Incorporating manure with tillage can reduce volatilization losses, but increases the potential for erosion and runoff and delays cover crop planting. Low-disturbance injectors, like a shallow disc injector, would be a good application method for early fall manure. It provides manure application and incorporation in one pass, is an option for no-till, and reduces the time needed to apply manure before planting a cover crop.
For more information on how to calculate manure-N availability can be found in the Penn State Agronomy Guide.