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Early fall applied manure can lead to corn yield loss

Iowa State University Extension and Outreach
Applying manure before soils have cooled to below 50°F can be a costly decision.

The early harvest this year has created opportunities to complete fall field work and manure applications much earlier than usual. However, applying manure before soils have cooled to below 50°F can be a costly decision. Pushing manure application to later in the fall or waiting until spring can help to prevent nitrogen loss and better match nutrient availability with nutrient demand by crops.

A research trial at the ISU Northeast Research and Demonstration Farm near Nashua, Iowa, found significant yield reductions when fall manure was applied when soil temperatures exceeded 50°F. In a corn-soybean rotation, late fall applied manure (soils < 50°F) averaged 40 bushels/acre greater corn yield than early fall manure over a three-year period from 2016 to 2018.

Weather conditions in fall 2018 prevented the early to late fall manure comparison for 2019. However, in a late fall to spring manure comparison, the spring manure treatment had an 18 bushels/acre yield advantage. Similarly, a late fall to spring manure comparison in continuous corn showed a 38 bushels/acre yield advantage (three-year average) for the spring-applied manure. Research conducted at other locations has also reported yield advantages with delaying manure application timing.

There is always a possibility of poor weather conditions if manure application is delayed, but this needs to be compared with the risk of nitrogen loss and lower yields when manure is applied too early in the fall. See this ICM blog at https://bit.ly/3j09SpR for more information, including the effects of a cereal rye cover crop with early-fall applied manure.