Soil Fertility

Soil Fertility and Manure Management

A soil fertility program for corn silage should maximize yields of high quality forage without using excess nutrients, which wastes money and can lead to nutrient runoff or leaching. Corn harvested for silage removes large amounts of nutrients (figure 1), resulting in substantial fertilizer recommendations. Corn silage is often grown in rotation with legume forage crops and on land that has a history of manure applications. Therefore, it is essential to consider the nutrient contributions of previous crops and manures to avoid excessive fertilization and keep production costs down. These soils may also have high residual levels of phosphorus and potassium from repeated manure applications. Consequently, soil testing is an essential aspect of soil nutrient management for corn silage. Many state and private laboratories can provide soil testing services and recommendations.

Good soil fertility management can improve the forage quality of the silage. The protein content of corn silage increases as the availability of nitrogen increases. Low protein silage is a signal that nitrogen was defiant during the growing season. This deficiency may be a result of nitrogen rates that were too low, excess nitrogen losses caused by wet weather, or a weed infestation that compared with the crop for nitrogen. Research in Pennsylvania has shown that nitrogen rates should be increased by about 20 lb/acre compared to grain based on the feed value of corn silage. Nonprotein nitrogen (NPN) additions to the silage can be used to increase protein concentrations above those needed for maximum yield. High potassium levels in the silage may be undesirable for some feeding programs and may be an indicator of excessive potassium availability. This may be encountered on fields with repeated, heavy applications of cattle manure.

Since corn silage is often produced on livestock farms where manure is available, appropriate management of the manure resources is critical to maximize profitability. Because of the lack of crop residue on corn silage fields, manure applications should be managed to minimize potential runoff problems by using cover crops or incorporating the manure where necessary.

Further Reading


Note: Web resources for Wisconsin are maintained by Mike Rankin and Team Forage. Please see for an up-to-date listing.

New N Rate Application Guidelines for Corn
by Carrie Laboski, UW Extension Soils Scientist

Nutrient Application Guidelines for Field, Vegetable and Fruit Crops
UW Extension Bulletin A2809 - available for viewing only in a .pdf format.  Provides current soil test and fertilizer recommendations for all field crops.

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