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.
Note: Web resources for Wisconsin are maintained by Mike Rankin and
Team Forage. Please see http://www.uwex.edu/ces/crops/uwforage/Silage.htm for an up-to-date
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.