Why Consider Late Fall Nitrogen Fertilization?
Most of you would agree that anytime in the fall is a good time to apply phosphorus and potassium on forage grass stands. These nutrients aid in winter stand survival, root growth and general tolerance to plant stress. Generally we do not recommend N application after mid-September because it may over stimulate lush growth when the plant should be preparing for winter. The theory behind late fall nitrogen fertilization of cool season grasses is very simple. Apply low rates of N fertilizer (40 to 50 lbs/acre) in the late fall (mid October to late November) when cool temperatures have reduced top growth, but root growth is still active. The N is used to "set-up the plant" for winter and for healthy early spring growth. Not only does enhanced root growth aid in the uptake of water and nutrients, carbohydrate buildup in the stem bases promotes winter survival and spring regrowth.
Although research results are not absolute, late fall nitrogen applications to cool season grasses have the potential to enhance stands and spring forage yields. The following advantages are suggested based on research by Dr. Dale Wolf and long standing practices with Turfgrass stands.
Late Fall Nitrogen Application Timing and Rates
Nitrogen should be applied in mid to late fall once the topgrowth of cool season grasses begins to stop. This is generally mid October to late November depending on the area of the state. When applying nitrogen it is important to use a highly soluble sources (eg. Urea, ammonium nitrate, ammonium sulfate, liquid UAN). Organic forms of nitrogen (eg. animal manure) will not have the same effect on cool season grasses in late fall. Although some N in manure is in the soluble ammonium form, the majority is tied up in organic compounds and requires warm temperatures and microbial breakdown before it becomes plant available.
Once hard frosts cause the deterioration of leaf tissue, N applications are not recommended because plant uptake is minimal and applied N is wasted.
In conclusion, low rates of N (40 to 50 lb/acre) applied in the late fall to cool season grasses have been shown to improve root growth, spring regrowth, stand density, and maintain or improve forage yield. Under hay production, additional spring or early summer N applications are required for maximum production.
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