Nitrogen Sources for Stockpiling Fescue

Farm Business Management Update, August 2002

By Scott Jessee

If you attend any forage production meetings during the late summer or early fall in Virginia, you will more than likely hear about stockpiling tall fescue. Stockpiled fescue is a very nutritious, storable forage with most samples testing around 60% TDN (energy) and 12% Crude Protein. Without doubt by extending the grazing season, production costs can be decreased.

Dr. Jim Gerrish, University of Missouri, has done a tremendous amount of research in fescue fertilization and timing of nitrogen applications. If pastures receive a nitrogen application of 60 pounds by mid-August, you can potentially produce 3,000 pounds of dry matter per acre (assuming suitable weather). Data from these University of Missouri trials are presented in Figure 1:

Figure 2: Fescue Response to Nitrogen Application

If you decide to try stockpiling as a forage management option, you must choose a nitrogen source. In Southwest Virginia three commercial nitrogen sources are commonly used: ammonium nitrate, ammonium sulfate, and urea. Characteristics of each fertilizer material are listed in Table 1.

Table 1. Characteristics Of Fertilizer Materials

	Ammonium Nitrate	Ammonium Sulfate	Urea
% Nitrogen per pound	34	21 N and 24 S	46
Pounds N per ton	680	420 N and 480 S	920
Material type	Dry granular	Dry granular	Dry granular
Nitrogen Availability	100% water soluble, readily available	100% water soluble, readily available	100% water soluble, readily available
Volatilization Potential (loss to atmosphere)	Low loss for surface applications	Low loss for surface applications	High loss potential for surface applications if weather is warm.

All nitrogen sources described can be utilized for stockpiling tall fescue. Special attention needs to be given to urea, especially if the weather is warm and no rain is expected. Volatilization losses can be as high as 20 percent (12 pounds of N). Urea is a good option if rainfall is expected soon after application. Approximately 1/3 inch of precipitation will move urea into the soil and will reduce losses to almost zero. For soils with low pH, ammonium sulfate should be avoided due to the negative effects on soil pH.

Costs

Although each material will supply nitrogen, you must analyze your production situation as well as the current weather pattern to be most cost effective. In areas experiencing moderate to severe drought in August, applying nitrogen for stockpiling could be unrewarding. For areas receiving rainfall, producers have more production options. In Table 2, current nitrogen fertilizer costs are compared.

Table 2. Comparison of Current Fertilizer Costs

	Ammonium Nitrate	Ammonium Sulfate	Urea
Cost per ton	$240	$220	$220
Cost per Pound of N	$0.35	$0.52	$0.24
Cost of 60# N application per acre	$21.17	$31.43	$14.35

Although ammonium sulfate is the highest cost source of nitrogen, you need to remember that you are also getting 480 pounds of sulfate, which affects soil pH. Urea is the cheapest source, but it has the highest volatilization potential of the three sources discussed. If little rainfall is expected, an increased rate of urea could be used and the application would still be cost-effective (20% increase in application rate would increase the cost per acre by only $2.93).

Conclusion

Each growing season is unique. Differences in weather patterns across our state cause some areas to be highly productive while other areas are implementing drought-survival tactics. Stockpiling can extend our grazing season if weather conditions are favorable. Contact your local extension agent to discuss nitrogen sources and application rates for stockpiling and other fall management practices.

Contact the author at djessee@vt.edu.

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