Alternative Nitrogen Fertilizers to Ammonium Nitrate for Tall Fescue Pastures.

Efficient nitrogen (N) management of grass pasture is one of the most important factors for successful forage-livestock production systems. Ammonium nitrate and urea have been the most popular sources of N for grass forage production in the Midwest. However, ammonium nitrate is a security issue for the fertilizer industry because it can be used as an explosive. Its availability is scarce compared to 10 years ago. Surface application of urea, on the other hand, can be problematic due to nitrogen volatilization. These issues are driving producers to look at alternative forms of N fertilizer for pastures. The objective was to compare forage production in tall fescue pastures treated with ammonium nitrate, urea, ammonium sulfate, coated urea products, and mixtures containing ammonium sulfate, urea, and ammonium sulfate with polymer coated urea. We fertilized established tall fescue pasture with six different N sources in mid-March and mid-August in separate experiments at two locations in Missouri during 2005, 2006 and 2007. The fertilizer application rate was 84 kg N ha^-1 yr^-1. For the spring N-fertilized plots, forage harvest occurred in late May, late July, and mid-October. Plots fertilized in late-summer were harvested in early December. The experiment was a randomized complete block design with five replicates. Treatment with ammonium sulfate produced yields as good as ammonium nitrate treatment at almost all harvests and locations. Additionally, ammonium nitrate, urea, and ammonium sulfate did not differ as N fertilizer sources for tall fescue in spring. For late-summer N fertilized plots, most of the products yielded similarly. Urea, ammonium nitrate, and ammonium sulfate had comparable yields in most site-years. However, in the dry autumn of 2005, tall fescue fertilized with urea yielded 35% less than that fertilized with ammonium nitrate or ammonium sulfate. Data will be discussed in details in the poster presentation.