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Superintendent
David Davis
21262 Genoa Road
Linneus, MO 64653
Phone: 660 895-5121
FAX: 660 895=5122
Email: DavisDK@missouri.edu

Forage Systems Update
Vol 15, No. 2

About half of Missouri's 12 million acres of tall fescue receive nitrogen (N) fertilizer either in the spring or late summer to increase yields. Because ammonium nitrate is being phased out and urea has NH3 volatilization problems, growers need comparative information on new N products for pastures.

Our objectives were: 1) to compare ammonium sulfate, ammonium nitrate, urea, ESN coated urea, Nurea, and Nurea with NITAMIN, and mixtures of ammonium sulfate with urea and ESN as N sources for tall fescue in spring and late-summer applications.

Plots were established at the Forage Systems Research Center (FSRC) and at the Southwest Missouri Research and Education Center (SWC). Each of the fertilizer sources and mixtures listed in Table 1 were applied in mid-March (spring) and mid-August (late-summer) in separate experiments at each location. The nitrogen fertilizer application rate was 75 lb/acre N. For the spring application, forage was harvested in late May, late July, and mid-October to measure season-long pasture production. For the late-summer application, plots were harvested in early December and indicate the suitability of each source for growing "stockpiled" forage.

When the nitrogen was applied in spring, only the May harvest responded to N at either location (Tables 2 and 3). We hypothesized that the "coated urea" products such as ESN might have yielded greater in the summer and perhaps early autumn because of their slow N release activity. However, a dry summer in 2005 may have slowed plant growth enough that slowly available N released by the coated products was not utilized. Thus, no benefit would have been realized from the coated products. We found that ammonium sulfate ranked in the top producing group at nearly all harvests and locations. This is surprising in that we typically do not expect a response to sulfur from tall fescue pastures in Missouri. Another somewhat surprising result from this first year was that ammonium nitrate provided no better yields than urea. Each location received nearly 1.0 inch of rain within 5 days of the fertilizer application and most likely, this precipitation was sufficient to get urea into the soil solution. As a result of the timely rainfall in spring, the advantages of coated products such as ESN may have been masked.

For the late-summer application at FSRC, all of the products applied yielded equally and were about 2 times greater than the unfertilized control (Table 4). Rainfall of 1.35 inches fell there within 3 days of the N being applied and so volatilization of NH3 was likely not an issue. At SWC, there were treatment differences for the late-summer application, but they are difficult to interpret. The ESN coated urea when mixed with ammonium sulfate (rate of 10 lb/acre S) and in the three-way mixture of ammonium sulfate-ESN-Urea was in the top yielding group. By itself, ESN yielded less than these mixtures. Ammonia volatilization may have been the cause for these treatment differences as only 0.27 inches of rainfall came 6 days after the N was applied. It is interesting that additional coated urea products did not show an advantage. Perhaps there is some benefit to having mixtures of ESN with ammonium sulfate in dry weather.

Forage quality samples are being processed at this time for crude protein, ADF, NDF, and iNDF. None of this data is available at present, but will be included in future reports.

Table 1. Nitrogen fertilization treatments being tested at the Southwest Research Center near Mt. Vernon and at the Forage Systems Research Center near Linneus, Missouri. Each source is applied to deliver 75 lb/acre N. In addition, rate mixtures of ammonium sulfate/ESN, ammonium sulfate/urea and urea/ammonium sulfate/ESN are included.

Table 2. Tall fescue yields over the entire growing season when treated with different N sources at the Southwest Missouri Center near Mt. Vernon, Missouri. Nitrogen was applied at 75 lb/acre in mid-March, 2005.

Table 3. Tall fescue yields over the entire growing season when treated with different N sources at the Forage Systems Research Center near Linneus, Missouri. Nitrogen was applied at 75 lb/acre in mid-March, 2005.

Table 4. Yield of fall grown tall fescue treated with different N sources at Southwest Research Center (SWC) and at the Forage Systems Research Center (FSRC). Nitrogen was applied at 75 lb/acre in mid-August, 2005 and forage harvested in early December.