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This article in AJ

  1. Vol. 77 No. 4, p. 630-633
    Received: Dec 15, 1983

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Comparison of Urea and Urea-Ammonium Polyphosphate with Ammonium Nitrate in Production of Tall Fescue1

  1. L. W. Murdock and
  2. W. W. Frye2



The yield response of tall fescue (Festuca arundinacea Schreb, cv. Kentucky 31) to urea (45% N) and urea-ammonium polyphosphate (34% N; 7.5% P) was compared with that from ammonium nitrate (33% N). The fertilizers were surface-applied to the fescue at a rate of 78 kg ha−1 N several times during the growing season. Ammonium nitrate and urea were applied twice per month from early April through mid-September of 1973, 1974, 1975, and 1977. Urea-ammonium polyphosphate was applied monthly during the same period of 1974, 1975, and 1977. Yield response, defined as yield with N fertilizer minus yield without N fertilizer, was significantly lower (P < 0.05) with urea than with ammonium nitrate at all application dates except mid-April and early May and September. The difference in September was significant at the 10% level. Yield response with urea-ammonium polyphosphate was not significantly different (P > 0.10) than with urea at the same application dates. The lower yield response to urea compared with ammonium nitrate was thought to result from volatilization loss of NH3. Fitted polynomials of the relationship between yield response to urea relative to ammonium nitrate (RRn) and the number of days following urea application until cumulative rainfall of at least 2.5, 5, 10, and 20 mm gave 2 values of 0.55, 0.54, 0.48, and 0.33, respectively; RR, values were usually higher when at least 2.5 mm of rain fell in < 3 days after application, and that amount of rainfall within that time appeared to be adequate to prevent large volatilization loss of NH3. The RRn values were usually lower when the first rainfall, regardless of amount, occurred > 3 days after application.

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