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This article in AJ

  1. Vol. 86 No. 1, p. 94-99
     
    Received: Jan 18, 1993
    Published: Jan, 1994


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doi:10.2134/agronj1994.00021962008600010018x

Ammonium and Nitrate Nitrogen in Soil Profiles of Long-Term Winter Wheat Fertilization Experiments

  1. Robert L. Westerman ,
  2. Randal K. Boman,
  3. William R. Raun and
  4. Gordon V. Johnson
  1. Dep. of Agronomy, Oklahoma State University, Stillwater, OK 74078

Abstract

Abstract

Accumulation of NH+4 -N and NO-3 -N in soils has not been thoroughly evaluated in long-term continuous winter wheat (Triticum aestivum L.) production systems. The objectives of this study were to determine long-term response of winter wheat to N fertilization and to evaluate accumulation of NH+4 -N and NO-3 -N in the soil profile. Four long-term winter wheat soil fertility experiments on thermic Ustoll soils that received annual applications of N for > 18 yr at selected N rates were sampled. At each location, one soil core 4.4 cm in diameter was taken to a depth of 240 cm from plots receiving variable N rates. Cores were separated into 30-cm increments and analyzed for 2 M KCI-extractable NH+4 -N and NO-3-N. At all locations, NH+4 -N levels were not significantly different from the check (no fertilizer N) when rates were applied at or below yield goal requirements (90 or 45 kg N ha−1 vs. 0 N). At N rates >90 kg N ha−1, surface (0–15 cm) NH+4 -N increased compared with the check, while subsurface NH+4 -N did not. Similarly, when N rates were <90 kg, N ha−1, no significant differences in either surface or subsurface NO-3 -N were found. At N rates >90 kg N ha−1, NO-3 -N accumulated in the subsurface soil profile (>30 cm). Estimates of N rates determined from simultaneous solutions of NO-3 -N accumulation minimums and yield maximums generated from quadratic regression were greater than N rates currently recommended to achieve yield goals at all locations. For these long-term continuous winter wheat experiments, no accumulation of NH+4-N and NO-3 -N occurred at recommended N rates where near maximum yields were obtained.

Contribution from the Okla. Agric. Exp. Stn.

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