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Agronomy Journal Abstract - Notes and Unique Phenomena



This article in AJ

  1. Vol. 97 No. 1, p. 338-342
    Received: July 13, 2004

    * Corresponding author(s): wrr@mail.pss.okstate.edu
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  1. W. R. Raun *a,
  2. J. B. Solieb,
  3. M. L. Stoneb,
  4. D. L. Zavodnyb,
  5. K. L. Martina and
  6. K. W. Freemana
  1. a Dep. of Plant and Soil Sciences, Oklahoma State Univ., Stillwater, OK 74078
    b Dep. of Biosystems and Agricultural Engineering, Oklahoma State Univ., Stillwater, OK 74078


Midseason fertilizer N is currently recommended using a wide range of differing soil-test, plant-test, and soil-N mineralization procedures. The objective of this paper is to present an applied approach for determining midseason fertilizer N rates. A conventional 2003 Honda FourTrax Foreman ES four-wheeler (433 cc, 127 cm wheel base, 116 cm wide) with a 3 m wide spray boom and a 1-m spacing between nozzles was modified to deliver a range of fixed N rates as urea ammonium nitrate (28%N) within a 9 m2 grid. Within each grid, nine separate 1 m2 areas exist, whereby each of the four corners receive no fertilizer N. Rates of 22, 45, 67, 90, and 112 kg N ha−1 occupy the other five, 1 m2 areas within the 9 m2 grid (termed as an N rate calibration stamp). Traveling at 8 km h−1 (5 mph), consecutive 9 m2 grids can be applied continuously. Calibration stamps should be applied preplant or soon thereafter and superimposed on top of the farmer practice. By midseason, differences between the 1 m2 N rate areas can be visualized and a field-specific topdress N rate prescribed by choosing the lowest N rate where no visual differences were observed between it and the highest rate. Calibration stamps applied preplant or soon after planting can assist in providing visual interpretation of N mineralization + atmospheric N deposition from planting to the time midseason N is applied, and improved determination of topdress N rates.

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