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Agronomy Journal Abstract -

Soil and Tissue Nitrate Tests Compared for Predicting Soil Nitrogen Availability to Corn


This article in AJ

  1. Vol. 81 No. 6, p. 971-974
    Received: Oct 31, 1988

    * Corresponding author(s):
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  1. R. H. Fox ,
  2. G. W. Roth,
  3. K. V. Iversen and
  4. W. P. Piekielek
  1. Dep. of Agronomy, Pennsylvania State Univ., PA 16802.



Mounting concern about NO3 pollution of the nation's ground and surface waters make accurate N-fertilizer recommendations increasingly important. A study was initiated in 1984 to determine if presidedress soil or corn stalk (Zea mays L.) NO3 concentrations could be used to predict soil N availability and the need for sidedress N fertilizer. Nitrate concentration was determined in the surface 30 cm of soil and in the lower 10 cm of corn stalks 22 to 37 d after emergence (corn was in the 5- to 6-leaf stage). Eighty-seven N-response experiments were conducted over a 4-yr period in central and southern Pennsylvania. A number of these sites were on fields that had received high rates of manure in the past. Corn stalk NO3 concentration was not an accurate predictor of soil N availability nor of the probability that a site would respond to N fertilizer. The NO3 concentration in the surface 30 cm of soil 4 to 5 wk after emergence was a good indicator of whether a response to sidedress N fertilizer would be attained. The best critical level for separating responsive from nonresponsive sites was 21 mg NO3-N kg. No sites responded to N fertilizer when the soil NO3-N concentration was greater than 25 mg kg. Soil NO3 concentration and soil N-supplying capability (NSC) at soil NO3 levels below the critical level were not correlated well enough (r2 = 0.34) to use the predicted NSC for adjusting N-fertilizer recommendations. As a result, the best use of this test in Pennsylvania appears to be in identification of nonresponsive sites rather than predicting N-fertilizer rates. Use of this test by farmers in Pennsylvania will help minimize the practice of applying “insurance” N when N contributions from manure and legumes in rotations are uncertain.

Paper no. 8030 of the Journal Series of the Pennsylvania Agric. Exp. Stn.

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