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This article in AJ

  1. Vol. 87 No. 3, p. 403-408
     
    Received: Mar 10, 1994
    Published: May, 1995


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doi:10.2134/agronj1995.00021962008700030003x

Use of a Chlorophyll Meter at the Early Dent Stage of Corn to Evaluate Nitrogen Sufficiency

  1. William P. Piekielek ,
  2. Richard H. Fox,
  3. John D. Toth and
  4. Kirsten E. Macneal
  1. Dep. of Agronomy, 116 Agric. Sci. and Indust. Bldg., The Pennsylvania State Univ., University Park, PA 1680

Abstract

Abstract

A late-season chlorophyll meter test for corn (Zea mays L.) could provide growers with a convenient evaluation of that year's N management program, along with information useful for N fertilizer rate decisions in subsequent growing seasons. Chlorophyll meter (SPAD 502) readings were taken late in the growing season on corn ear leaves in replicated plots of 357 N treatments from 93 N-response experiments conducted in Pennsylvania. At sites not affected by severe late-season drought or disease, chlorophyll meter readings taken at the 1/4 milk line stage separated N-deficient from N-sufficient treatments with 93% accuracy using a critical level of 52.0 SPAD units. If meter readings were normalized at each site by comparison with a site-specific high-N reference reading, chlorophyll meter readings of ear leaves made from the late milk to the middent stage of corn could separate N-deficient from N-sufficient treatments with 92% accuracy using a relative SPAD reading critical level of 0.93. For treatments with meter readings below the critical level, relative grain yields and the additional N that would have been needed for economic optimum grain yield were correlated with chlorophyll meter test values. ]For treatments with a meter reading above 52.0 SPAD units, the amount of excess N that may have been applied could not be accurately predicted. For corn tested at the 1/4 milk line stage, we suggest an N-sufficiency range of 52.0 to 56.0 SPAD units, above which there is a 70% probability of an excess of > 50 kg N ha−1 having been applied.

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