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This article in AJ

  1. Vol. 100 No. 3, p. 658-664
     
    Received: May 17, 2006


    * Corresponding author(s): jun.zhang@wright.edu
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doi:10.2134/agronj2006.0154

Luxury Production of Leaf Chlorophyll and Mid-Season Recovery from Nitrogen Deficiencies in Corn

  1. Jun Zhang *a,
  2. Alfred M. Blackmerb,
  3. Jason W. Ellsworthc,
  4. Peter M. Kyverygad and
  5. Tracy M. Blackmerd
  1. a Statistical Consulting Center, Wright State Univ., 130 MM Bldg., 3640 Colonel Glenn Hwy., Dayton, OH 45435
    b Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
    c Wilbur Ellis Company, 150 Burlington St., Pasco, WA 99301
    d Iowa Soybean Association, 4554 114th St., Urbandale, IA 50322

Abstract

Deficiencies of N during the growth of corn (Zea mays L.) are often diagnosed by using chlorophyll meters that measure chlorophyll content in leaves. The diagnoses are based on the assumption that above-optimal supplies of N do not significantly influence chlorophyll meter readings (CMRs). The objective of this research was to assess the possibility that above-optimal supplies of N impacted chlorophyll concentration and the effects imposed a limitation on the minimum N deficiencies that can be detected by chlorophyll meters. Our approach was to monitor temporal patterns in CMRs of nonirrigated corn that received various rates of N at various times. The results showed that the time at which N deficiency symptoms first become detectable was closely related to the amounts by which N rates fell short for maximizing grain yield. The measured symptoms of N deficiency changed with time. Temporal patterns in CMRs were affected by N treatments while yields were not greatly affected. In-season N applications made to plants that started to show N deficiencies caused CMRs to converge with those taken on plants that always had adequate N. These observations suggest that above-optimal supplies of N may induce a luxury production of chlorophyll that is analogous to luxury uptake of nutrients. These problems severely limit the value of using chlorophyll meters to guide in-season fertilization in fields having near-optimal supplies of N. The underlying problem is the uncertainty caused by difficulties associated with distinguishing luxury production of chlorophyll from symptoms of N deficiencies.

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Copyright © 2008. American Society of AgronomyCopyright © 2008 by the American Society of Agronomy