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This article in AJ

  1. Vol. 88 No. 1, p. 1-5
     
    Received: June 7, 1994
    Published: Jan, 1996


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doi:10.2134/agronj1996.00021962008800010001x

Nitrogen Deficiency Detection Using Reflected Shortwave Radiation from Irrigated Corn Canopies

  1. Tracy M. Blackmer ,
  2. James S. Schepers,
  3. Gary E. Varvel and
  4. Elizabeth A. Walter-Shea
  1. D ep. of Agronomy
    U SDA-ARS
    D ep. of Agric. Meteorology, Univ. of Nebraska, Lincoln, NE 68583

Abstract

Abstract

Techniques that measure the N status of corn (Zea mays L.) can aid in management decisions that have economic and environmental implications. This study was conducted to identify reflected electromagnetic wavelengths most sensitive to detecting N deficiencies in a corn canopy with the possibility for use as a management tool. Rdlected shortwave radiation was measuredf rom an irrigated corn N response trial with four hybrids and five N rates at 0, 40, 80, 120, and 160 kg N ha−1 in 1992 and 0, 50, 100, 150, and 200 kg N ha−1 in 1993. A portable spectroradiometer was used to measure reflected radiation (400–1100 nm in 1992, 350–1050 nm in 1993) from corn canopies at approximately the R5 growth stage. Regression analyses revealed that refiected radiation near 550 and 710 nm was superior to refiected radiation near 450 or 650 nm for detecting N deficiencies. The ratio of light reflectance between 550 and 600 nm to light reflectance between 800 and 900 nm also provided sensitive detection of N stress. In 1993, an inexpensive photometricc ell, which has peak sensitivity to light centereda t 550 nm, was also used to measurer eflected radiation from a corn canopy. Photometric ceil readings correlated with relative grain yield (P < 0.001, r2 = 0.74), but more research will be required to develop procedures to account for varying daylight conditions. These results provide information needed for the development of variable-rate fertilizer N application technology.

Joint contribution of the USDA-ARS and the Nebr. Agric. Res. Div., Journal Series no. 10887.

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