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This article in AJ

  1. Vol. 103 No. 2, p. 422-430
    Received: Apr 7, 2010

    * Corresponding author(s): Kevin.Bronson@ars.usda.gov
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Canopy Reflectance-Based Nitrogen Management Strategies for Subsurface Drip Irrigated Cotton in the Texas High Plains

  1. Kevin F. Bronson *a,
  2. Adi Malapatib,
  3. Peter C. Scharfc and
  4. Robert L. Nicholsc
  1. a USDA-ARS, U.S. Arid Land Agric. Res. Center, Maricopa, AZ 85138
    b Texas A&M AgriLife Research, Lubbock, TX 79403
    c Univ. of Missouri-Plant Sciences, Columia, MO 65211


Nitrogen fertilizer management in subsurface drip irrigation (SDI) systems for cotton (Gossypium hirsutum L.) can be very efficient when N is injected with the irrigation water (fertigated) on a daily basis. However, the daily rates and total amounts of N fertigation are uncertain. Normalized difference vegetative index (NDVI), calculated from weekly canopy reflectance measurements can guide N management in SDI cotton. The objective of this 3-yr study (2007–2009) on an Acuff sandy clay loam (fine-loamy, mixed, superactive, thermic Aridic Paleustolls) near Lubbock, TX, was to test two canopy reflectance-based strategies for estimating and adjusting injection rates of urea ammonium nitrate (UAN) fertilizer between first square and early mid-bloom. We also evaluated three N rates; 50, 100, and 150% of the soil test-based N recommendation for a 1400 kg lint ha−1 yield goal. In the reflectance-based N strategy-1 (RN1), UAN was injected starting at first square at 50% of the soil test N rate. When NDVI in RN1 fell significantly below NDVI of plots with 100% soil test N, the N injection rate was increased to match the injection rate of the 100% soil test plots. The reflectance-based N strategy-2 (RN2) had an initial N injection rate equal to that of the 100% soil test N, and was raised to match the 150% soil test N based on NDVI. Nitrogen rates for the RN1 averaged across 3 yr were 22 kg N ha−1 less, or 31% less than the soil test treatment, without hurting lint or seed yields. In 2007, N rates with RN2 were 11 kg N ha−1 higher than the soil test N rate, without any yield benefit. Economic optimum N rates for lint production ranged from 23 kg N ha−1 in 2009 to 75 kg N ha−1 in 2008.

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