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This article in JEQ

  1. Vol. 31 No. 3, p. 759-768
     
    Received: Oct 10, 2000


    * Corresponding author(s): jmscholberg@mail.ifas.ufl.edu
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doi:10.2134/jeq2002.7590

Soil Temperature, Nitrogen Concentration, and Residence Time Affect Nitrogen Uptake Efficiency in Citrus

  1. J. M. S. Scholberg *a,
  2. L. R. Parsonsb,
  3. T. A. Wheatonb,
  4. B. L. McNealc and
  5. K. T. Morganb
  1. a Agronomy Dep., 304 Newell Hall, Univ. of Florida, Gainesville, FL 32611
    b Univ. of Florida, Citrus Res. and Educ. Center, 700 Experiment Station Road, Lake Alfred, FL 33850
    c Soil and Water Science Dep., Univ. of Florida, IFAS, Gainesville, FL 32611

Abstract

We try to elucidate which environmental and soil factors control nitrogen uptake efficiency in citrus. Effects of residence time and nitrogen (N) concentration (three 500-mL applications of 7 mg N L−1, representative of reclaimed water used for citrus irrigation in central Florida, or one 150-mL application of 70 mg N L−1) on nitrogen uptake efficiency (NUE) of young citrus seedlings were studied. Increasing residence times from 2 to 8 h increased NUE from 36 to 82% and from 17 to 34% for high and low application frequencies, respectively. We developed a model to predict N uptake based on root density, N concentration, and soil temperature (T s). Assuming a base temperature (T b) of 10°C, N uptake temperature sum (UTS) = ∑(T sT b)/24 (°CdN, degree day units of N uptake). To eliminate the risk of N leaching for young seedlings, minimum uptake periods of 5 and 16°CdN were required at initial soil N concentrations of 0.9 and 2.5 mg N L−1, respectively. After correcting for differences in root length, this information was then used to predict the effect of irrigation practices on N uptake from reclaimed water for mature trees. Applying 2500 mm yr−1 vs. 400 mm yr−1 reclaimed water reduced the NUE of N in this water from 100 to 63% during the summer and from 100 to 28% during the winter. Reductions in NUE at higher irrigation rates appeared to be related to N displacement below the root zone prior to complete N uptake.

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Copyright © 2002. American Society of Agronomy, Crop Science Society of America, Soil Science SocietyPublished in J. Environ. Qual.31:759–768.