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This article in AJ

  1. Vol. 97 No. 3, p. 698-704
    Received: Mar 25, 2004

    * Corresponding author(s): j.sheehy@cgiar.org


Temporal Origin of Nitrogen in the Grain of Tropical Wet-Season Rice

  1. J. E. Sheehy *a,
  2. M. Mnzavaa,
  3. K. G. Cassmanb,
  4. P. L. Mitchellc,
  5. A. B. Ferrera,
  6. R. P. Roblesd and
  7. P. Pablicoa
  1. a IRRI, DAPO 7777, Metro Manila, Philippines
    b Dep. of Agronomy and Horticulture, Univ. of Nebraska, Lincoln, NE 68583
    c Dep. of Animal and Plant Sciences, Univ. of Sheffield, Sheffield S10 2TN, UK
    d Dep. of Agronomy, Univ. of the Philippines, Los Baños, Philippines


The total N in the grain is the integral of the product of the total N absorbed at any instant and the fraction of that N eventually allocated to the grain. We investigated the temporal origin of N in the grain of a wet season rice crop and tested the suitability of 15N nitrate (NH4 15NO3) as a label for that purpose. The total N content of rice (Oryza sativa L.) plants was measured by growth analysis throughout the duration of the crop and the measurements were used to calculate the rate of total N uptake. A point-placement technique was used to deliver small amounts of 15N nitrate to roots of the rice plant and this enabled the eventual fate of the total N absorbed at any time to be determined. The rate at which N was acquired by the panicle exceeded that by the whole plant at 64 d after transplanting (DAT); thereafter, N was transferred from the leaves to the panicle. About 60% of N in the grain was acquired before panicle initiation and was transferred from leaves during grain filling. A comparison between the uptake and retention of labeled nitrate and urea applied separately at 35 DAT showed that 21 and 58% of the 15N nitrate and 15N urea, respectively, were recovered. There were no advantages of using 15N nitrate as opposed to 15N urea as a label in such research of irrigated rice.

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