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This article in AJ

  1. Vol. 72 No. 5, p. 789-792
    Received: Sept 26, 1979

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Gaseous N Losses from Winter Wheat1

  1. M. L. Hooker,
  2. D. H. Sander,
  3. G. A. Peterson and
  4. L. A. Daigger2



Research monitoring N uptake by various agricultural crops has shown total N accumulations in the plant to increase prior to the growth stages around heading to flowering with a subsequent decrease in total N occurring after flowering. Volatilization of N from the plant may account for much of this loss as well as account for some of the deficits exhibited in N balance studies. Experiments were conducted in a gas-tight growth chamber to determine what role plants alone may play in the overall loss of N from the soil-plant system. Winter wheat (Triticum aestivum L.) was established, vernalized, and grown to maturity in the growth chamber. At first internode elongation, the chamber was closed and sealed for the duration of the experiment. Air supplied to the chamber during this period was bubbled through 1 N H2SO4 to remove ambient NH3 and through a reagent specific to NO and NO2 to remove these gases. Air samples were continuously drawn from the chamber and bubbled through 0.2 N H2SO4 to trap evolved NH3. These samples were collected weekly and analyzed using steam distillation. A second portion of the air sample was washed through the NO-NO2 specific reagent and analyzed colorimetrically. Only trace amounts of NO and NO2 could be found at any time during the experiment leading to the conclusion that volatilization of these gases does not contribute significantly to the loss of N from the plant. Ammonia volatilized from the system at the rate of 0.34 to 0.89 ✕ 10−1 mg NH3-N/m2/day prior to flowering. After flowering the rate of NH3-N evolution increased to 1.03 to 1.32 ✕ 10−1 mg/m2/day. This dramatic increase in the rate of NH3-N evolution at flowering coincides with the plant growth stage that researchers have begun to observe deficits in total N accumulations in the above ground portion of the plants. This data supports the hypothesis forwarded here, that volatilization of NH3 from plant tissue can partially account for the deficits in total N accumulation observed in plant tissue following flowering.

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