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This article in SSSAJ

  1. Vol. 50 No. 6, p. 1478-1483
     
    Received: Sept 26, 1985


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doi:10.2136/sssaj1986.03615995005000060020x

Nitrogen Mineralization Kinetics with Different Soil Pretreatments and Cropping Histories1

  1. E. G. Beauchamp,
  2. W. D. Reynolds,
  3. D. Brasche-Villeneuve and
  4. K. Kirby2

Abstract

Abstract

A laboratory study was conducted to determine how soil pretreatment (air-drying, freezing, and field-moist) and cropping history affects the kinetics of N mineralization. Although most researchers suggest that net N mineralization behaves according to first order kinetics, some have suggested that this process is better described with zero order kinetics. It was hypothesized that the air-drying pretreatment may be largely responsible for an N mineralization pattern which may be described by first order kinetics. Experimental data showed that net N mineralization followed a first order kinetics pattern regardless of pretreatment. However, the air-drying pretreatment enhanced N mineralization during the first 7 d of incubation. The traditionally used first order kinetics model (Model I) was extended to take into account an “easily” mineralized N fraction (Ne) mostly released during the first 7 d of incubation. This amended model (Model II) generally provided a much better fit to the experimental data, especially for the air-drying pretreatment. As a result of the flush of mineralized N during the first 7 d, the total quantity of N released with air-drying was considerably greater than with the freezing or field-moist pretreatments. Organic N was released in a linear manner over the 42-d incubation period and comprised about 10% of the total N released. Since this organic N would probably be mineralized, the total N leached was used to determine mineralizable N values (No) and rate constants (k). Mineralizable N values for bromegrass (Bromus inermis) and alfalfa (Medicago sativum) soils were generally higher than those for corn (Zea mays L.) whereas cropping history had no apparent effect on the k value. There were no significant effects of soil pretreatment on No or k values produced with Model II whereas differences occurred with Model I.

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