Modified Waterlogged Incubation Method for Assessing Nitrogen Mineralization in Soils and Soil Aggregates

A commonly used waterlogged incubation method for measuring mineralizable N was modified to decrease analysis time and increase sample precision by eliminating the sample transfer step. The modified method was tested for speed, ease of use, susceptibility to error, NH + 4 recovery, and precision. Modifications included (i) use of a 60‐cm 3 polypropylene syringe as the incubation vessel rather than a glass test tube, and (ii) KCl extraction of sample NH + 4 within the syringe and colorimetric determination of N rather than sample transfer to an extraction flask and subsequent N analysis. The syringe modification reduced sample setup and extraction time by one‐third while significantly increasing analysis precision. Net NH + 4 production in the syringe compared favorably with that in the standard test tube when a 1‐h shake extraction was employed. The potential for error due to NO ‐ 3 reduction to NH + 4 via a dissimilatory NO ‐ 3 reduction pathway was quantified with 15 N. Of the 21 mg N kg ‐1 of 15 N‐labeled KNO 3 added prior to incubation, 14% was reduced to NH + 4 , corresponding to a 5% error in the measurement of mineralizable N.