The Isotope Composition of Residual Fertilizer Nitrogen in Soil Columns1
- R. E. Karamanos and
- D. A. Rennie2
A growth chamber experiment was carried out in which soil coumns that had received none or 200 kg N/ha were subjected to two differing water regimes. The δa 15N (per mill 15N excess) of the NO3-N present in the leachate of all treatments decreased initially, with maximum depletion occurring between 4 and 6 weeks. In general, during the 14- to 16-week period, large increases in the δa 15N of the leachate occurred. The magnitude of the decreases and subsequent increases were least for the drier water regimes receiving no fertilizer N (δa 15N ranging from −2 to +7) and greatest for the high water fertilized treatment (δa 15N ranging from −12 to +40). This very extensive fractionation was attributed to the preferential nitrification of 14NH4+.
Isotope balance calculations based on the isotope dilution principle are included to illustrate the serious errors that can be made in estimating the fertilizer N content of selected N compartments if the NO3--N is leached before the NH4+ oxidation is completed.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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