CHANGES AND SIGNIFICANCE IN NATURAL 15N ABUNDANCE IN RESIDUAL NITROGEN FERTILIZER STUDIES

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Abstract
The systematic decline in δa15N (per mill 15N excess) of plant material with application of fertilizer under field conditions was verified in a growth chamber experiment with soil columns. The δa15N of NO3−-N in the zones of the high NO3−-N accululation was lower than that of the soil-derived NO3−-N but not necessarily lower than the δa15N of the fertilizer material as was the case in previously reported field experiments. Calculation of the fate of the fertilizer N based on the principle of isotopic dilution provided semi-quantitative estimates of the added N found in the plant, the soil, and the leachate.