Nitrogen Equations before Their Time.

Soil scientists soon saw the potential utility of the stable isotope of nitrogen (¹⁵N) when it became widely available after the Second World War. A collaboration between a soil microbiologist (W.V. (Vic) Bartholomew) and a soil physicist (Don Kirkham) resulted in two seminal papers published in 1954 and 1955 that presented mathematical equations to calculate gross rates of nitrogen transformation processes. Probably because of the expense of ¹⁵N-labeled compounds, the time-consuming sample preparation procedures, and the scarcity of isotope ratio mass spectrometers, this work was largely uncited for nearly 35 years. Since its “re-discovery” in the late 1980s, the 1954 Kirkham and Bartholomew article has received more than 500 citations and been the impetus for enhancing our views on how nitrogen is turned over in soils.