N-15 isotope dilution techniques to study soil nitrogen transformations and plant uptake

The use of N-15 as a tracer in soil/plant research is examined. The limitations of the so-called Ndff approach are discussed to show the need to consider not just the fate of the added label but also the path that was followed and the rate of the transformation. The development of N-15 isotope dilution techniques to determine gross rates of nitrogen transformation in soil is reviewed with some indications as to the further development of the approach.