Direct field measurement of N2 and N2O evolution from soil

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Abstract
Summary: A gas lysimeter has been designed and used to measure directly the evolution of N2and N2O in a soil profile under field conditions. Concentrations of N2 in the soil atmosphere within the lysimeter as low as 2000–5000 p.p.m. have been achieved by flushing with N‐free gas. A flow of gas into the base of the lysimeter forms a barrier against diffusion of soil air into the lysimeter during measurements.After reducing the N2 concentration in the soil core, a low concentration of N2enriched in N‐15 is introduced. By monitoring changes in the 8 N value using a high‐precision isotope mass spectrometer, rates of N2 evolution down to 6 kg N2‐N ha−1 a−1 can be detected. N2O evolution was determined at the same time using the mass spectrometer in the single‐beam mode.