Short-lived isotopic method to measure nitrous oxide emissions from a soil under four low-fertility management systems

Aerobic production of N2O and N2 from denitrification in four low-fertility ecosystems was measured using the short-lived radioisotope 13N. The ecosystems, comprising two pastures, native beech (Nothofagus truncata) forest and exotic pine (Pinus radiata) forest, all had the same soil and the same slope and aspect. There was no consistent seasonal pattern of emissions, although the soils were dry on all three occasions (summer, autumn and spring) that samples were taken. Emission rates and N2O-to-N2 ratios were generally highest in the surface 0–2 cm in the pasture soils, but not as frequently in the forest soils. Some of the forest soil samples produced a third gas, tentatively identified as NO. Emissions of N2O, but not of N2, appeared to be generally greater from the forest than from the pasture sites, although only a limited number of samples were studied. Nitrate–N concentrations were generally low (ranging from 0.36 to 57.4 mg kg−1, mean 3.27 mg kg−1) in these samples. Production of N2O, estimated from the relativity between 13NO−3–N added and NO−3–N present in the soil, placed these ecosystems at the lower end of emission rates for undisturbed ecosystems, with rates ranging from 0.02 to 6.38 ng N2O–N g−1 soil h−1 (mean 0.65 ng N2O–N g−1 soil h−1).