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

Aerobic production of N2O and N-2 from denitrification in four low-fertilit y ecosystems was measured using the short-lived radioisotope N-13. The ecos ystems, 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, al though the soils were dry on all three occasions (summer, autumn and spring ) that samples were taken. Emission rates and N2O-to-N-2 ratios were genera lly highest in the surface 0-2 cm in the pasture soils, but not as frequent ly in the forest soils. Some of the forest soil samples produced a third ga s, tentatively identified as NO. Emissions of N2O, but not of N-2, appeared to be generally greater from the forest than from the pasture sites, altho ugh 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 betw een (NO3-)-N-13-N added and NO3--N present in the soil, placed these ecosys tems at the lower end of emission rates for undisturbed ecosystems, with ra tes 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)). (C) 1999 Elsevier Science Ltd. All rights reserved.