Nitrous oxide fluxes from upland soils in central Hokkaido, Japan
MU Zhijian , Sonoko D. KIMURA , Yo TOMA , Ryusuke HATANO
DOI:
Received November 09, 2007,Revised January 07, 2008, Accepted , Available online
Volume 20,2008,Pages 1312-1322
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Nitrous oxide (N2O) fluxes from soils were measured using the closed chamber method during the snow-free seasons (middle April
to early November), for three years, in a total of 11 upland crop fields in central Hokkaido, Japan. The annual mean N2O fluxes ranged
from 2.95 to 164.17 gN/(m2 h), with the lowest observed in a grassland and the highest in an onion field. The instantaneous N2O
fluxes showed a large temporal variation with peak emissions generally occurring following fertilization and heavy rainfall events
around harvesting in autumn. No clear common factor regulating instantaneous N2O fluxes was found at any of the study sites. Instead,
instantaneous N2O fluxes at di erent sites were a ected by di erent soil variables. The cumulative N2O emissions during the study
period within each year varied from 0.15 to 7.05 kgN/hm2 for di erent sites, which accounted for 0.33% to 5.09% of the applied
fertilizer N. No obvious relationship was observed between cumulative N2O emission and applied fertilizer N rate (P > 0.4). However,
the cumulative N2O emission was significantly correlated with gross mineralized N as estimated by CO2 emissions from bare soils
divided by C/N ratios of each soil, and with soil mineral N pool (i.e., the sum of gross mineralized N and fertilizer N) (P < 0.001).
