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CH 4 and N 2 O fluxes in the Colorado shortgrass steppe: 2. Long‐term impact of land use change
Author(s) -
Mosier A. R.,
Parton W. J.,
Valentine D. W.,
Ojima D. S.,
Schimel D. S.,
Heinemeyer O.
Publication year - 1997
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1029/96gb03612
Subject(s) - grassland , steppe , conservation reserve program , plough , environmental science , agronomy , nitrous oxide , soil water , zoology , chemistry , ecology , soil science , biology , agriculture
As part of a weekly, year‐round program to measure the soil‐atmosphere exchange of nitrous oxide (N 2 O) and methane (CH 4 ) in a shortgrass steppe, we examined the impact of land use change on these fluxes from 1992 through 1995. We found that conversion of grassland to croplands typically decreased the soil consumption of atmospheric CH 4 and increased the emission of N 2 O. Mean annual CH 4 consumption and N 2 O efflux over 3 years in native grasslands were 35 µg C m −2 hr −1 and 1.9 µg N m −2 hr −1 , respectively. Immediately after tilling a native grassland site, CH 4 consumption decreased by about 35% and remained at these lower rates for the next 3 years. Although N 2 O fluxes were about 8 times higher for 18 months following plowing, the relative rates declined to 25–50% higher than the native site after 3 years. Grasslands converted to a winter wheat‐fallow production system about 70 years ago consumed about 25% less CH 4 than a newly plowed site, while N 2 O emissions 2 years after plowing were similar to the wheat fields. During the fallow periods when soils were typically wetter and mineralized N accumulated, CH 4 uptake rates were lower and N 2 O emissions were higher than the correspondingly active wheat fields. A wheat field that was reverted back to grassland in 1987 through the conservation reserve program (CRP) continued to exhibit annual CH 4 uptake and N 2 O emission rates similar to the wheat fields. Winter N 2 O emissions were, however, much higher in the CRP because of greater snow accumulation and winter denitrification events. Another wheat field that was returned to grassland in 1939 exhibited the same CH 4 and N 2 O flux rates as comparable native pastures.