The management of agroecosystems plays a crucial role in the global carbon
cycle with soil tillage leading to known organic carbon redistributions
within soils and changes in soil CO2 emissions. Yet, discrepancies exist
on the impact of tillage on soil CO2 emissions and on the main soil and
environmental controls. A meta-analysis was conducted using 46 peer-reviewed
publications totaling 174 paired observations comparing CO2 emissions
over entire seasons or years from tilled and untilled soils across different
climates, crop types and soil conditions with the objective of quantifying
tillage impact on CO2 emissions and assessing the main controls. On
average, tilled soils emitted 21 % more CO2 than untilled soils,
which corresponded to a significant difference at P<0.05. The
difference increased to 29 % in sandy soils from arid climates with low
soil organic carbon content (SOCC < 1 %) and low soil
moisture, but tillage had no impact on CO2 fluxes in clayey soils with
high background SOCC (> 3 %). Finally, nitrogen
fertilization and crop residue management had little effect on the CO2
responses of soils to no-tillage. These results suggest no-tillage is an
effective mitigation measure of carbon dioxide losses from dry land soils.
They emphasize the importance of including information on soil factors such
as texture, aggregate stability and organic carbon content in global models
of the carbon cycle
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