Field-scale measurements of carbon exchange
in cropping systems Flux measurements of greenhouse gases over agricultural systems provide
a picture of the processes that affect them and the influences of management
on their uptake and release. Carbon is particularly susceptible to change
when perennial systems are converted to annual agriculture, and the fluctuations
in carbon dioxide (CO2) can be measured to observe how the conversion,
seasonal management, and weather influence it. We measured CO2 exchange
using the eddy covariance method from 2009 through 2011 on three adjacent
quarter-sections at Woodlands, MB. One field was converted from pasture
in 2008, and has had an oat-canola-oat rotation since then. A second field
was converted from pasture in 2009, and had oats followed by a fallow
year due to excess moisture. A control field remained as a perennial,
timothy hay dominated pasture that has been without cultivation for more
than 20 years. Conversion caused an immediate carbon loss following tillage,
and subsequent annual crops had carbon losses when harvest removals are
accounted for compared to the perennial site, which was closer to carbon
neutrality. Moisture stresses contributed to variability among the sites,
as did weed growth after harvest, and each site showed inter-annual variability
dependent on weather, crop, and management.
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