Page 250 - Environment: The Science Behind the Stories

Meanwhile, researchers in Brazil— becoming clear. One is that natural
where no-till farming is widespread ecosystems sequester more carbon Convert annual row
crops to forests
and has boosted crop yields—were than croplands; forests in eastern
doing similar experiments and find- North America, for instance, store a Restore prairie
ing that no-till was increasing carbon great deal of carbon in their veg- potholes
storage at both shallow and deeper etation and their humus-rich soil. Convert annual row
depths. Robert Boddey and 12 col- Another is that no-till farming is not crops to perennial
leagues from Brazilian universities grassland
studied three sites in southern Brazil
Include cover crops
running long-term (15- to 26-year) in row-crop rotation
farming experiments. They reported We can take various
in 2010 that sampling soil down to At shallow depths, conventionally Convert annual row actions in agriculture
that could sequester
100 cm reveals no-till methods stor- plowed plots lost more carbon crops to pasture far more carbon than
relative to natural soils than
ing 59% more carbon than is evident no-till plots did converting to no-till
farming
when sampling extends to only 30 cm. Convert conventionally
plowed land to
Boddey maintains that in warm sub- 0 conservation tillage
tropical regions with a lot of rain and 5 (n=15)
well-drained soils, carbon makes its (n=13) 0 2 4
way downward in the soil profile more 10 Carbon sequestration
rate (Mg C/ha/yr)
easily. As a result, whereas shallow 15
sampling in the temperate zone tends 20 (n=10) Figure 3 Converting to conservation
to overestimate the carbon-storage tillage ranks low among actions we can
benefits of no-till farming, shallow 25 take in agriculture to sequester carbon to
sampling in the tropics may underesti- Soil depth (cm) 30 fight climate change, based on a review
mate its benefits. of studies from the Midwest. Adapted from
When many studies show a 35 Fissore, Cinzia, et al., 2010. Limited potential for
diversity of results, it can be helpful 40 (n=12) terrestrial carbon sequestration to offset fossil-fuel
emissions in the upper Midwestern U.S. Frontiers
to perform a meta-analysis, a statisti- in Ecology and the Environment 8: 409–413.
cal analysis of the results of numerous 45
studies, using each one’s results as a 50
single data point. Meta-analyses look 55 Conventionally (n=9)
plowed
for trends and patterns across entire No-till a major solution to climate change
fields of research in order to clarify the 60 (Figure 3); it does help store carbon,
big picture. –16 –12 –8 –4 0 4 but not nearly enough to compensate
Mean difference of
One meta-analysis in 2010 by soil carbon stock (tons/ha) for the amounts we pump into the
Chinese and Australian researchers atmosphere by burning fossil fuels.
summarized the relative amounts of Figure 2 in a meta-analysis of 69 stud- A 2010 analysis by Cinzia Fissore
carbon at different levels in the soil of ies, more soil carbon was lost in conven- and other University of Minnesota
no-till, plowed, and unfarmed for- tionally plowed plots than in no-till plots researchers calculated that at most,
est plots, as measured by 69 studies in the topsoil layer (compared to adjacent the U.S. Midwest could offset 2% of
across the world (Figure 2). Another natural soils, indicated by a vertical dotted its region’s emissions by switching
line at the value of zero). At lower depths,
meta-analysis, by Colorado research- there were no significant differences completely to no-till agriculture.
ers in 2011, developed maps predict- between no-till and conventional plots. Data No-till farming does help lessen
ing what changes in carbon storage from Luo, Zhongkui, et al., 2010. Can no-tillage fossil fuel combustion by reducing
various areas in the United States stimulate carbon sequestration in agricultural soils? tractor use. Still, scientific research on CHAPTER 9 • So I l AN d A gr I culT ure
would experience if they switched to A meta-analysis of paired experiments. Agriculture, soil and farming methods is showing
no-till farming. Ecosystems, and Environment 139: 224–231. that to address global climate change,
Through the hard work of many Which type of plot has more carbon we had better look elsewhere for major
soil scientists, some things are content at a depth of 40 cm? solutions.

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