Page 249 - Environment: The Science Behind the Stories

THe SCIeNCe BeHIND THe SToRy

Can No-Till Farming was no significant difference among
Help Us Fight the plots—and thus no evidence for
the offsetting hypothesis. They also
Climate Change? found that plots of mature forest that
had never been cleared for agriculture
As concern over global climate change held more carbon than either type of
has grown, many agricultural scien- cropped plot.
tists have touted no-till farming as one In Georgia, Scott Devine and three
part of the solution. Climate change colleagues dug 2 meters deep and
(Chapter 18) is driven by our emission analyzed soil samples from long-term
of greenhouse gases, such as carbon experimental fields at a site in Athens
dioxide, which warm the atmosphere. called Horseshoe Bend. Working with
Because no-till farming reduces soil data collected yearly since 1982, they
disturbance, proponents argue that it found that no-till plots contained sig-
returns crop residue to the soil faster nificantly more carbon in the topmost
than soil organisms decompose such soil layer (0–5 cm depth), but that each
organic matter and emit carbon dioxide Technician taking a soil sample, layer below that showed no significant
by respiration (p. 50). In this way, the Columbus, Ohio. difference between plowed and no-till
argument goes, no-till farming could plots (Figure 1). In 2011 they reported
serve as one method of carbon seques- that, overall, no-till plots and forested
tration or carbon storage (pp. 526, 555). from conventional plowing to no-till land held 20% more carbon than con-
An avalanche of research papers farming would reduce emissions by ventionally plowed land.
shows that no-till methods increase soil 30–35 kg C/ha per season. Yet in
organic carbon (SOC) in the topsoil, 2008, Lal and colleague Humberto
and some policymakers were becoming Blanco-Canqui analyzed soil samples 0
persuaded that polluters should begin down to 60 cm (2 ft) on farms in Ohio,
paying no-till farmers in carbon-trading Pennsylvania, and Kentucky, and they
markets (pp. 530–531) to offset the pol- concluded that no-till fields often have 50 At shallow depths,
luters’ emissions. less carbon at deeper levels than con- plots vary in carbon
content
Then some researchers began to ventionally plowed fields.
dig deeper. Literally. A number of soil Were no-till farming’s carbon gains At deeper depths,
scientists noticed that very few studies in the topsoil, then, offset by carbon Depth (cm) 100 plots have equivalent
were measuring the organic matter in losses deeper in the soil profile? Many carbon content
soil below a depth of 30 cm (1 foot). researchers began testing this hypoth-
Yet SOC makes its way downward esis. Among them were researchers 150 Conventional till
over time, and many crop plants’ roots in Michigan and in Georgia who took No-till
reach deeper than this. These scientists advantage of long-term research pro- Forest succession
wondered whether no-till farming was grams at university-run sites. 200
increasing SOC at deeper levels in the At the W.K. Kellogg Biological 0 5 10 15 20
soil. If not, then we’d better invest our Station in Michigan, S.P. Syswerda Total SOC (g/kg of soil)
efforts elsewhere in the urgent search and four colleagues took soil sam-
for climate change solutions. ples down to 1 meter in depth from Figure 1 in a georgia study, no-till plots
One researcher to raise ques- experimental farm plots established in contained more carbon in the topsoil than
tions was Rattan Lal of The Ohio State 1988. They reported in 2011 that plots conventionally plowed plots, while for-
ested plots had the most. At deeper soil
University. Lal had been one of the under no-till farming (as well as plots levels, there was no significant difference.
foremost promoters of the idea that under organic farming (pp. 275–278) Data from Devine, Scott, et al., 2011. Soil carbon
farmers could help fight climate change held significantly more carbon at shal- change through 2 m during forest succession
by using conservation tillage. In a 2004 low depths than did conventionally alongside a 30-year agroecosystem experiment.
paper, Lal calculated that converting plowed plots. At lower depths, there Forest Science 57: 36–50.

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