Wind Erosion of Agricultural Soils and the Carbon Cycle - Soil Carbon: Science, Management and Policy for Multiple Benefits - page 163

Even at the landscape scale, C losses by
wind erosion are not balanced, because
sorting effects cause the transport of the
finer and lighter fractions over long distances
and its deposition at much larger areas than
the eroded sites. Buschiazzo et al . (1991)
found that the organic carbon contents of
cultivated soils were significantly different
from those of virgin soils and the A-horizon's
thickness decreased on average by 7 cm. Car-
bon losses of 33- 57% of the original soil
were measured by Zach et al . (2006) within
12-18 years of continuous cultivation. The
aggregate size distribution, as well as the par-
ticle composition, is also affected by land use.
Aggregates are destroyed by tillage, and fine
particles are blown out by wind erosion,
which lowers the carbon and nitrogen con-
tents in soils (Mendez et al ., 2006). Concomi-
tant reduction in aggregate stability might
further lead to a positive feedback for wind
erosion by increasing the soil erodibility.
Difficulties arise from balancing the
contribution of wind erosion to other soil
organic carbon (SOC)-reducing processes.
The easiest way is to trap and analyse the
eroded material directly at the field and to
calculate the soil and SOC losses. The two
most popular systems to sample aeolian
sediment are the so-called Big Spring num-
ber height (BSNE; Fryrear, 1986) and the
modified Wilson and Cook samplers
(MWAC; Kuntze et al ., 1990). Both sam-
plers are highly effective to quantify wind
erosion in the field (Mendez et al ., 2011).
For balancing soil losses or gains on a meas-
uring field of about 1 ha, a certain number
of samplers are needed. Sterk and Stein
(1997) used 21 samplers on a field of
0.24 ha, Funk et al . (2004) 15 samplers on
2.25 ha and Visser et al . (2004) 17 samplers
on a 1.6 ha field in regular and irregular
grids. This sampler density is necessary to
derive important sediment transportation
parameters as a function of the distance,
like the vertical flux density, the particle
composition and the SOC content, and to
calculate the final soil loss (Funk et al .,
2004). Based on 15 years of wind erosion
measurements on sandy soils (SOC 0.9%)
in north-eastern Germany, Funk (2013, un-
published) calculated an average SOC loss

of 117 kg ha − 1 . This is far above the limit
value of 75 kg ha − 1 according to good man-
agement practice in the 'Cross Compliance'
regulations of the EU (EU, 2009).
The nutrient content of the emitted
dust is greater than the original soil, with
significantly higher available phosphorus (P),
nitrogen (N) and organic matter contents
(Ramsperger et al ., 1998; Hoffmann et al .,
2008a). Buschiazzo et al . (2007) have meas-
ured enrichment ratios of 2-5 for N and of
1.5- 8 for P for dust transported at heights of
0.13 and 1.5 m, respectively. Funk (1995)
estimated an enrichment ratio of about 8 for
the SOC content of eroded soil material
from a sandy soil, measured at heights of
1 and 6 m. Measurements in Niger by Sterk
et al . (1996) showed 17× higher contents of
potassium (K), C, N and P in the dust,
trapped at a height of 2 m, compared to the
topsoil. The remaining sediments on the
eroded field or at its leeward boundary have
a distinctly lower content of nutrients and
SOC, easily detectable by the much lighter
colour.
Additional information on the effect of
wind erosion on SOC stocks is available
from indirect measurements, but methods
balancing the SOC stocks and turnover
rates are more complex and have to con-
sider periods of more than 10 years (Kolbe,
2010). For example, Buschiazzo and Taylor
(1993) compared, in the semi-arid Pampas
of Argentina, heavy and lightly eroded soils
after many years of contrasting management
systems and concluded that eroded soils
lost 25- 35% of their original SOC contents.
At a long-term monitoring site in northern
Germany, SOC losses of 25 t ha − 1 could be
assigned to wind erosion, reducing the SOC
content from 2.5% in 1990 to 1.8% in 2009
(−28%). Differences in the SOC stocks that
could not be explained by the balance
method of Kolbe (2010) were most likely
caused by wind erosion.

Physics of the Processes

Generally, in comparison to other soil-
degrading processes, the availability of reli-
able data of wind erosion effects on the SOC