Environmental Engineering Reference
In-Depth Information
soil characteristics, fertilizer type, fertilizer application mode, climate, strongly
influence the total amount of N
2
O efflux associated to a fertilization event. These
two important considerations, which have relevant implications for the estimated
magnitude of N
2
O emissions, cannot be taken into account by the simple application
of the general IPCC EFs.
The main limitation to improve the available estimates comes from the uneven
distribution of studies over the globe. In particular, for what concerns studies in
temperate areas, the totality of them refers to countries of central and northern
Europe, while data from Mediterranean areas are unavailable (Bouwman et al.
2002a
). Both high temperatures and relatively low rainfall regimes could strongly
affect the EFs in this region.
9.4 A Comparison of N
2
O Flux Strength Obtained Using
Specific EFs for Mediterranean Conditions, General
IPCC EFs and Empirical Modeling
In this paragraph we present a series of available data of N
2
O emissions in crop-
lands obtained during the CarboItaly project and from other studies in Italy. The
data were analyzed in order to derive an average emission factor to be compared
with those available in literature (IPCC
1997
,
2006
) or with estimates which
can be derived using simple empirical models based on published global data
(Bouwamn et al.
2002b
).
The data used were recalculated from studies listed in Table
9.1
. Most of the
sites were cultivated with maize and all of them have been continuously cultivated
in the last 20 years, so that we can therefore reasonably exclude the effect of land
use change on the measured background fluxes. The analyzed sites present differ-
ent soil managements, fertilization rates and site characteristics. At all sites N
2
O
fluxes were measured using closed static PVC chambers (Hutchinson and Mosier
1981
; Smith et al.
1995
) coupled with GC or Photoacustic analyser. Specific tech-
nical details on experimental set up and procedures can be found in the literature
cited in Table
9.1
.
At each site, the total amount of N
2
O emitted at each single fertilization event
was quantified by linear interpolation between sampling dates following the event
till the flux reached a steady value close to the pre-fertilization level. The latter
was instead defined as baseline flux and the fertilizer induced emission (FIE) was
then calculated as the difference between the total flux minus the baseline flux.
The corresponding EF was finally computed as the ratio between FIE and the
amount of N added at the considered fertilization event.
Results show that for this specific crop, with its growing season in spring-
summer, hence when the combination of temperature and rain regime mostly
differs from non Mediterranean climate areas, the calculated emission factors
were lower than the average emission factor reported by IPCC (
2006
) for tem-
perate agricultural soils (1 %) (EFs reported in Table
9.2
), with the exception of
