Environmental Engineering Reference
In-Depth Information
resource, its depletion rate has raised concerns. The demand for biofuels has also
increased because of the diversification of energy resources and the need to reduce
greenhouse gas emissions; hence, there is a major demand for crops such as sugar-
cane and corn as biofuel materials. The use of bioethanol is now increasing rapidly
around the world, a trend that is also affecting crop production patterns. Bioethanol
has the potential to become 'carbon-neutral' on a life cycle basis. However, grow-
ing such crops requires water and nutrients supplied by fertilizers, in addition to the
need for fossil fuels in machinery used for harvesting. In this context, the securing
of supplies of phosphorus has considerable implications that extend beyond food
and agricultural policy.
Various authors have analyzed the flow of phosphorus from both economical
use and recycling perspectives (Li et al.
2007
; Neset et al.
2008
; Matsubae-Yo-
koyama et al.
2010
). From these analyses, we might better be able to go beyond
the 'once-through mode of societal phosphorus metabolism' described by Liu et al.
(
2008
). However, it is difficult to trace the supply chain of phosphorus used in
products, because phosphorus and other plant nutrients are one of the most widely
used elements in society. This point calls for taking a bird's-eye view for a better
understanding of the flow of phosphorus including agricultural products and meat
products (Goodlass et al.
2003
).
9.3.2
Data
It was necessary to classify the flow of phosphorus by demand for this analysis.
Thus, we first evaluated the flow of phosphorus within the Japanese economy.
Second, we focused on the agricultural demand for phosphorus. The phosphorus
requirement for one unit of agricultural production was estimated on the basis of
fertilizer statistics and the lifecycle inventory data of livestock feed. Matsubae-
Yokoyama et al. (
2009
) had evaluated the phosphorus flow of Japan in 2002. We
evaluated the domestic phosphorus flow partly with reference to data from previous
studies and analyzed the agricultural and related sectors in more detail with use of
the Japanese input-output table for 2005, the food balance sheet, and other agricul-
tural statistics.
Figure
9.1
shows the substance flow for phosphorus in Japan. The flow was
estimated from the statistical data based on the above-mentioned 2005 data. To
simplify the analysis, the total phosphorus flow was evaluated by considering each
of the sectors shown in the flow and the total mass balance. Although there are other
much smaller input and output flows, we omitted those with values smaller than
10 kt from the figure.
The Material Flow Analysis (MFA) reveals estimates of the domestic stock and
flow of phosphorus in Japan. The total input of phosphorus into Japan is estimated
to be 616 kt. Of this input, 40 % (251.1 kt) is used in fertilizers and 26 % (163.1 kt)
is consumed by humans and livestock; the phosphorus through both routes finally
ends up in either soil or water. In addition, 16 % (100.5 kt) phosphorus is utilized in
