World’s Soil Resources

Fukushima
Legend
(Bq kg -1 )
0 - 500
500 - 1000
1000 - 5000
5000 - 10000
10000 - 25000
25000 - 50000
50000<
Figure 10.6 Distribution map of radioactive Cs concentration in soil in Fukushima prefecture (reference date of 5 November, 2011).
Source: Takata et al., 2014.
agent to prevent scattering of contaminated soil during a topsoil removal operation. Contamination level 3
(10 000–25 000 Bq kg -1 ), which indicated a need to remove topsoil, was distributed in only the EA-20km and
DEA, with more than half (55 percent) in the EA-20km. Eighty percent of fields with contamination level 2
(5 000–10 000 Bq kg-1) were distributed in the evacuation zone, with the remaining 20 percent distributed
in the non-evacuation zone in Fukushima Prefecture. Paddy fields with contamination level 2 (2 100 ha) have
three options for decontamination: topsoil removal, fine-textured topsoil removal using water, and topsoil
burying. Upland fields, orchards, and meadows that are at contamination level 2 (1 200 ha) have two options
for decontamination: topsoil removal and topsoil burying.
Nutrient imbalance
The soil surface nitrogen (N) and phosphate (P) balance in Japanese arable land has been improving
(Mishima, Endo and Kohyama, 2010a; 2010b). These values serve as the index of the impact of arable land
on the environment and of the farm-gate balance of nutrients. The soil surface N (and P) balance is defined
as the total N (P) input (N kg ha -1 ) minus the total N (P) output (N kg ha -1 ). Chemical fertilizer application in
Japan declined continuously during the period from 1985 to 2005. The application rate of livestock manure
also peaked in 1990 and declined thereafter. Crop production, however, remained constant during this period.
Between 1985 and 2005, the surplus N and P (positive value of soil surface N balance) declined from 89.9 to 49.3
kg N ha -1 and from 153 to 105 kg P ha -1 respectively (Mishima, Endo and Kohyama, 2010a; 2010b). However, this
trend was not consistent at the regional level because organic amendment applications were largely related
to the availability and movement of livestock excreta (Mishima, Endo and Kohyama, 2010a) and to soil type
(Leon et al., 2012). High surplus P and low crop P uptake compared with N, P input for crop production could be
reduced. This limited negative environmental effects such as eutrophication of soil and water and conserved
limited P resources.
Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes
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in Asia