World’s Soil Resources

Figure 10.5 Indonesian peatland map overlaid with land cover map as of 2011. Source: Wahyunto et al., 2014.
10.5.3 | Case study for Japan
The islands which make up Japan are located in the one of the most active parts of the Circum-Pacific Ring
of Fire. The major islands are Hokkaido, Honshu, Shikoku and Kyushu. There are 110 active volcanoes in Japan
(16 volcanoes in Hokkaido, 38 volcanoes in Honshu and 11 volcanoes in Kyushu). Large quantities of tephras
from volcanoes have been deposited on the Pleistocene terraces, constituting a main parent material of
Japanese soil (Andosols). Japan’s total land area is about 378 000 km 2 . About 72 percent of Japan’s land area is
mountainous, and rivers are characterized by their steep gradients and relatively short lengths. About twothirds
of the total land area consists of forest. The plains cover only about 28 percent of the total land area.
Most plains are located along the seacoast. Arable lands account for 12.1 percent of the total land surface,
mainly distributed in the plains. The climate of Japan is influenced by a monsoonal flow that carries moist air
from the Indian Ocean and Pacific Ocean. In general, Japan has four distinct seasons: spring (March to May),
summer (June to August), autumn (September to November) and winter (December to February).
Japan’s arable land covers 4.5 million ha, with paddy fields accounting for just over half the area (54 percent).
Grey lowland soils (Fluvic Hydragric Anthrosols or Gleyic Fluvisols (FAO/IUSS/ISRIC, 2006) comprise the largest
cultivated soil area; followed by Gley soils (Gleyic Fluvisols), Andosols (Aluandic or Silandic Andosols), Brown
forest soils (Haplic Cambisols), Brown lowland soils (Haplic Fluvisols), and Wet Andosols (Gleyic Andosols).
Urban sprawl and other changes in land use (including abandonment of cultivation) led to a shrinking of the
agricultural land area by about 1 million ha between 1973 and 2001. Urbanization and consequent soil sealing
advanced into flat lowland areas, largely into paddy fields on Grey Lowlands soils and Gley soils. In addition,
loss of Andosols to expanding urbanization was widely observed over the flat upland fields in the middle part of
Hunshu islands. By contrast, upland fields on steep slopes in the western part of Japan, largely on distributed
Brown Forest Soils, were simply abandoned (Takata et al., 2011b).
Soil organic carbon change
Spatio-temporal variations in soil organic carbon (SOC) content in arable land were evaluated by both
model-based (Yagasaki and Shirato, 2014) and monitoring-based (Takata, 2010) approaches. In the modelbased
approach, SOC stock change was simulated using the original Rothamsted Carbon model (Coleman
and Jenkinson, 1996) and two modified Rothamsted Carbon models (Shirato, Yagasaki and Nishida, 2011;
Takata et al., 2011a). The rate of change in the total SOC stock in Japanese agricultural lands evaluated with
10year intervals was estimated to be -0.95 Tg C yr -1 between 1980 and 1990. A greater loss of SOC, equal to -1.06
Tg C yr−1, was found subsequently for the period from 1990 to 2000.
Status of the World’s Soil Resources | Main Report Regional Assessment of Soil Changes
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in Asia