The Soils of Japan

This chapter provides the overview of soil types, land uses, and land managements of Japan. The soils of Japan are immature soils developed from the flesh parent materials such as volcanic tephra or ejecta or eroded or deposited materials in various landscapes from mountain terrain to alluvial plains within about 10,000 years. Japanese soils are generally acidic, since the basic cations of soils are leached by the high precipitation of the monsoon climate. According to the soil classification system of Japan newly developed in 2017, Brown Forest soils, Andosols, Fluvic soils, Red-Yellow soils, and Regosols cover 33.2, 30.3, 13.7, 7.6, and 6.9% of the country, respectively. In land uses of Japan in 2016, forests occupy 63.5% of the total land area of Japan (37.8 million ha). Cultivated land area was 4.47 million ha, which accounts for 12.0%. However, the cultivated land area has continuously decreased from 6.08 million ha in 1961. In Japan, from 1959 to 1978, the Fundamental Soil Survey for Soil Fertility Conservation was carried out and classified the crop production potential of cultivated land soils into four grades. Based on the results of the soil survey, field improvements have been performed to ameliorate the limiting factors for crop production. This has made it possible to set the fertilization standards for each crop in each region. The fertilization standards are defined as the amount of fertilizer that achieves the target yield without causing environmental issues and are the bases of the environmentally friendly agriculture. Based on the efforts in each region, in 1999, Japanese government enacted the Act on Promotion of Introduction of Sustainable Agricultural Production Practices.

Because the current climate zone of Japan ranges from subtropical to subarctic, soil temperature regime also varies from hyperthermic to frigid. The annual precipitation ranges from less than 1000 to over 2500 mm. The Pleistocene climate also affected the development of soils of Japan through formation and deposition of soil parent materials. The outline of the landforms has mainly been formed by the subduction of the tectonic plates in the vicinity, leading to a long and complicated history of the geology. The Japanese Islands constitute the most prominent volcanic area in the world with more than 111 active volcanoes. The plains are divided into the coastal plains and the inland mountain basin. A wide range of wind-blown dust, including Kosa, has been added to various sediments. The vegetation is characterized by a large number of species and a high percentage of endemic species due to a large variation in landscape, geology and climate. The majority of mountainous, hilly and volcanic areas are covered with forests. Most agricultural lands in cities situated in flat areas and suburban alluvial lowlands are mainly used for paddy fields, and higher terraces are used for upland cultivation.

The Japanese Society of Pedology released the “Soil Classification System of Japan,” the latest version of the comprehensive soil classification system in Japan. According to this classification system, the area of each soil group is calculated and soil map is produced. Andosols are found along volcanic areas, Brown Forest soils and Cambic Red-Yellow soils (refer to Cambisols) are distributed in steep mountainous zones far from active volcanoes, and Fluvic soils cover narrow lowlands. Cultivated land accounts for 12% of the total land surface and is mainly distributed in the plains. Thus, Fluvic soils show the largest distribution area (47%), followed by Andosols (29%) in the cultivated land. Nutrient imbalance, soil organic matter decline, heavy metal contamination, and soil sealing are major threats to Japanese agricultural soils.

This chapter presents the genesis, characteristics, classification, distribution, and land uses of the 10 soil grade groups (Human-made soils, Organic soils, Andosols, Podzols, Fluvic soils, Red-Yellow soils, Stagnic soils, Eutrosols, Brown Forest soils, and Regosols) in the Soil Classification System of Japan. Human-made soils are referred to soils formed through an anthropogenic process, especially in anthropized areas such as urban, industrial, traffic, mining, and waste disposal areas. Organic soils are formed under wetland conditions where the rate of organic matter production exceeds the rate of organic matter decomposition. Andosols are mainly derived from volcanic ejecta or tephra and form during a long period of pedogenetic soil formation process have unique and distinctive properties among soils, such as their fluffy and light surface properties, high humus content, and very high phosphorus-fixing capacity. Podzols are characterized by the eluviation of aluminum (Al) and iron (Fe) from the albic E horizon and their illuviation in the spodic B (Bs) horizon. Fluvic soils are young soils developed from recent alluvial deposits. Red-Yellow soils are a red or yellow color, low accumulation of organic matter, low base saturation, and strong weathering. Stagnogley soils are distributed in terraces, hills, and mountainous areas having a shallow groundwater table. Eutrosols are characterized by high base saturation, that is, with a eutric condition. Brown Forest soils are relatively young soils, are widely distributed in a rather wide range of temperate, and warm temperate zones in humid (high precipitation) climates without fresh volcanic ash deposition. Regosols are very weak weathering soils, which are divided into four groups: Volcanogenous Regosols, Sandy Regosols, Lithosols, and Terrestrial Regosols.

Hokkaido, the northernmost island in Japan, is located on the border between temperate and subarctic zones. Dominant soils distributed in Hokkaido have a wide variety such as Andosols, Fluvic soils, Brown Forest soils, and Peat soils. Paddy, upland, vegetable, dairy farming, and animal husbandry are being practiced on large scales according to the characteristics of soils and weather conditions in each region. The goal of agriculture style in Hokkaido is environmentally friendly agriculture. It can sustainably produce safe, high-quality, and high-yield agricultural products in harmony with the regional and global environments. To promote the environmentally friendly agriculture, soil fertility management techniques based on fertilization standards and soil diagnosis have been developed, with considering nutrient supply derived from applied organic matter. It has been demonstrated that practicing these techniques makes it possible to minimize the environmental impact such as nutrient leaching and greenhouse gas emissions from agricultural lands.

The Tohoku region is about 210 km east to west and 510 km north to south, with the Ohu Mountains and the Nasu Volcanic in the central area, the Kitakami and Abukuma Mountains on the east, and the Dewa Mountains and Chokai Volcano on the west. Therefore, because the Sea of Japan side and the Pacific side is divided into the mountainous backbone, the soil and the climate are very different. The soil is widely distributed in fertile soil based on tuff on the Japan Seaside. In the northern part of the Pacific Ocean, volcanic ash soil (Andosols) is distributed, and in the southern part, soil consisting of granite is distributed. In the Tohoku region, while overcoming cold and snow damage, paddy farming centered on rice farming, livestock farming using rich feed resources in the middle and mountain areas, resource crops utilizing the cool climate, production of vegetables and fruits, etc. A variety of agriculture has been developed and played a role as a food supply base for Japan. In the future, as agriculture becomes more internationalized, people’s interest in the stable supply of safe and secure food and environmental conservation will be further heightened. Under such circumstances, Tohoku agriculture is strongly required to switch to a combined system combining field crops such as wheat, soybeans, vegetables, flowers, etc. with livestock, and to expand the scale of management, while putting rice farming on a basic basis. The labor-saving and low-cost production of high-quality, and high-value-added agricultural products that meet safety needs, stable production of food by overcoming weather disasters, development of natural circulation agriculture in harmony with the environment, promotion of technology development that responds to agriculture, etc. are being carried out.

The area of Kanto-Koushinetsu occupies 16% (63,041 km²) of the land area of Japan. This region includes the Tokyo metropolis and the prefectures of Ibaraki, Tochigi, Gunma, Saitama, Chiba, Kanagawa, Yamanashi, Nagano, Niigata. Significant depletion in agricultural land has been progressed from 1972 to 2011 due to the population concentration in the urban area of Tokyo metropolis and the prefectures of Saitama, Chiba, Kanagawa. The area around the population concentration zone plays an important role in supplying vegetables, and the national share of items is 33.8% for vegetables and 25.6% for a flowering plant, and these values are the top of the Japan. In the Kanto region, the plain area occupies a large area, and agricultural activities are being developed under good water use and the existence of a populated area. The characteristics of geology, topography, climatic conditions and soil characteristics and the effects of volcanic ash soil in this area are described. The relationship between the recent agricultural production of Kanto-Koshinetsu area and the soil characteristics of each area was clarified. On the other hand, anthropogenic soils are increasing in Tokyo metropolis and problems in current soil classification system emerged from these soils has been pointed out. As a topic, an action on restoration of habitat for the reintroduction of the crested ibis in Sado Island (Sado City, Niigata Prefecture) for selected as Globally Important Agricultural Heritage System (GIAHS) was introduced. Furthermore, examples of agricultural production and soil environment conservation were introduced.

This chapter presents characteristics of soils of the Chubu region, which encompasses between the Sea of Japan and the Pacific Ocean in the middle of Honshu. In the region, there is Mt. Fuji, the active volcano and the highest mountain in Japan. Not only that, the geology of the region is diverse. The region has several mountain ranges, diverse climates and vegetation. So, you can see a lot of different type of soils in the region. In this chapter, we will first give an overview of the soil formation factors and the existing soils in the region. The chapter then describes the agriculture and forestry for the three distinct regions of the Chubu region. The northern part of the Chubu region, called Hokuriku, centers on paddy production on wet and clayey soil by virtue of snow-meltwater and summer high temperature. For the central part of the Chubu region consisting of highland, the sustainable soil management for forestry is described. As for the southern part of the Chubu region, Tokai, characteristics of agriculture for cultivation of vegetables and tea on mainly Red-Yellow soil under mild climate are described, including efforts toward effective use of fertilizers.

The Kinki, Chugoku, and Shikoku regions are located in the west-central part of Japan. The major soil great groups distributed in these regions are Brown Forest soils (47.6%), Red-Yellow soils (16.0%), and Fluvic soils (14.2%) with very limited distribution of Andosols (8.6%), reflecting mountainous geography. Those used for agricultural land are dominated by Fluvic soils (65.5%) followed by Brown Forest soils (14.2%) and Red-Yellow soils (7.8%), reflecting high ratio of paddy (72.8%) in agricultural fields. In these regions, diverse types of agriculture are conducted corresponding to a variety of soil types with various geographical and climatic circumstances, including paddy rice production as well as the production of vegetables (e.g., traditional vegetables), fruits (e.g., orange in Wakayama and Ehime Prefectures and Japanese apricot (Ume) in Wakayama Prefecture), and tea in upland fields. Among them “Minabe-Tanabe Ume system” and “Nishiawa slope farming system” are designated as globally important agricultural heritage systems (GIAHS) in these regions. Environmentally friendly agriculture has been carried out, which is defined as sustainable agriculture in which crop productivity is well balanced with environmental quality by recycling materials and reducing the input of chemical fertilizer and pesticides. A wide variety of countermeasures has been also accomplished to reduce greenhouse gas emissions and leaching of nitrate, and harmful chemical substances are also discussed.

Kyushu is the most southerly island among Japan’s main islands. The landscape of Kyushu has been formed through volcanic activity where volcanic soils (Andosols) are widely distributed in the central and southern part of the island. Okinawa is the southern half of the Nansei Islands, which extends approximately 1200 km from Kyushu to Taiwan. The soils of Okinawa are far different from the soils of Japan’s mainland. The three main soils are Red-Yellow soils, Calcareous Eutrosols, and Terrestrial Regosols, all having low soil fertility. Kyushu has a warm and rainy climate, while Okinawa has a subtropical oceanic climate. However, typhoons and torrential rains are frequent in both regions during summer and autumn, leading damage to fields and crops behind them. Kyushu is the second largest food producer on a monetary basis next to Kanto including diverse sectors such as paddy rice, arable crops, vegetables, and fruits. Okinawa, on the other hand, produces sugarcane, pineapple, tropical fruits, and so on by taking advantage of its subtropical climate. Moreover, large-scale livestock production is active through both regions. Like other regions of the globe, environmental issues related to modern agriculture are challenges, including nitrate contamination of groundwater, greenhouse gas emission, soil erosion, and so on. Beside dominating modern agriculture, traditional agriculture with thought-provoking soil management practices still survives in these regions.