Origin of the soil texture classification system used in Japan

Abstract

The classification systems for soil particle size ranges and soil texture differ among countries and/or associations. Unique systems have also endured in Japan over the last six decades. However, the original reports explaining the rationale for these systems have gradually been lost, so there is no source written in either Japanese or English for authors to reference the origin of the Japanese soil classification systems. In this light, we reviewed the origin of the Japanese classification systems for soil particle size ranges and soil texture. The size range system was adopted from International Society of Soil Science (ISSS) standards. The soil texture classification system was introduced by Tommerup in his paper at the ISSS Commission I (Soil Physics) meeting in 1934. This soil texture classification system was modified by Yamanaka in 1955, and was henceforth adopted as the conventional soil texture classification system in Japan. This ISSS-defined soil texture classification system has been in use since that time.

Key words:

• soil texture class
• size range of particle
• Japanese system
• International Society of Soil Science system
• historical context

INTRODUCTION

The need to designate soil textural classes first arose when soil researchers engaged in field work. The class to which a soil belonged was judged by its “feel” when some of the surface material was rubbed between the fingers. Those who did early survey work closely observed the textural designations used by farmers. They soon learned that there were sometimes surprising inconsistencies in terms, whereby a soil composition term used in one location meant something completely different elsewhere. Soil researchers in the field would examine a soil sample from a soil textural class, give it a name and then send the soil to the laboratory for analysis of its particle size range and soil textural classification (Davis and Bennett 1927; Kyuma 2009). Today, soil textural class is determined by the weight ratio of the soil particle size (Soil Survey Division Staff 1993; Nakai 1997; Food and Agriculture Organization of the United Nations 2006). When determining a soil texture classification, there is no significance given to its physical properties or the soil’s crop productivity; therefore, some researchers simply describe the weight ratio of soil particle size class (Mu et al. 2008; Nakao et al. 2012; Fujii et al. 2013). The classification systems for particle size ranges and soil texture used by countries and/or associations outside Japan also differ. In Japan, soil textural classifications are determined by the particle size distribution (Fig. 1a) and the proportion of the particle size distribution (Fig. 2), known and described as the ISSS (International Society of Soil Science, restructured into the International Union of Soil Sciences or IUSS in 1998) method. Soil texture cannot fully describe soil properties, but even today, thus-conditioned soil texture is still deemed to be suitable in order to gain an overview of a soil’s physical-chemical properties and fundamental fertility. Therefore, soil texture is mentioned in almost every basic Japanese soil science textbook (Inoue 1997; Inubushi 2001; Matsunaka 2003; Sakurai 2005; Hayashi 2010). Soil texture is also used as a basis for determining suborder in Japan’s soil classification system (Obara et al. 2011).

Figure 1 Soil Particle Range Systems (a) ISSS: Schucht (1914), ISSS (1929) (b) Explanatory texts of Agronomic maps of the Empire of Japan, “Dosei-zu setsumeisho”: Tsuneto (1888) (c) Agricultural Sciences of Japan: Agricultural Sciences of Japan (1926) (d) FAO: FAO (1990) and FAO (2006); FAO (1968) and FAO (1977) used USDA-defined soil particle ranges. (e) USDA (from 1938): USDA (1938), Soil Survey Staff (1951) (f) USDA (until 1938): USDA (1896) (1) Before 1947; fine gravel (2) When determining soil texture, fine gravel was included in the soil fraction. VC: very coarse.

Figure 2 International Soil Science Society (ISSS)-defined soil texture classification system used in Japan (Yamanaka 1955).

The ISSS soil texture classification system contains 12 textural classes that are defined by their ratios of sand, silt and clay (Fig. 2). The determination of soil texture classifications by particle size distribution originated from the soil textural designations used by farmers. Thus, while there must be some underlying rationale for dividing soil texture into 12 classes, no basic Japanese soil science textbooks published in the last few decades offer any such rationale. Nor does Japan’s soil texture classification method handbook credit any source (Nakai 1997). Consequently, scientific papers published today, including our previous ones, which mention soil texture classes and soil particles size ranges based on the ISSS standard do not cite the correct source of their methods (Kitagawa et al. 2005; Maejima et al. 2011; Eguchi and Tamura 2012; Makabe-Sasaki et al. 2013; Matsumoto et al. 2013). Thus, addressing this scientific oversight and clarifying the source is important for both Japanese researchers and the international scientific community of soil researchers. In this paper, we review the origin of the Japanese systems for classifying soil texture and soil particle size ranges.

HISTORY OF SOIL TEXTURE CLASSIFICATION IN THE EARLY DAYS OF JAPAN’S MODERN SOIL SCIENCE

The Japanese word for soil texture is “dosei.” Kyuma (2009) clearly explains the history of soil texture in Japan in the early days of modern soil science, and suggests that in those days, “dosei” originally had three meanings:

1. Nature (mainly physical properties) of crop productivity; “dosei” for productivity;

2. Elements, physical properties and classification basis of soil; a concept used in soil surveys, i.e., “dosei chosa” for soil map, “dosei-zu” established by Max Fesca and “dosei” for soil survey;

3. Soil class derived from the ratios of clay, silt and sand; “dosei” for soil textural class determined by particle size distribution.

Today, “dosei,” when it means soil texture, is used for “particle size distribution.” But the meaning of “dosei” as “productivity” and as “soil survey” also influenced “dosei” meaning “soil texture,” especially for Japan’s government soil scientists up until the early 1970s. Before examining the explanation for why the ISSS soil textural classification system has been used in Japan, we first review the history of the definition of “dosei” as soil textural class. Soil survey, “dosei chosa,” in Japan was first established by the Geological Survey of Japan and then was made into a more sophisticated survey by Max Fesca, which altogether had a great impact on defining soil texture (Tomoda 1978; Kyuma 2009). In this case, “dosei” means soil but not soil texture. Fesca was a German agricultural scientist employed by the Japanese government as a foreign advisor from 1882 to 1894 (Kyuma 2009). He compiled the first soil map, “Agronomic map of Kai Province with explanatory text,” in 1887 (Fesca 1887), and the terms “soil” and “map” in the title were translated to “dosei” and “zu” in Japanese, respectively. Thus, in this case, “dosei” means the soil itself and not soil texture. In the explanatory text, Fesca defined 10 soil textures as “dosei” classes, so in this case, “dosei” meant soil texture. Thus, the definition of the term “dosei” was complicated from the time since it was first used. Furthermore, as we describe later in this paper, the soil survey “dosei for soil textural class” came to include all of the aforementioned three meanings. Before Fesca’s work, soil textures in a soil survey were determined not only by the soil particle size distribution but included the organic matter and lime content (Geological Survey of Japan 1882) as well. Then Fesca (1887) defined 10 classes of soil texture: clay, loamy clay, gravel clay, clay loam, loam, sandy loam, gravel loam, sand, loamy gravel and gravel. He decided that the soil texture, “dosei,” would be determined by the distribution of the size range of the soil particles, fine earth (< 4 mm) and coarse clay (< 0.01 mm). He did not present any tabular data corresponding to these 10 soil texture classes or particle size distributions at that time. One year later, however, an “Agronomic map of Musashi Province (Northern Part) with explanatory text” was compiled by Tsuneto (1888) under Fesca’s tutelage. In this description, the soil texture classes (left column of Table 1) were determined by the particle size distribution defined in Fig. 1b. This procedure for determining soil textural classes, as defined by Tsuneto (1888), was also used in the paper “Agronomic map of Awa Province with explanatory text” (Kamoshita 1894). However, in the “Agronomic map of Wakasa and Echizen Provinces with explanatory text” published in 1895 (Hayakawa 1895), the procedure had been changed, as shown in Fig. 1b and Table 2. Hayakawa (1895) determined soil texture from particle size distribution as well as from the soil’s crop productivity, chemical composition and physical-chemical properties. His paper may have been influenced by discourse on soil texture, Dosei ben, (Sato 1914, first edition published in 1874) which was not truly a scientific book, but was widely read throughout Japan at that time (Kyuma 2009). In Dosei ben, soil texture classification was based not only on the size range of soil particles and their stickiness and plasticity used in the field study of the present day (Japanese Society of Pedology 1997), but on crop productivity as well. Minari (1898) determined soil texture on the basis of particle size distribution (Fig. 1b and left column of Table 1) in “Agronomic map of Owari and Mikawa Provinces with explanatory text.” But he also recommended that determinations of soil texture should also involve careful examination of the varieties of the parent rock, the degree of weathering, the soil profile and the soil structure, followed by experiments to determine particle size distribution, chemical composition, physical-chemical properties and nutrient adsorption. Kamoshita (1902) determined soil texture solely from particle size distribution, and he defined the soil texture much more clearly (right column of Table 1) in “Agronomic map of Uzen Province and Akumi District of Ugo Province with explanatory text.” Matsuoka (1905) also determined soil texture solely from particle size in “Agronomic map of Empire of Japan, Bungo Province and south-eastern part of Buzen Province with explanatory text,” but he used the former criteria listed in the left column of Table 1. These historical legacy soil maps are available on the National Institute for Agro-Environmental Sciences (NIAES) Website, the Soil Information Web Browser (http://agrimesh.dc.affrc.go.jp/soil_db/, NIAES 2008). The abovementioned descriptions clarify that during these early years, the system for soil textural classification was not fixed. Japan was undergoing a transitional period in the standardization of soil texture classification, and soil maps of Japan’s provinces continued to be produced by the Ministry of Agriculture and Commerce until 1948 (Hamazaki and Nakai 2002).

Table 1 Examples of soil texture classes described in explanatory texts to the Agronomic maps of the Empire of Japan, “Dosei-zu setsumeisho”

Soil texture class	Definition of the class in the agronomic maps of the empire of Japan
	1888–1905	1902–
Clay (Shoku-do)	Soil containing more coarse clay than very fine earth	Soil containing about 60% of coarse clay
Loamy clay (Joshitsu-shoku-do)	Clay having loam character	Clayey soil between clay and loam
Clay loam (Shokushitsu-jo-do)	Loam having clay character	Soil between clay and loam but not loamy clay
Loam (Jo-do)	Soil containing large amounts of very fine earth but small amounts of coarse clay	Soil containing from 30 to 50% of sand and between clay and sand
Sand (Sa-do)	Soil containing a lot of sand but a little very fine earth	Soil containing about 80% sand
Any gravelly class (Rekishitsu-bo-do)	Soil containing less than half gravel and sand	_______________________________
Any class gravel (Boshitsu-reki-do)	Soil containing more than half gravel and sand	_______________________________
Sandy gravel (Sareki-do)		Soil containing one third very fine soil and two thirds gravel or sand

Table 2 Soil texture classes in explanatory text to the agronomic map of Wakasa and Echizen Provinces, “Wakasa-Echizen dosei-zu setumei-sho” (Hayakawa 1895)

Soil texture class	Character
Clay	Clay is more sticky when wet, and cracks when dry. Its texture is very dense, and air or water does not penetrate easily. It is usually cool, wet and of low crop productivity. It absorbs nutrients and contains a large amount of macronutrients for plant growth.
Loam	Loam contains less coarse clay than clay and is classified between clay and sand. Its crop productivity depends on its chemical contents. It is the best agricultural soil from the point of view of the particle size distribution and physical properties (bulk density, particle density and water constant).
Sand	Sand is usually dry, warm, coarse, light and porous. Therefore, the penetration of water and air is good. Extractable chemicals easily run out, and those contents in it are low.
Gravel	Gravel contains a large number of fragmented rocks. Most plants usually cannot grow on it, but the growth rate of crops in gravel containing some fine soil or more fine soil is a little higher.

There also existed a definition or understanding of soil texture other than that used in soil surveys by the Japanese government during this period. Terashi (1881) translated into Japanese the “Cyclopædia of Agriculture” that had been edited by John Chalmers Morton, a Scotsman. In the text, soil textural class is defined by the ratios of silicate, silicate sand, river cobbles, clay, lime, plant residues and animal residues. The Ministry of Education of Japan (1884) also translated “Elements of Agricultural Chemistry and Geology,” written by the Scotsman James Finlay Weir Johnston, into Japanese. In this text, soil textural class is defined by the ratios of clay and sand. In both of these texts, soil textural classification did not use the Japanese term “dosei.” However, the soil textural classification system based on soil particle distribution had been introduced to Japan before Fesca compiled the first soil map of Japan in 1887, as indicated by the Ministry of Education of Japan publication (1884).

Additionally, each prefecture used its own unique soil textural classifications and soil particle size ranges, which differed from those established by the Japanese government in its soil surveys (Yamanaka and Abe 1896). However, the use of soil particle size ranges for conducting soil surveys in Japan gradually came to be accepted in each prefecture (Agricultural Experimental Station of Niigata Prefecture, 1915; Agricultural Experimental Station of Hiroshima Prefecture 1926) and by Japan’s academics (Seki 1926). However, the soil textural classification systems used in Japan’s soil surveys was not consistently used by all Japanese academics (Uchiyama and Ogawa 1918; Seki 1926). In other publications, only soil particle distribution has been described, and there was no mention of the soil textural classification (Aso and Muramatsu 1907; Daikuhara 1919).

As is clear from the above, in 1884, soil textural classification based on soil particle distribution was already in practice, and this method for determining the soil textural classification had spread to the academic scientists at Japan’s universities. Fesca’s “dosei chosa” soil survey in Japan also determined soil textural class, “dosei,” only on the basis of soil particle distribution at first. However, since “dosei chosa” does not mean soil textural class but soil survey, the definition of “dosei” as a soil science term, especially in Japan’s soil survey, was complicated and had three meanings, as mentioned above: (1) “dosei” for productivity, (2) “dosei” for soil survey and (3) “dosei” for soil textural classification based on particle size distribution. Furthermore, Japan’s soil survey, the procedure for determining “dosei,” i.e., a soil’s textural class, went from being based on soil particle size distribution only to including its distribution along with the soil’s productivity, profile and physical-chemical properties. After the Pacific War, by 1946, the term soil survey in Japan was changed from “dosei chosa” to “dojo chosa.” “Dojo” means soil in Japanese. But in Hokkaido prefecture, soil surveys were called “dosei chosa” until 1972 (Kyuma 2009), which indicates how deeply ingrained the term “dosei” had come to mean “soil survey” in the minds of Japanese government soil scientists.

SOIL TEXTURAL CLASS AS DEFINED BY THE AGRICULTURAL SCIENCES OF JAPAN

The Agricultural Sciences of Japan set up an investigative committee to address soil classification, nomenclature systems and soil survey chaired by Seki in February 1926. In August of that year, the committee submitted its report which included a definition of soil particle ranges (Table 3) and soil textural classes (Fig. 1c; Agricultural Sciences of Japan 1926). This report had been in use until shortly after the Pacific War. On one hand, undoubtedly, the soil textural classification system defined by the Agricultural Sciences of Japan (1926) followed the soil survey system used by Japan’s Ministry of Agriculture and Commerce. But no reason was given as to why the committee chaired by Seki established the soil texture classifications shown in Table 3. The committee defined clay as having a particle size < 0.01 mm, which agreed with Japan’s soil survey, but the size boundary between gravel and sand was set at 2 mm, which was different from the 4-mm boundary used in the surveys. The committee may have taken into account the German and US systems that had been introduced into Japan (Daikuhara 1919), or it may have followed Atterberg’s system which had been proposed to the International Agro-Geologists Conference, “Internationalen Agrogeologenkonferenz” (Atterberg 1912), the precursor of the ISSS, and had been approved at its Commission for Mechanical and Physical Soil Analysis, “Kommission für die mechanische und physikalische Bodenuntersuchung” chaired by Atterberg himself (Schucht 1914).

Table 3 Soil texture classes of the Agricultural Sciences of Japan (1926)

Soil texture class	Content of clay fraction (%)
Clay (Shoku-do)	More than 50
Clayey Loam (Shoku-jo-do)	From 37.5 to 50
Loam (Jo-do)	From 25 to 37.5
Sandy Loam (Sa-jo-do)	From 12.5 to 25
Sand (Sa-do)	Less than 12.5

INTERNATIONAL SOIL SCIENCE SOCIETY’S SOIL PARTICLE RANGES AND TEXTURE CLASSIFICATION USED IN JAPAN

In this section, we review the history of ISSS’ determination of the soil particle ranges and soil texture classifications used in Japan and the era in which these ISSS standards became widely used. The ISSS standard soil particle range used in Japan (Fig. 1a) originated from the method proposed by Atterberg in 1910 to the Commission for Mechanical and Physical Soil Analysis (die Kommission für die mechanische und physikalische Bodenuntersuchung). The soil particle ranges and an analysis method also proposed by Atterberg were approved by the commission in 1913 (Schucht 1914). Both methods proposed by Atterberg were reviewed in a preliminary meeting before the first commission meetings of the International Congress of Soil Science at Rothamsted in 1926 (ISSS 1927). At the first meeting of ISSS in Washington, DC, in 1927, Atterberg’s particle size distribution method was recommended for use thereafter in international publications (ISSS 1929). Atterberg offered a rationale for his proposed soil particle ranges (Schucht 1914, p. 3) as follows:

In a 2.0–0.2 mm particle range, the capillaries [are] too coarse to retain water. This particle group yields dry ground, which is only suitable for use as forest soil. In a 0.2–0.02 mm particle range, the capillaries retain water well. This group constitutes the main component of “good sandy soil” and capillary water moves quickly. In a 0.02–0.002 mm particle range, the capillaries have a compact storage of grains that are too small for the root hairs of grasses to penetrate, and capillary water moves well. This group constitutes the main component of loamy clay soil. In a less than 0.002 mm particle range, capillaries are too small to allow bacteria to move freely and capillary water movement is very slow. This group often constitutes the main component of heavier clay soils.

However, the ISSS-defined soil texture classification system used in Japan was proposed by Tommerup (1934) at ISSS’ Commission of Soil Physics held in Versailles. It is uncertain when the ISSS-defined soil particle ranges and texture classification system began to be used widely in Japan. To the best of our knowledge, the first descriptions of them occur in Kanno’s (1953) handbook, Soil Survey Method. In this handbook, Kanno indicates that the clay, identified as falling within a certain soil particle range defined by the Agricultural Sciences of Japan (1926), includes particles that do not have the characteristics of clay. As a result, some researchers began to use the ISSS-defined soil particle ranges. Kanno recommended a revision of the soil texture classification system defined by the Agricultural Sciences of Japan, and proposed that until these revisions had been submitted, in order to correctly distinguish soil characteristics, researchers should use the ISSS-defined soil texture classification system (Fig. 2; with no distinction between loamy sand and sand, both of which fell into the loamy sand class; Tommerup 1934) or the soil texture classification system of the United States Department of Agriculture (USDA; Fig. 3; Davis and Bennett 1927; Shaw 1928). Yamanaka (1955) pointed out that these soil particle range differences between the Agricultural Sciences of Japan (1926) and ISSS classification systems (Schucht 1914), and the differences in the soil texture classifications between the Agricultural Sciences of Japan (1926) and ISSS (Tommerup 1934), caused transitional confusion. But Yamanaka concluded that the soil particle ranges and soil texture classification system defined by the Agricultural Sciences of Japan (1926) were considered to be a convenient ISSS standard, and suggested further that those classifications defined by the Agricultural Sciences of Japan were essentially no different from those of ISSS. Yamanaka (1955) also divided the loamy sand defined by Tommerup (1934) into loamy sand and sand (Fig. 2) in order to more precisely classify the soil texture of sand dune soil which is widely distributed in Japan. Saito (1978) mentioned that the soil texture classification system used in Japan had introduced by Tommerup (1934) and that this system had later been revised. But Saito (1978) did not mention that the revision had been made by Yamanaka (1955). The soil texture classification system, as revised by Yamanaka (1955), has been generally used as the ISSS standard in Japan since that time.

Figure 3 United States Department of Agriculture (USDA)-defined soil texture classifications used until 1951 (Davis and Bennett 1927). The soil texture classifications of Fig. 4 had been considered prior to 1951 (Joffe 1949).

Figure 4 United States Department of Agriculture (USDA)-defined soil texture classifications used from 1955 (Soil Survey Staff 1951). These soil texture classfications had been considered prior to 1951 (Joffe 1949).

The ISSS-defined soil texture classification system proposed by Tommerup (1934) was constructed by applying the ISSS-defined soil particle ranges proposed by Atterberg (Schucht 1914) to the USDA-defined soil texture classification system (Fig. 3). Thus, the concept of the ISSS-defined soil texture classification system used widely in Japan is based on USDA-defined soil texture classification system concepts (Table 4; Shaw 1928). Until the early 20th century, there had been no nationally standardized soil particle ranges or soil texture classification systems in the United States. Therefore, the USDA constructed soil texture classifications (Fig. 3) based on its soil particle ranges (Fig. 1e; Davis and Bennett 1927). As shown in Table 4, the USDA soil texture classification system was based on the feel of the soil particles when rubbed between the fingers in the field. Soil texture classifications determined by soil particle range (Fig. 3) originated from soil texture classification determined by the feel of the soil (Table 4). Therefore, the ISSS-defined soil texture classification system (Fig. 2) is also derived from the classification method developed in the field (Table 4).

Table 4 United States Department of Agriculture (USDA)-defined soil texture classes and field classification method, corresponding to the International Soil Science Society (ISSS)-defined soil texture classes used in Japan

USDA (Shaw 1928)	Corresponding to ISSS (Tommerup 1934)	Character
Clay: including Sandy Clay and Silty Clay	Heavy Clay, Sandy Clay, Light Clay and Silty Clay	Clay is a fine textured soil that usually forms very hard lumps or clods when dry, and is quite plastic and usually sticky when wet. When the moist soil is pinched out between the thumb and fingers it forms a long, flexible “ribbon.” Some fine clays which are very high in colloids are friable and lack plasticity in all conditions of moisture.
Clay Loam: including Sandy Clay Loam and Silty Clay Loam	Clay Loam, Sandy Clay Loam and Silty Clay Loam	Clay loam is a fine-textured soil which usually breaks into clods or lumps that are hard when dry. When the moist soil is pinched between the thumb and finger it forms a thin “ribbon” which will break readily, barely sustaining its own weight. The moist soil is plastic and will form a cast that will bear much handling. When kneaded in the hand, it does not crumble readily but tends to work into a heavy compact mass.
Silt Loam	Silty Loam	Silt loam is a soil with a moderate amount of the fine grades of sand and only a small amount of clay, over half of the particles being of the size called “silt.” When dry it may appear quite cloddy but the lumps can be readily broken, and when pulverized it feels soft and floury. When wet, the soil readily runs together. Either dry or moist, it forms casts that can be freely handled without breaking, but when moistened and squeezed between thumb and finger, it will not “ribbon” but will give a broken appearance.
Loam	Loam	Loam is a soil having a relatively even mixture of different grades of sand and of silt and clay. It is mellow with a somewhat gritty feel, yet fairly smooth and slightly plastic. Squeezed when dry, it forms a cast that will bear careful handling, whereas the cast formed by squeezing the moist soil can be handled quite freely without breaking.
Sandy Loam	Sandy Loam	Sandy loam is a soil containing high quantities of sand but has enough silt and clay to make it somewhat coherent. The individual sand grains can readily be seen and felt. Squeezed when dry, it will form a cast which will readily fall apart, but if squeezed when moist a cast can be formed that will bear careful handling without breaking.
Sand	Loamy Sand (Yamanaka (1955) divided this class to Loamy Sand and Sand)	Sand is loose and single-grained. The individual grains can readily be seen or felt. Squeezed in the hand when dry it will fall apart when the pressure is released. Squeezed when moist, it will form a cast, but will crumble when touched.

IS THE ISSS-DEFINED SOIL TEXTURE CLASSIFICATION SYSTEM USED IN JAPAN AN INTERNATIONAL METHOD?

We have reviewed the history of the ISSS-defined soil particle ranges and soil texture classification system used in Japan. There are original standards for soil particle ranges and soil texture classifications in every country around the world. ISSS standards for both the soil particle ranges and soil texture classification are employed in Japan. However, while ISSS soil particle ranges are accepted internationally, the ISSS-defined soil texture classification system is not. Verheye and Ameryckx (1984) referred to the ISSS-defined soil texture classification system modified by Yamanaka (1955), but they did not indicate its source and they questioned whether or not it was truly international. The Food and Agriculture Organization of the United Nations (FAO) uses the USDA-defined soil particle ranges (Fig. 1f; Soil Survey Staff 1951) and soil texture classification system (Fig. 4; Soil Survey Staff 1951; FAO 1968). But in 1990, FAO established its own unique soil particle ranges (Fig. 1d; FAO 1990). In general, USDA-defined soil particle ranges and soil texture classifications have been used more widely internationally than the ISSS standards.

CONCLUSION

At present, soil texture classification in Japan is determined by soil particle size distribution. Soil texture classification originated in the field according to the feel of the soil particles when rubbed between the fingers. This field method was subsequently improved to the present determination method. While the ISSS-defined soil particle ranges used in Japan have been recognized internationally, the ISSS-defined soil texture classification system used in Japan has not. The ISSS-defined soil texture classification system used in Japan was originally proposed by Tommerup (1934) to apply the ISSS-defined soil particle ranges to the USDA-defined soil texture classification system. Yamanaka (1955) revised this ISSS-defined soil texture classification system, and this revised system has been used widely in Japan. We have found no Japanese or English references that mention the origin of ISSS-defined soil particle ranges and soil texture classifications used in Japan. Therefore, most researchers have not correctly understood these Japanese standards. We hope this review will promote a more accurate understanding of the soil particle ranges and the soil texture classification system used in Japan.

ACKNOWLEDGMENTS

The authors give special thanks to Kazutake Kyuma, Emeritus Professor of Kyoto University, for his guidance and detailed commentary on our review.