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Conversion of soil particle size distribution and texture classification from ISSS system to FAO/USDA system in Japanese paddy soils

2020; Taylor & Francis; Volume: 66; Issue: 3 Linguagem: Inglês

10.1080/00380768.2020.1763143

1747-0765

Tomoki Takahashi, Keiko Nakano, Rikiya Nira, Etsushi Kumagai, Mizuhiko Nishida, Mari Namikawa,

Soil Geostatistics and Mapping

The conversion between the two different systems, ISSS and FAO/USDA, of particle size distribution and soil texture classification is useful to characterize soil physical properties and usage of each published. The objective of this study is to test some functions that have been published for conversion from ISSS to FAO/USDA system for Japanese paddy soils and to select the best method. We tested the topsoils of 267 Japanese paddy fields using the log-linear method, log-normal method, multiple regression method, Skaggs et al.'s method, and Minasny and McBratney's method. The least AIC was obtained using multiple regression method, and the equation derived was given as follows:siFAO/USDA = 1.305siISSS + 0.396fsISSS−0.100csISSS − 12.323where si, fs, and cs are the percentage of silt, fine sand, and coarse sand respectively; ISSS and FAO/USDA is the fractionation system; and its RMSE was 3.1%. For the case that only the total sand content (s) is available instead of fine sand and coarse sand, the following equation was obtained:siFAO/USDA = 1.533siISSS + 0.314sISSS − 20.903 (RMSE = 3.7%)Among the non-empirical methods, the best estimation method was Skaggs et al.'s method, and its RMSE was 3.3%. The soil texture classification by FAO/USDA system using estimated particle size fractions by the above equation can be classified to correct categories. The accuracy ratio of the classification was 93-97%.