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

Figures & data

Figure 1. Ternary diagram of soil texture classification by ISSS and FAO/USDA system (n = 267). Every used soil is plotted by each particle size fraction and texture classification

Table 1. Distribution of soil groups of used soils by comprehensive soil classification system of Japan First Approximation (Obara et al. 2011)

Great soil group	Sub-total	Soil group	n
Man-made soils	0	Artifactual soils	0
		Reformed soils	0
Organic soils	34	Peat soils	34
Podzols		Podzols	0
Andosols	31	Regosolic Andosols	0
		Gleyed Andosols	8
		Wet Andosols	16
		Fulvic Andosols	0
		Non-allophanic Andosols	2
		Allophanic Andosols	5
Dark Red soils		Calcaric Dark Red soils	0
		Dystic Dark Red soils	0
		Eutric Dark Red soils	0
Lowland soils	183	Lowland Paddy soils	22
		Gley Lowland soils	83
		Gray Lowland soils	56
		Brown Lowland soils	15
		Regsolic Lowland soils	7
Red–Yellow soils	0	Argic Red–Yellow soils	0
		Cambic Red–Yellow soils	0
Stagnic soils	2	Stagnogley soils	0
		Pseudogley soild	2
Brown Forest soils	0	Brown Forest soils	0
Regosols	0	Volcanogenous Regosols	0
		Sandy Regosols	0
		Lithosols	0
		Terrestrial Regosols	0
Unknown			17

Figure 2. Sampling locations of used soils

Table 2. Comparison of various methods to estimate silt contents by FAO/USDA system from ISSS soil particle size distribution (n = 267)

Method	Symbol	Variables	RMSE %	Likelihood	AIC
Log-linear	(a)	cl, si, fs, cs	7.8	−478	961
	(b)	cl + si, fs, cs	3.6	−390	784
	(c)	cl, si, s	5.1	−428	860
Log-normal	(d)	cl, si, fs, cs	9.3	−498	1001
	(e)	cl, si, s	8.6	−489	982
Multiple regression	(f)	si, fs, cs	3.1	−370	748
	(g)	si, s	3.7	−393	792
Skaggs et al. (2001)	(h)	cl, si, fs	3.3	−379	764
Minasny and McBratney (2001)	(i)	si, s	10.9	−517	1060

cl, clay; si, silt; fs, fine sand; s, sand; cs, coarse sand.

Figure 3. Comparison of various methods to estimate silt contents of FAO/USDA (si_FAO/USDA) from ISSS soil particle size distribution. The alphabet in the parenthesis in the first line of each graph correspond to the symbols in Table 2

Table 3. The standard deviations (sd) and coefficient of variations (cv) of four cross-validations by using multiple regression Equations (8)(8) $s{i}_{USDA/FAO}=1.305s{i}_{ISSS}+0.396f{s}_{ISSS}+0.100c{s}_{ISSS}-12.323$(8) and (9(9) $s{i}_{USDA/FAO}=1.533s{i}_{ISSS}+0.314s_{ISSS}-20.903$(9) )

	Equation (8)(8) $s{i}_{USDA/FAO}=1.305s{i}_{ISSS}+0.396f{s}_{ISSS}+0.100c{s}_{ISSS}-12.323$(8)				Equation (9)(9) $s{i}_{USDA/FAO}=1.533s{i}_{ISSS}+0.314s_{ISSS}-20.903$(9)
	Coefficient	sd	cv		Coefficient	sd	cv
Silt (si)	1.305	0.086	6.6		1.533	0.111	7.2
Fine sand (fs)	0.396	0.044	11.1		−
Coarse sand (cs)	0.100	0.057	56.7		−
Sand (s)	−				0.314	0.043	13.8
Intercept	−12.323	4.514	36.6		−20.903	5.523	26.4

Table 4. Accuracy ratio of classification of soil texture to FAO/USDA system from estimation by multiple regression of Equation (8)(8) $s{i}_{USDA/FAO}=1.305s{i}_{ISSS}+0.396f{s}_{ISSS}+0.100c{s}_{ISSS}-12.323$(8) and Equation (9)(9) $s{i}_{USDA/FAO}=1.533s{i}_{ISSS}+0.314s_{ISSS}-20.903$(9) with ISSS soil particle size distribution

		Accuracy ratio (%)
Soil texture	n	Equation (8)(8) $s{i}_{USDA/FAO}=1.305s{i}_{ISSS}+0.396f{s}_{ISSS}+0.100c{s}_{ISSS}-12.323$(8)	Equation (9)(9) $s{i}_{USDA/FAO}=1.533s{i}_{ISSS}+0.314s_{ISSS}-20.903$(9)
Sand	―	―	―
Loamy sand	1	100	100
Sandy loam	27	100	96
Loam	85	98	95
Silt loam	26	100	88
Silt	―	―	―
Sandy clay loam	2	100	100
Clay loam	65	98	95
Silty clay loam	36	86	81
Sandy clay	―	―	―
Silty clay	13	100	100
Clay	12	100	100
Total	267	97	93

Table 5. The relationship between soil texture classification by FAO/USDA and some corresponded moisture properties in Japanese paddy soils and comparison to the ‘typical values’ given by Allen et al. (1998)

	Field capacity (−3.1 kPa)				Wilting point (−1500 kPa)
	The 1st quartile	The 3rd quartile	n		The 1st quartile	The 3rd quartile	n	Field capacity†	Wilting point†
Sand								7 − 17	2 − 7
Loamy sand	26	26	1		7	8	3	11 − 19	3 − 10
Sandy loam	33	41	43		11	14	52	18 − 28	6 − 16
Loam	33	44	127		13	17	156	20 − 30	7 − 17
Silt loam	36	45	20		13	16	25	22 − 36	9 − 21
Silt								28 − 36	12 − 22
Sandy clay loam	29	43	6		13	15	7
Clay loam	37	47	97		17	20	108
Silty clay loam	38	46	36		18	21	41	30 − 37	17 − 24
Sandy clay
Silty clay	29	46	10		19	22	11	30 − 42	17 − 29
Clay	38	48	10		17	21	14	32 − 40	20 − 24

†: Data from Figure 19 in Allen et al. (1998)

Figure 4. Boxplots for the relationship between soil texture categorized by FAO/USDA classification system and field capacity (−3.1 kPa; n = 350) or wilting point (−1500 kPa; n = 417) in Japanese paddy soils

Obara, H., T. Ohkura, Y. Takata, K. Kohyam, Y. Naejima, and T. Hamazaki. 2011. “Comprehensive Soil Classification System of Japan First Approximation.” Bulletin of National Institute for Agro-Environmental Sciences 29: 1–72. in Japanese.

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