Evaluation of nonexchangeable potassium content of agricultural soils in Japan by the boiling HNO₃ extraction method in comparison with exchangeable potassium

Figures & data

Table 1. Number of samples in relation to soil type and land use.

		Number of samples
Soil type^a	Relevant soil type^b	Paddy	Upland	Total
Peat soils	Hemists	5	3	8
Sand-dune Regosols	Psamments	0	1	1
Volcanogenous Regosols	Vitrands	0	3	3
Wet Andosols	Aquands	3	2	5
Non-allophanic Andosols	Udands	4	3	7
Andosols	Udands	5	36	41
Lowland Paddy soils	Aquepts	47	1	48
Gley Lowland soils	Aquents	25	3	28
Gray Lowland soils	Aquents	3	3	6
Brown Lowland soils	Ochrepts	0	14	14
Gray Upland soils	Aquepts	0	2	2
Terrestrial Regosols	Orthents	0	2	2
Dark Red soils	Udalfs	0	2	2
Red soils	Udults	0	1	1
Yellow soils	Udults	3	6	9
Brown Forest soils	Ochrepts	0	1	1
Total		95	83	178

^aBy Classification of cultivated soils in Japan (3rd approximation) (Cultivated soil classification committee 1995).

^bBy Soil Taxonomy (dominant type is indicated) (Soil Survey Staff 2014).

Figure 1. Locations of the sampling sites. ●: Volcanic soils. ○: Non-volcanic soils.

Table 2. Median, arithmetic mean, maximum, minimum and coefficient of variation of exchangeable K (exK), nonexchangeable K (neK), hot HNO₃ extractable K, and total K content of agricultural soils in Japan.

	exK	neK	hot HNO3-K^a	Total-K
	(mg kg^−1)	(mg kg^−1)	(mg kg^−1)	(g kg^−1)
Median	209	255	493	15.1
Arithmetic mean	262	303	564	15.6
Maximum	1304	1120	1822	32.3
Minimum	43	0	117	4.30
Coefficient of variation (%)	74	71	53	38

^aBy 1 mol L⁻¹ hot HNO₃ extraction method.

Table 3. Correlation coefficients between nonexchangeable K (neK) content and selected physicochemical properties of the soils.

	Sand	Silt	Clay	Fixed NH4^+-N	Total-C	Alo+1/2Feo	Total-K
neK	−0.05	0.22	0.07	0.41	−0.51	−0.53	0.62
Statistical significance	ns	**	ns	**	**	**	**

** and ns indicate statistical significance at the level of p < 0.01 and ‘not significant’, respectively.

Table 4. Arithmetic mean of nonexchangeable K (neK), neK/Total-K ratio, exchangeable K (exK), exK/Total-K ratio, and total K content of agricultural soils in Japan with reference to soil type.

Soil type^a	Number of samples	neK	neK /Total-K	exK	exK /Total-K	Total-K	neK /(neK+exK)	Fixed NH4^+-N	Silt	Clay	Alo+1/2Feo	Total-C
		(mg kg^−1)	(%)	(mg kg^−1)	(%)	(g kg^−1)	(%)	(mg kg^−1)	(g kg^−1)	(g kg^−1)	(g kg^−1)	(g kg^−1)
Peat soils	8	224	1.5	294	2.2	15.6	44.9	157	271	295	7.6	47.7
Sand-dune Regosols	1	288	1.1	43	0.2	25.1	87.0	11	22	19	1.3	6.3
Volcanogenous Regosols	3	141	1.7	411	5.7	8.90	37.4	10	168	111	13.9	27.9
Wet Andosols	5	132	1.1	281	2.6	11.5	37.1	68	245	209	17.7	62.3
Non-allophanic Andosols	7	258	1.8	295	2.1	13.0	46.9	67	260	211	15.4	64.4
Andosols	41	110	1.2	345	3.7	9.56	29.2	44	242	203	35.2	51.4
Lowland Paddy soils	48	387	2.2	184	1.2	17.9	66.1	102	274	209	5.2	22.2
Gley Lowland soils	28	344	1.9	207	1.2	18.2	62.5	142	289	267	5.9	24.1
Gray Lowland soils	6	351	1.8	260	1.3	20.6	56.8	91	237	184	4.3	18.3
Brown Lowland soils	14	525	2.7	367	2.1	19.1	56.9	195	316	199	6.3	18.1
Gray Upland soils	2	238	1.5	150	0.9	15.8	59.4	54	298	310	3.3	15.5
Terrestrial Regosols	2	753	2.9	308	1.2	26.9	71.6	448	430	414	3.9	11.1
Dark Red soils	2	451	2.8	353	2.2	16.0	57.1	240	393	512	4.0	11.4
Red soils	1	172	0.9	52	0.3	19.9	76.8	385	177	658	1.7	1.8
Yellow soils	9	383	2.3	230	1.4	16.5	64.1	141	266	248	2.7	13.8
Brown Forest soils	1	274	2.0	264	2.0	13.5	50.9	99	339	340	3.0	9.0
Total	178	303	1.9	262	2.1	15.6	52.9	109	269	228	13.0	31.8

^aBy Classification of cultivated soils in Japan (3rd approximation) (Cultivated soil classification committee 1995).

Table 5. Arithmetic mean of nonexchangeable K (neK), neK/Total-K ratio, exchangeable K (exK), exK/Total-K ratio, and total K content of agricultural soils in Japan with reference to region.

Region	Number of samples	neK	neK /Total-K	exK	exK /Total-K	Total-K	neK /(neK+exK)	Fixed NH4^+-N	Silt	Clay	Alo+1/2Feo	Total-C
		(mg kg^−1)	(%)	(mg kg^−1)	(%)	(g kg^−1)	(%)	(mg kg^−1)	(g kg^−1)	(g kg^−1)	(g kg^−1)	(g kg^−1)
Hokkaido	60	248	1.6	275	2.2	14.3	47	121	271	222	13.8	34.0
Tohoku	22	257	2.2	300	2.8	12.2	49	87	300	255	12.8	39.4
Kanto	20	173	1.6	354	3.8	10.2	32	62	231	219	31.7	46.2
Hokuriku-Chubu	25	426	2.1	178	0.9	20.4	69	117	276	223	8.0	21.3
Kinki	11	542	2.7	239	1.1	20.6	71	89	250	203	3.9	24.5
Chugoku	12	377	2.0	231	1.3	19.7	62	73	276	205	6.8	31.9
Shikoku	5	405	2.2	177	1.0	18.5	69	143	302	210	2.7	17.1
Kyushu	15	239	1.5	263	1.9	15.6	49	74	219	187	14.5	32.3
Okinawa	8	399	2.2	214	1.2	17.8	67	284	342	399	3.0	8.8
Total	178	303	1.9	262	2.1	15.6	53	109	269	228	13.0	31.8

Figure 2. Relationship between the content of exchangeable K (exK) and nonexchangeable K (neK). Andosols (53 samples): Wet Andosols, Non-allophanic Andosols, and Andosols. Lowland soils (96): Lowland Paddy soils, Gley Lowland soils, Gray Lowland soils, and Brown Lowland soils. Red Yellow soils (10): Red soils and Yellow soils. Dark Red soils (2). Terrestrial Regosols (2). Regosols (4): Sand-dune Regosols and Volcanogenous Regosols. Peat soils (8). Upland soils (3): Gray Upland soils and Brown Forest soils.

Cultivated soil classification committee 1995: Classification of Cultivated Soils in Japan (3rd Approximation), p. 17. Miscellaneous publication of the National Institute of Agro-Environmental Sciences, Tsukuba, Japan.

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Soil Survey Staff 2014: Soil Taxonomy (12th Ed.), United States Department of Agriculture & Natural Resources Conservation Service, Washington, DC, pp. 360.

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