Temporary storage of soil organic matter and acid neutralizing capacity during the process of pedogenetic acidification of forest soils in Kinki District, Japan

Figures & data

Table 1 Brief description of the soils studied

Site	Classification		Altitude (m)	STR	Information on the depth (cm) of the genetic horizons and their soil color^§
	Jpn^†	USDA^‡
MD1	hB	Typic Dystrudepts	110	Thermic	O, 2–0 (7.5YR3/3); A, 0–8 (7.5YR4/6); BA, 8–23 (10YR5/8); Bw, 23–40 (10YR5/8); BC, 40–50+
MD2	hB	Typic Dystrudepts	180	Thermic	A, 0–8 (10YR4/4); BA, 8–20 (10YR6/8); Bw1, 20–45 (10YR7/8); Bw2, 45–62 (10YR6/6); BC, 62–90+ (10YR7/6)
FD	hB	Typic Dystrudepts	230	Thermic	A(o), 0–3 (5YR2/2); BA, 3–14 (10YR4/6); Bw, 14–40 (10YR5/8); BC, 40–55+ (10YR5/8)
OF	hB	Typic Dystrudepts	560	Thermic/mesic	O, 2–0 (7.5YR2/1); A, 0–8 (10YR5/6); Bw, 8–29 (10YR5/8); BC, 29–50 (10YR6/8); R, 50+
ST1	hB	Lithic Dystrudepts	660	Thermic/mesic	A(o), 0–5 (5YR2/1); AB, 5–12 (10YR5/8); Bw, 12–35 (7.5YR5/8); BC, 35–45 (7.5YR5/7); R, 45+
ST2	hB	Lithic Dystrudepts	650	Thermic/mesic	A(o), 0–3 (7.5Y2/2); AB, 3–12 (10YR4/4); Bw1, 12–20 (10YR5/8); Bw2, 20–35 (10YR6/8); R, 35+
MT	nK	Alic Hapludands	800	Thermic/mesic	A(o), 0–2 (10YR1.7/1); AB, 2–15 (10YR4/6); Bw1, 15–35 (10YR5/8); Bw2, 35–55 (10YR6/8); BC, 55–75+ (10YR5/6)
KD1	hB	Lithic Dystrudepts	840	Thermic/mesic	A, 0–3 (7.5YR2/2); BA, 3–12 (10YR5/6); Bw, 12–32 (10YR8/5); BC, 32–44 (10YR6/6); R, 44+
KD2	hB	Humic Dystrudepts	830	Thermic/mesic	A(o), 0–4 (10YR2/3); AB, 4–16 (10YR3/3); Bw1, 16–29 (10YR6/6); Bw2, 29–45 (10YR6/8); BC, 45–60+ (10YR6/8)
TT	hB	Andic Dystrudepts	1210	Mesic	A(o), 0–5 (7.5YR2/3); BA, 5–20 (10YR5/8); Bw, 20–60 (10YR6/8); BC, 60–70 (10YR6/6); R, 70+
OT	nK	Alic Hapludands	1220	Mesic	A(o), 0–8 (7.5YR2/1); BA, 8–24 (7.5YR4/6); Bw, 24–52 (7.5YR5/8); BC, 52–62 (10YR5/8); C, 62–70+ (10YR5/8)
OM	hB	Andic Dystrudepts	1600	Mesic	A(o), 0–5 (7.5YR2/3); A, 5–15 (7.5YR3/3); BA, 15–33 (7.5YR4/4); Bw, 33–45 (10YR4/6); BC, 45–70+ (10YR5/7)
^†According to the Unified Soil Classification System of Japan (Fourth Committee for Soil Classification and Nomenclature 2002). hB, Haplic Brown Forest Soils; nK, non-allophanic Kuroboku soils.
^‡According to Soil Taxonomy (Soil Survey Staff 2006).
^§A(o) horizon described here contains > 200 g C kg^−1 soil and is regarded as a deposited organic layer in the Unified Soil Classification System of Japan.

Table 2 General physicochemical properties of the selected soils

Site	Horizon	Depth (cm)	pH (H2O)	pH (KCl)	pH (NaF)	Exch. bases (cmolc kg^−1)	Exch. Al (cmolc kg^−1)	CEC (cmolc kg^−1)	Total C (g kg^−1)	Sand particles (%)	Silt size (%)	Clay distribution (%)
MD1	O	2–0	3.93	3.16	7.03	3.4	14.6	77.8	312.7	5.5	12.5	82.1
	A	0–8	4.52	3.91	9.61	0.7	9.5	25.4	67.7	11.4	23.8	64.8
	BA	8–23	4.62	3.95	9.64	0.3	7.2	23.7	21.8	10.5	23.4	66.1
	Bw	23–40	4.62	3.92	9.52	0.3	8.3	19.0	13.4	13.3	24.0	62.8
	BC	40–50+	4.69	3.97	9.18	0.2	7.6	16.0	7.4	39.8	17.9	42.3
MD2	A	0–8	4.69	4.09	10.30	1.0	7.5	34.5	121.3	8.8	27.4	63.8
	BA	8–20	4.61	3.90	9.50	0.5	10.9	25.3	36.8	8.2	26.6	65.2
	Bw1	20–45	4.70	3.89	9.44	0.3	9.2	22.5	15.2	7.5	23.5	69.1
	Bw2	45–62	4.71	3.89	9.38	0.3	10.9	22.2	8.7	9.3	27.8	62.9
	BC	62–90+	4.78	3.89	9.35	0.3	11.1	32.9	6.5	10.6	25.1	64.2
KD1	A	0–3	4.59	3.39	7.91	2.4	16.6	34.9	124.4	56.1	18.0	25.9
	BA	3–12	4.73	3.66	9.34	0.6	22.5	34.6	44.6	25.0	27.4	47.5
	Bw	12–32	4.82	3.74	9.39	0.4	17.6	31.6	37.0	20.0	23.8	56.1
	BC	32–44	4.92	3.96	9.32	0.3	9.6	17.9	25.8	46.8	18.7	34.5
KD2	A(o)	0–4	4.00	3.18	7.28	1.4	17.4	55.9	208.3	22.9	25.8	51.2
	AB	4–16	4.21	3.41	8.34	0.5	18.5	38.9	94.5	24.4	28.4	47.2
	Bw1	16–29	4.61	3.73	9.57	0.2	9.3	23.6	26.6	29.2	28.4	42.4
	Bw2	29–45	4.65	3.81	9.50	0.2	7.4	22.5	13.0	33.3	25.4	41.3
	BC	45–60+	4.70	3.88	9.53	0.2	6.1	12.7	9.6	45.5	21.7	32.8
TT	A(o)	0–5	3.58	3.09	7.01	2.4	17.7	54.2	265.0	23.7	27.3	49.0
	BA	5–20	4.08	3.48	8.85	0.6	18.0	29.1	52.2	28.0	24.3	47.6
	Bw1	20–40	4.55	3.86	9.39	0.3	7.6	18.5	26.5	25.5	26.1	48.4
	Bw2	40–60	4.71	4.04	9.68	0.2	4.7	12.9	19.3	22.0	25.6	52.4
	BC	60–70	4.73	4.01	9.36	0.2	5.4	10.9	8.1	35.0	21.7	43.3
OT	A(o)	0–8	3.82	3.17	7.28	1.7	15.7	29.7	223.7	9.7	17.2	73.0
	BA	8–24	4.12	3.56	9.12	0.6	23.9	40.4	76.9	14.2	25.9	59.9
	Bw1	24–38	4.49	3.89	9.98	0.3	10.6	26.9	61.3	20.3	31.8	47.9
	Bw2	38–52	4.65	4.05	10.59	0.2	6.8	21.9	55.9	22.9	37.2	39.9
	BC	52–62	4.75	4.18	11.12	0.1	4.6	17.6	32.4	34.1	19.4	46.5
	C	62–70+	4.80	4.28	10.93	0.1	2.8	12.7	16.3	43.2	16.0	40.8
Site	Horizon	Depth (cm)	Cp (g kg^−1)	Alp (g kg^−1)	Fep (g kg^−1)	Alo (g kg^−1)	Feo (g kg^−1)	Sio (g kg^−1)	Alo+1/2Feo (g kg^−1)	Dominant clay mineral species identified by XRD^†
MD1	O	2–0	43.4	5.6	6.3	6.3	4.8	0.1	8.7	2:1–2:1:1 int > Kao, Gb, Qz > Ch
	A	0–8	17.4	7.4	13.4	7.8	8.3	0.1	11.9	2:1–2:1:1 int > Kao, Gb, Qz > Ch
	BA	8–23	6.3	4.6	8.5	5.2	6.5	0.1	8.4	2:1–2:1:1 int > Kao, Gb, Qz > Ch
	Bw	23–40	4.2	2.9	3.7	4.1	4.2	0.1	6.2	2:1–2:1:1 int > Kao, Gb, Qz > Ch
	BC	40–50+	2.1	1.8	1.3	3.1	3.3	0.1	4.8	2:1–2:1:1 int > Kao, Gb, Qz > Ch
MD2	A	0–8	33.6	10.6	9.7	11.3	6.9	0.1	14.8	2:1–2:1:1 int > Kao, Gb, Qz
	BA	8–20	10.7	6.6	12.5	6.7	9.4	0.0	11.4	2:1–2:1:1 int > Kao, Gb, Qz
	Bw1	20–45	2.2	4.3	7.4	5.1	6.9	0.0	8.5	2:1–2:1:1 int > Kao, Gb, Qz
	Bw2	45–62	3.3	3.8	6.3	4.5	5.2	0.0	7.1	2:1–2:1:1 int > Kao, Gb, Qz
	BC	62–90+	2.3	2.7	2.3	3.9	4.0	0.0	5.8	2:1–2:1:1 int > Kao, Gb, Qz
KD1	A	0–3	28.2	3.5	3.8	5.7	7.0	0.1	9.2	Vt > Mica, Kao, Gb, Qz
	BA	3–12	17.0	5.2	5.0	9.2	11.6	0.0	15.0	Vt > Mica, Kao, Gb, Qz
	Bw	12–32	15.6	5.0	7.2	9.4	16.9	0.0	17.9	2:1–2:1:1 int > Kao, Gb, Qz
	BC	32–44	6.0	3.6	3.6	6.3	8.7	0.1	10.7	2:1–2:1:1 int > Kao, Gb, Qz
KD2	A(o)	0–4	42.1	6.8	6.9	7.2	8.9	0.0	11.7	Vt, 2:1–2:1:1 int > Kao, Gb, Qz
	AB	4–16	29.2	7.2	6.0	8.4	12.1	0.0	14.4	Vt, 2:1–2:1:1 int > Kao, Gb, Qz
	Bw1	16–29	11.5	5.2	4.3	7.9	20.2	0.0	18.0	2:1–2:1:1 int > Kao, Gb, Qz
	Bw2	29–45	6.3	4.0	3.3	5.6	8.8	0.0	10.0	2:1–2:1:1 int > Kao, Gb, Qz
	BC	45–60+	3.8	3.4	3.4	4.0	5.8	0.0	6.9	2:1–2:1:1 int > Kao, Gb, Qz
TT	A(o)	0–5	42.6	4.0	4.3	4.8	5.5	0.0	7.6	2:1–2:1:1 int > Vt, Kao, Gb, Qz
	BA	5–20	19.9	4.6	8.5	6.6	12.7	0.0	13.0	2:1–2:1:1 int > Vt, Kao, Gb, Qz
	Bw1	20–40	11.3	3.6	7.4	5.8	12.6	0.0	12.1	2:1–2:1:1 int > Kao, Gb, Qz
	Bw2	40–60	7.5	3.3	4.3	6.0	10.2	0.1	11.1	2:1–2:1:1 int > Kao, Gb, Qz
	BC	60–70	3.2	1.8	1.6	3.9	5.5	0.1	6.6	2:1–2:1:1 int > Kao, Gb, Qz
OT	A(o)	0–8	43.9	3.6	5.0	4.6	6.4	0.3	7.8	2:1–2:1:1 int > Vt, Kao, Gb, Qz
	BA	8–24	32.3	7.9	16.2	9.4	21.1	0.0	20.0	2:1–2:1:1 int > Vt, Kao, Gb, Qz
	Bw1	24–38	25.2	7.5	13.5	9.0	19.6	0.0	18.8	2:1–2:1:1 int > Kao, Gb, Qz
	Bw2	38–52	20.3	6.9	10.4	10.8	20.8	0.1	21.2	2:1–2:1:1 int > Kao, Gb, Qz
	BC	52–62	16.0	7.4	8.7	11.3	16.4	0.2	19.5	2:1–2:1:1 int > Kao, Gb, Qz
	C	62–70+	8.2	5.1	2.5	9.6	7.9	0.6	13.5	2:1–2:1:1 int > Kao, Mica, Gb, Qz
^†Kao, kaolin minerals; Mica, clay mica; Vt, vermiculite; Ch, chlorite; 2:1–2:1:1 int, 2:1–2:1:1 intergrade minerals; Gb, gibbsite; Qz, quartz.CEC, cation exchange capacity; Alo, Feo, Sio, extraction in the dark with acid (pH 3) 0.2 mol L^−1 ammonium oxalate; Alp, Fep, Cp, organic C; extraction with 0.1 mol L^−1 pyrophosphate at pH 10; XRD, X-ray diffraction.

Figure 1  Acid and alkali titration curves of the soils.

Table 3 Correlation coefficients among the physicochemical properties and titration data of the soils (n = 43)

	pH (H2O)	pH (KCl)	pH (NaF)	Ex.bases	Ex.Al	ECEC	CEC	Clay	TC
Initial pH	0.55	0.93**	0.88**	–0.70**	–0.90**	–0.90**	–0.70**	–0.20	–0.31
Titratable alkalinity by pH 3.0	0.01	0.47	0.73**	–0.21	–0.36	–0.36	–0.05	0.04	0.41
Titratable acidity by pH 8.3	–0.62**	–0.64**	–0.36	0.66**	0.78**	0.79**	0.82**	0.16	0.80**
OH^− consumption in the range of pH 4.5 to 5.5	–0.56	–0.84**	–0.68**	0.66**	0.96**	0.96**	0.86**	0.28	0.41
OH^− consumption in the range of pH 5.5 to 8.3	–0.53	–0.37	–0.07	0.52	0.49	0.49	0.64**	0.06	0.90**
	Cp	Alo	Feo	Ald	Fed	Alp	Fep	Alo + 1/2Feo	Alp + 1/2Fep
Initial pH	–0.18	0.42	0.24	0.50	–0.09	0.13	–0.11	0.34	0.00
Titratable alkalinity by pH 3.0	0.51	0.83**	0.74**	0.82**	0.38	0.79**	0.49	0.82**	0.66**
Titratable acidity by pH 8.3	0.75**	0.35	0.47	0.13	0.36	0.58*	0.58*	0.43	0.61*
OH^− consumption in the range of pH 4.5 to 5.5	0.32	–0.12	0.02	–0.25	0.25	0.10	0.24	–0.05	0.18
OH^− consumption in the range of pH 5.5 to 8.3	0.90**	0.61*	0.71**	0.39	0.42	0.80**	0.71**	0.69**	0.80**
*P < 0.05;
**P < 0.05. CEC, cation exchange capacity; ECEC, effective CEC; TC, total C; Alo, Feo, extraction in the dark with acid (pH 3) 0.2 mol L^−1 ammonium oxalate; Alp, Fep, Cp, organic C; extraction with 0.1 mol L^−1 pyrophosphate at pH 10; Ald, Fed, extraction with a citrate-bicarbonate mixed solution buffered at pH 7.3 with the addition of sodium dithionite at 80°C.

Figure 2  Relationships between (a) titratable alkalinity and Alo (extraction in the dark with acid [pH 3] 0.2 mol L−1 ammonium oxalate), (b) OH− consumption and exchangeable Al and (c) OH− consumption and pyrophosphate extractable C (Cp).

Table 4 Soil solution composition

Site	Depth (cm)	No. of samples	pH	DOC (mmol L^−1)	Na	K	Mg	Ca	Cl	NO3	SO4	Fe	Si	Al			Sum of cations	Sum of anions	Anion deficit
														Total	Inorganic monomeric	Organic monomeric
					(×10^−3 mmolc L^−1)							(×10^−3 mmol L^−1)					(×10^−3 mmolc L^−1)
MD1	15	13	5.16	1.13	135.1	21.9	36.4	21.3	110.0	0.0	65.5	0.2	116.5	17.9	4.6	10.3	277.3	175.6	101.8
	40	12	5.21	0.58**	116.8*	12.4**	25.5**	10.6*	108.6	0.0	41.8**	0.2	96.5*	12.8	6.3	5.9*	211.6***	150.5*	61.2*
MD2	15	16	5.52	0.27	57.4	21.8	22.1	11.1	60.8	0.0	37.6	0.0	43.3	4.0	1.9	1.9	127.6	98.3	29.3
	40	11	5.49	0.18*	66.6	24.5	14.3***	10.1	66.3	0.0	33.4	0.0	48.6	3.0	2.4	1.2*	128.2	99.8	28.4
KD1	15	12	5.08	0.26	105.6	12.5	26.0	13.6	135.6	0.0	41.8	0.0	74.5	10.7	8.5	1.6	200.4	177.4	23.0
	45	11	5.03	0.10***	105.4	6.2*	39.3**	12.8	146.7	0.0	43.1	0.0	53.8*	10.9	8.5	0.9*	206.3	189.8	16.5
KD2	15	12	5.02	0.36	60.0	9.8	20.2	19.0	75.5	3.0	29.1	0.1	60.2	12.1	5.6	5.3	155.6	107.7	47.9
	45	12	5.19**	0.10***	71.8**	6.8*	14.4**	12.3***	68.8	4.3	31.8	0.0**	34.5***	4.4***	3.3**	1.0***	125.4***	104.9	20.6***
TT	15	11	4.74	0.34	43.1	32.6	42.9	54.0	64.3	124.4	31.8	0.2	37.5	22.9	16.1	4.8	262.2	220.6	41.6
	40	12	4.88*	0.19*	47.8	21.8	33.5	64.3	44.3	144.2	16.5**	0.0***	33.0	15.4*	11.9	2.0***	227.6	205.0	22.7*
OT	15	10	4.94	0.31	32.6	6.4	16.5	17.8	54.8	12.0	26.6	0.2	85.2	13.2	7.0	4.2	126.5	93.4	33.1
	45	11	5.23***	0.09***	35.0	2.7*	12.1*	10.0***	39.6*	0.4*	19.3	0.2	31.1***	3.7***	2.5**	1.1***	77.5***	59.3**	18.2***
The concentration of each component in the soil solution from the surface and B horizons is different at *20%,
**5% and
***1% levels, respectively.

Figure 3  Relationships observed among the soil solution compositions. (a) Anion deficit and dissolved organic carbon (DOC), (b) inorganic monomeric Al (Alinorg) and pH and (c) organic monomeric Al (Alorg) and DOC.

Figure 4  Chemical properties and titration data of the soil profiles superimposed with the soil solution composition. Error bars are standard error. Values with the same letter are not significantly different (P < 0.05). Alo, Feo, extraction in the dark with acid (pH 3) 0.2 mol L−1 ammonium oxalate; Alp, Fep, extraction with 0.1 mol L−1 pyrophosphate at pH 10; DOC, dissolved organic carbon.

Figure 5  Chemical properties and titration data of the soil profiles in northern Kyoto superimposed with the soil solution composition. Data are cited from Funakawa et al. (1993a). Error bars are standard error. Values with the same letter are not significantly different (P < 0.05). Alo, Feo, extraction in the dark with acid (pH 3) 0.2 mol L−1 ammonium oxalate; Alp, Fep, extraction with 0.1 mol L−1 pyrophosphate at pH 10; DOC, dissolved organic carbon.

Figure 6  Amounts of (a) titratable acidity, (b) total C and (c) titratable alkalinity on a kmol ha−1 basis. Data presented here include data cited from Funakawa et al. (1993b) and Funakawa et al. (2003). Cp, pyrophosphate extractable C; Exch Al, exchangeable Al.

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