Carbon Stocks and Pools in Relation to the Texture of Kaolinitic Soils from the Brazilian East Coast

Gomes, João Bosco Vasconcellos; Silva, Carlos Alberto; Ferreira, Tamara Letícia de Azevedo; Ferreira, Mozart Martins; Inda, Alberto Vasconcellos; Curi, Nilton

doi:10.1590/18069657rbcs20170260

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Division - Soil Processes and Properties, Commission - Soil Chemistry • Rev. Bras. Ciênc. Solo 42 • 2018 • https://doi.org/10.1590/18069657rbcs20170260 copy

Carbon Stocks and Pools in Relation to the Texture of Kaolinitic Soils from the Brazilian East Coast

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT:

Extremely kaolinitic soils of Tertiary age elevations on the Brazilian east coast present a wide range of texture, which is recognized as one of the main factors controlling the soil organic matter contents. This study aimed to investigate the organic C storage of different compartments of kaolinitic soils. The studied soils had a wide particle size gradient, were under native forest vegetation, and located on Brazil's eastern coast (Coruripe - CF, Umbaúba - UF, Nova Viçosa - VF, Sooretama - SF, and Itaboraí - IF). The forest cover of all sites allows to record soil properties reference values for a land use condition closer to that of the original sites. We determined soil organic C (SOC) content and SOC stock up to a depth of 1 m, C of topsoil (0.00-0.08 m), aggregate size classes, and dissolved organic carbon (DOC) of the soil surface horizon (A horizon). Soil C stocks at the 0.00-1.00 m depth ranged from 105 to 137 Mg ha⁻¹ and were not regulated by soil texture. The SF soils stored more C up to a depth of 1 m, while lower mean C stocks were found for UF and CF soils. Soil texture was not a reliable index to predict the C contents of the aggregate size classes of the 0.00-0.08 m layer (within each class and in total, using equivalent soil mass of the classes). The most clayey soils had a high percentage of 2-4 mm aggregates and, as a consequence, high aggregate stability indices, which are positively correlated to silt plus clay contents of the soil surface horizon. The proportion of DOC in relation to the total organic C of the surface soil horizon was high for IF and UF areas, which are the less preserved forest fragments among all studied fragments.

Keywords:
dissolved organic C; aggregate size distribution; Coastal Tablelands; organic matter-mineral complexes

Area	Code	Soil class		Texture ⁽²⁾ (2) Mean of three profiles.	Slope	Chronology/Lithology	Annual dry season	Conservation of forest fragments ⁽³⁾ (3) Classification based on in loco observations and on the factors described in Machado et al. (2012) , Magnago et al. (2014) , and Uhlmann et al. (2014) .	Drainage	Fe oxides ⁽⁴⁾ (4) Fe oxides in the clay fraction, mean of three samples (one per pedon) of the B diagnostic horizon - extraction performed via sulfuric acid digestion.
Area	Code	SiBCS ⁽¹⁾ (1) PA = Argissolo Amarelo ; LV = Latossolo Vermelho ; LA = Latossolo Amarelo ; dx = Distrocoeso ; ex = Eutrocoeso ; f = fragipânico ; t = típico .	Soil Taxonomy	Texture ⁽²⁾ (2) Mean of three profiles.	Slope	Chronology/Lithology	Annual dry season		Drainage
					%					%
Coruripe	CF	PAdx-f	Ustult	sandy/fine loamy	1-2	Tertiary/Barreiras	summer	moderate to good	moderately well drained	3
Umbaúba	UF	PAdx-f	Ustult	coarse loamy/fine loamy	1	Tertiary/Barreiras	summer	moderate	moderately well drained	5
Nova Viçosa	VF	LVex-t	Udox	clayey (fine/very fine)	1	Tertiary/Barreiras (with influence of Proterozoic materials)	winter (driest month with rainfall >60 mm)	moderate	well drained	8
Sooretama	SF	PAdx-t	Ustult	sandy/fine loamy	1-2	Tertiary/Barreiras	winter	good	well drained	4
Itaboraí	IF	LAdx-t	Ustox	clayey (fine/very fine)	22-25	Tertiary/Macacu	winter	tolerable	well drained	7

Area ⁽¹⁾ (1) All under native forest: CF = Coruripe; UF = Umbaúba; VF = Nova Viçosa; SF = Sooretama; IF = Itaboraí. P was extracted by Mehlich-1 and K+ by HCl extraction (Mehlich, 1953); Ca2+, Mg2+, and Al3+ by KCl extraction (McLean et al., 1958); H+Al by calcium acetate extraction at pH 7 (Shaw, 1959); BD (bulk density) by the mass:volume ratio in volumetric ring soil samples; and particle size distribution by the pipette method (Gee and Bauder, 1986).	P Mehlich	Ca²⁺	Mg²⁺	K⁺	Al³⁺	H+Al	BD	Sand	Silt	Clay
	mg dm⁻³	------------------------------------------------------------cmol_c dm⁻³------------------------------------------------------------					Mg m⁻³	------------------------------dag kg⁻¹------------------------------
CF	2.20	2.27	0.93	0.09	0.23	2.84	1.15	89	2	9
UF	1.23	1.27	0.63	0.09	0.27	3.09	1.32	81	4	15
VF	5.30	8.30	1.50	0.35	0.00	2.33	1.09	51	8	41
SF	1.32	0.60	0.30	0.04	0.70	5.66	1.24	90	1	9
IF	2.37	0.20	0.20	0.04	2.63	10.50	1.32	54	8	38

Soil layer	Clay					Bulk density
Soil layer	SF ⁽¹⁾ (1) All under native forest: CF = Coruripe; UF = Umbaúba; VF = Nova Viçosa; SF = Sooretama; IF = Itaboraí. Means followed by different lowercase letters in a line indicate differences (p<0.05) in clay and bulk density values among different forest areas at each soil layer. Clay distribution determined by the pipette method (Gee and Bauder, 1986) and bulk density by the mass:volume ratio in volumetric ring soil samples.	CF	UF	IF	VF	SF	CF	UF	IF	VF
m	---------------------------------------------------------g kg⁻¹---------------------------------------------------------					---------------------------------------------------------Mg m⁻³---------------------------------------------------------
0.00-0.17	83 a	90 a	150 b	375 c	448 d	1.26 a	1.15 a	1.34 a	1.27 a	1.27 a
0.17-0.42	210 b	119 a	219 b	484 c	613 d	1.36 a	1.39 a	1.55 b	1.38 a	1.41 a
0.42-1.00	281 a	322 ab	386 b	509 c	649 d	1.41 b	1.44 b	1.57 c	1.32 ab	1.28 a

	C stock	Organic C	Clay	Silt + clay
	0.00-0.17 m
Organic C	0.90 ^ * and **** = level of significance of 5 and 1 %, respectively.
Clay	0.13	0.16
Silt + clay	0.11	0.17	0.99 ^ * and **** = level of significance of 5 and 1 %, respectively.
Bulk density	-0.36	-0.63 ^* * and ** = level of significance of 5 and 1 %, respectively.	0.18	0.16
	0.17-0.42 m
Organic C	0.98 ^ * and **** = level of significance of 5 and 1 %, respectively.
Clay	-0.01	-0.02
Silt + clay	0.04	0.03	0.99 ^ * and **** = level of significance of 5 and 1 %, respectively.
Bulk density	-0.19	-0.35	-0.06	-0.05
	0.42-1.00 m
Organic C	0.92 ^ * and **** = level of significance of 5 and 1 %, respectively.
Clay	0.01	0.19
Silt + clay	0.10	0.28	0.98 ^ * and **** = level of significance of 5 and 1 %, respectively.
Bulk density	-0.01	-0.39	-0.51	-0.51

Soil layer	Soil organic C stock
Soil layer	SF ⁽¹⁾ (1) All under native forest: CF = Coruripe; UF = Umbaúba; VF = Nova Viçosa; SF = Sooretama; IF = Itaboraí. Different lowercase letters in a line indicate differences (p<0.05) among different forest areas at each soil layer. The C stock was calculated according to Veldkamp (1994) .	CF	UF	IF	VF
m	-------------------------------------------------------------------------------------------Mg ha⁻¹-------------------------------------------------------------------------------------------
0.00-0.17	48.2 b	40.2 ab	31.9 a	41.0 ab	46.1 b
0.17-0.42	43.5 c	21.1 a	31.5 abc	36.7 bc	26.9 ab
0.42-1.00	45.8 ab	43.6 a	41.2 a	57.6 b	37.4 a
0.00-1.00	138 b	105 a	105 a	135 ab	111 ab

Area ⁽¹⁾ (1) All under native forest: CF = Coruripe; UF = Umbaúba; VF = Nova Viçosa; SF = Sooretama; IF = Itaboraí.	Silt + clay ⁽²⁾ (2) Mean value (n = 3). MA = macroaggregates; MWD = mean weight-diameter of aggregates; MGD = mean geometric-diameter of aggregates. Mean values followed by different letters in the same column are significantly different by Duncan's test, p<0.05. Silt+Clay distribution was determined by the pipette method (Gee and Bauder, 1986); aggregate size classes by was determined dry sieving, adapted from Haynes (2000) ; and MWD and MGD were determined by Kemper and Rosenau (1986) .	Aggregate size class						MA	MWD	MGD
		2-4 mm	1-2 mm	0.5-1 mm	0.25-0.50 mm	0.105-0.25 mm	0.053-0.105mm	MA	MWD	MGD
	g kg⁻¹	-------------------------------------------------------------------------------------------------------%-------------------------------------------------------------------------------------------------------							-----------mm-----------
CF	90	20 a	26 a	14 b	18 d	15 e	7 b	78 a	1.07 a	0.87 a
SF	100	25 b	36 b	15 b	15 c	7 c	3 a	91 c	1.30 b	1.03 b
UF	190	32 b	28 ab	12 b	13 c	10 d	6 b	84 b	1.39 b	0.99 b
IF	460	62 d	31 ab	2 a	3 a	1 a	1 a	98 d	2.19 d	1.37 d
VF	490	53 c	21 a	13 b	8 b	4 b	1 a	95 d	1.94 c	1.22 c

Area ⁽¹⁾ (1) All under native forest: CF = Coruripe; UF = Umbaúba; VF = Nova Viçosa; SF = Sooretama; IF = Itaboraí, n = 3. Values followed by different capital letters in the same row and lowercase letters in the same column are significantly different by Duncan's test (p<0.05). Organic C content of aggregate size classes was measured using an Elemental Analyzer (Vario TOC Cube model).	Aggregate size class						Sum of classes
	4-2 mm	2-1 mm	1.0-0.5 mm	0.5-0.25 mm	0.25-0.105mm	0.105-0.053 mm	Sum of classes
	Organic C content of soil aggregate size classes						TOC_ag
	--------------------------------------------------------------------------------------g kg⁻¹--------------------------------------------------------------------------------------
CF	52.3 Da	49.5 CDa	47.7 CDa	43.3 BCa	32.7 Aa	40.0 Bb	44.9 a
SF	51.9 Aa	39.6 Aa	44.8 Aa	40.4 Aa	42.3 Aa	13.3 Aa	42.5 a
UF	24.2 Da	22.0 CDa	20.9 BCa	18.7 ABa	15.9 Aa	17.8 Aa	21.0 a
IF	41.6 Ba	41.3 Ba	38.6 Ba	40.9 Ba	40.4 Ba	30.9 Aab	41.2 a
VF	47.1 Aa	45.6 Aa	45.8 Aa	44.9 Aa	38.6 Aa	47.0 Ab	45.7 a
C distribution by soil aggregate size classes (%C)
	--------------------------------------------------------------------------------------------%--------------------------------------------------------------------------------------------
CF	23.3 CDa	28.1 Da	14.9 ABCb	16.9 BCd	10.5 ABc	6.3 Ab	100
SF	31.4 Cab	30.8 Ca	15.5 Bb	14.7 Bcd	6.8 ABb	0.8 Aa	100
UF	35.8 Db	29.1 Ca	11.5 Bb	11.5 Bbc	7.2 ABb	4.9 Ab	100
IF	61.9 Cc	31.4 Ba	1.8 Aa	2.7 Aa	1.5 Aa	0.7 Aa	100
VF	54.5 Fc	20.9 Ea	12.4 Db	7.7 Cab	3.5 Ba	1.0 Aa	100

Properties	Correlation coefficient (r)
Properties	Axis 1	Axis 2
Silt + clay content of A horizon ⁽¹⁾ (1) The silt + clay content of the A horizon was not included in the NMS analysis.	-0.37	-0.78 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.
Organic C content of 2-4 mm aggregate size class	-0.89 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.	0.20
Organic C content of 1-2 mm aggregate size class	-0.89 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.	0.07
Organic C content of 0.5-1 mm aggregate size class	-0.91 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.	0.16
Organic C content of 0.25-0.5 mm aggregate size class	-0.97 ^* , , and **** = significant at 5, 1, and 0.1 % probability, respectively.	0.03
Organic C content of 0.105-0.25 mm aggregate size class	-0.94 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.	-0.09
Organic C content of 0.053-0.105 mm aggregate size class	-0.69 ^* *, , and ***** = significant at 5, 1, and 0.1 % probability, respectively.	-0.01
Sum of organic carbon of soil aggregates	-0.94 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.	0.05
C distribution – 2-4 mm aggregate size class	-0.28	-0.88 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.
C distribution – 1-2 mm aggregate size class	0.04	-0.20
C distribution – 0.5-1 mm aggregate size class	0.07	0.82 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.
C distribution – 0.25-0.5 mm aggregate size class	0.26	0.92 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.
C distribution – 0.105-0.25 mm aggregate size class	0.31	0.94 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.
C distribution – 0.053-0.105 mm aggregate size class	0.41	0.74 ^ , , and **** = significant at 5, 1, and 0.1 % probability, respectively.

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[1] *Corresponding author: E-mail: joao.bv.gomes@embrapa.br