Assessing the carbon stock of cultivated pastures in Rondônia, southwestern Brazilian Amazon

SANQUETTA, CARLOS R.; BASTOS, ALEXIS DE S.; SANQUETTA, MATEUS N.I.; BARBERENA, IARA M.; CORTE, ANA P. DALLA; QUEIROZ, ALEXANDRE; ALMEIDA, LUIZ FELIPE P.U.

doi:10.1590/0001-3765202220210262

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CROP SCIENCE • An. Acad. Bras. Ciênc. 94 (4) • 2022 • https://doi.org/10.1590/0001-3765202220210262 copy

Assessing the carbon stock of cultivated pastures in Rondônia, southwestern Brazilian Amazon

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Cattle ranching is the primary land-use of deforested areas in the Brazilian Amazon. Deforestation precedes pasture establishment, implying tremendous amounts of greenhouse gas emissions caused by carbon stock losses. Despite several studies addressing carbon storage in forests, there is a lack of data regarding cultivated pastures. Hence, the estimation of greenhouse gas emissions associated with land-use change becomes uncertain. In this study, we assessed the carbon stock of cultivated pastures located in Rondônia, southwestern Brazilian Amazon. A total of 50 squared plots of 1 m² were randomly allocated in cattle ranching farms covered by Oxisols (Dystrophic Yellow and Dystrophic Red-Yellow Latosols). Carbon fraction ranged from 0.36 for belowground biomass to 0.45 gC.g^-1 d.m. for aboveground biomass. The average total carbon stock was 5.17 MgC.ha^-1, with non-significant differences when stratifying data by soil types. Considering data from the III Brazilian Inventory of Anthropogenic Emissions and Removals of Greenhouse Gases, our results suggested that land-use change from primary forests to cultivated pastures resulted in a loss of 192.54 MgC.ha^-1, which corresponds to a net emission of 705.98 MgCO₂eq.ha^-1 to the atmosphere. This study provides valuable information to improve the Brazilian Inventory of Anthropogenic Emissions and Removals of Greenhouse Gases.

Key words
climate change; deforestation; land-use change; signal grass

Term	Unit	Definition	Formula
Aboveground biomass (AGB)*	Mg.ha^-1	Dry matter of all living tissues - pseudostems, true stems, nodes and leaves
Belowground biomass (BGB)*		Dry matter of living coarse roots (diameter ≥ 2mm)
Necromass (N)*		Dry matter of non-living materials both above and belowground (e.g., dried leaves, stems, and roots)
Carbon fraction (CF)	gC.g^-1 d.m.	Grams of C for each gram of dry matter	$C F = \frac{m_{c}}{d . m .}$
Carbon stock (CS)	MgC.ha^-1	Mega gram of C per hectare	$C S = B . C F$
CO₂ equivalent	MgCO₂eq.ha^-1	Molecular weight ratio of CO₂ and C	$C O_{2} e q = C S . \frac{44}{12}$
Root-shoot ratio (R)		Ratio between belowground and aboveground biomass	$R = \frac{B G B}{A G B}$
Dead-live ratio (DL)		Ratio between necromass and living biomass (aboveground + belowground)	$D L = \frac{N}{A B G + B G B}$

Dry matter (Mg.ha^-1)	LAd				LVAd				Total
Dry matter (Mg.ha^-1)	AGB	BGB	N	Total	AGB	BGB	N	Total	AGB	BGB	N	Total
Mean	2.37	5.90	4.89	13.15	3.94	3.77	4.40	12.10	3.15	4.83	4.64	12.63
SD	3.09	5.07	3.76	10.88	2.02	2.90	3.24	7.43	2.70	4.22	3.48	9.24
Minimum	0.27	0.69	0.91	2.36	1.03	0.63	0.81	2.74	0.27	0.63	0.81	2.36
Maximum	11.05	18.25	18.21	47.51	10.05	12.13	12.16	33.39	11.05	18.25	18.21	47.51
CV%	130%	86%	77%	83%	51%	77%	74%	61%	86%	87%	75%	73%
Partitioning%	18%	45%	37%		33%	31%	36%		25%	38%	37%
R	2.49				0.96				1.53
DL	0.59				0.57				0.58
n	25				25				50

Carbon stock (MgC.ha^-1)	LAd				LVAd				Total
Carbon stock (MgC.ha^-1)	AGB	BGB	N	Total	AGB	BGB	N	Total	AGB	BGB	N	Total
Mean	1.06a	2.13a	2.11a	5.31 ^ns	1.76a	1.35a	1.93a	5.03 ^ns	1.41a	1.73a	2.03a	5.17
SD	1.38	1.86	1.65	4.48	0.90	1.02	1.41	3.08	1.21	1.52	1.54	3.81
Minimum	0.12	0.25	0.41	1.04	0.46	0.27	0.36	1.20	0.12	0.25	0.36	1.04
Maximum	4.94	6.65	7.98	19.57	4.50	4.42	5.33	13.90	4.94	6.65	7.98	19.57
CV%	130%	87%	78%	84%	51%	76%	73%	61%	86%	88%	76%	74%
Partitioning%	20%	40%	40%		35%	27%	38%		27%	33%	39%
n	25				25				50

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[1] Correspondence to: Mateus Niroh Inoue Sanquetta E-mail: mateus.sanquetta@gmail.com