Carbon stocks of an Oxisol after thirty-eight years under different tillage systems

Magalhaes, Sulamirtes S. de A.; Ramos, Fabricio T.; Weber, Oscarlina L. dos S.

doi:10.1590/1807-1929/agriambi.v20n1p85-91

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ENVIRONMENTAL CONTROL AND MANAGEMENT • Rev. bras. eng. agríc. ambient. 20 (1) • Jan 2016 • https://doi.org/10.1590/1807-1929/agriambi.v20n1p85-91 copy

Carbon stocks of an Oxisol after thirty-eight years under different tillage systems

Estoques de carbono em Latossolo após trinta e oito anos sob diferentes sistemas de cultivo

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Soil carbon (C) stock determination can subsidize discussions on the continuity of an agricultural management. This study aimed to evaluate the stocks of total organic C (S_TOC) and labile C (S_LC), and the indices of C lability (CLI), C compartment (CCI) and C management (CMI), and correlate them with chemical and physical attributes of a Red Yellow Latosol (Oxisol) managed for 38 years with different tillage systems in a Cerrado region of Mato Grosso, Brazil. Disturbed and undisturbed soil samples were collected in three layers (0-0.05, 0.05-0.10 and 0.10-0.20 m). The CMI (CLI x CCI) showed higher S_TOC possibly as the tillage depth decreased, because none of the tillage systems conserved S_TOC and S_LC in the layers of 0-0.05 and 0.05-0.10 m, compared with the Native Cerrado, i.e., soil C conservation only occurred in the layer of 0.10-0.20 m. Although the percentage of S_LC in S_TOC was lower, only S_LC was correlated with soil chemical and physical attributes and, based on the multiple linear regression analysis, S_LC was explained in 54% (R²) by the cation exchange capacity and soil micropores. Therefore, for monitoring purposes, the S_LCestimated can be useful to evaluate soil C storage.

Key words:
soil conservation; crop rotation; soil organic matter

Soil use	Symbol	Soil tillage history
Native Cerrado	NC	Fragment of Cerrado (strict sense), without signs of anthropic disturbance, characterized by the presence of small, twisted trees and grasses covering the soil. This area was considered as a control for the comparison with the tillage systems.
Minimum tillage I	MT I	The Cerrado was deforested in 1977, with subsequent cultivation of rice/soybean for 3 years under conventional tillage and, until the 1999/00 season, soybean/corn was cultivated in rotation under conventional tillage, disturbing the soil with heavy harrowing with discs of 32" every 3 years. In 2000/02, cotton was cultivated, followed by gypsum application, two harrowings (32") and seeding of millet in the off-season. In 2002/03, gypsum was applied and the soil was prepared with scarification until 0.30 m, two harrowings (32"), and soybean and corn were sown in the off-season. In 2003/04, gypsum was applied broadcast and cotton was cultivated on corn residues with later destruction of stumps, combining mechanical mowing and a light harrowing to incorporate plant residues. In 2004/07, gypsum was applied, a leveling harrow was used and soybean and millet were cultivated in the off-season. In 2007/08, there were gypsum application, two harrowings (32"), scarification until 0.30 m and cultivation of soybean and corn. In 2008/10, gypsum was applied, a light harrow was used and soybean and corn were cultivated in the off-season. All the fertilizations were performed in the seeding row and followed the technical recommendations for the crops, as also occurred in the systems MT II and MT II, which are described below. Therefore, only in the last two crop seasons there was lower disturbance on soil surface, with a light harrowing before soybean sowing.
Minimum tillage II	MT II	The Cerrado was deforested in 1977, with subsequent cultivation of rice/soybean for 3 years under conventional tillage and, until the 1999/00 season, soybean/corn was cultivated in rotation under conventional tillage, disturbing the soil with heavy harrowing with discs of 32" every 3 years. In 2000/02, millet was cultivated, followed by gypsum application, two harrowings (32") and sowing of cotton. In 2002/03, gypsum was applied and soybean and corn were cultivated in the off-season. In 2003/04, cotton was sown on corn residues. In 2004/06, the soil was prepared with two harrowings (32"), and millet and cotton were sown in rotation. Then, gypsum was applied and the stumps were destroyed, combining a mechanical mowing with a harrowing to incorporate plant residues. In 2006/07, the soil was scarified until 0.30 m and millet and cotton were cultivated in rotation, with later destruction of the stumps. In 2007/08, millet and cotton were sown in rotation, with later destruction of the stumps. In 2008/09, limestone was applied in association with gypsum and soybean and corn were cultivated in the off-season. In 2009/10, cotton was sown on corn residues. Therefore, soil disturbance was more frequent in this tillage system than in the previous one, MT I.
Minimum tillage III	MT III	The Cerrado was deforested in 1976, with subsequent cultivation of rice/soybean for 3 years under conventional tillage and, until the 1999/00 season, soybean/corn was cultivated in rotation under conventional tillage, disturbing the soil with heavy harrowing with discs of 32" every 3 years. In 2000/04, cotton was cultivated, followed by corn, and limestone was applied before the 2001/02 season and incorporated with two harrowings (32"). Cotton stumps were destroyed combining mechanical mowing and harrowing to incorporate plant residues. In 2004/05, the soil was subjected to two harrowings (32"), subsoiled and sown with soybean followed by corn, with later gypsum application. In 2005/06, cotton was cultivated on corn residues. In 2006/10, there were crop rotations with soybean/corn, corn/cotton and soybean/cotton, respectively. Therefore, the soil was harrowed not only when cotton was cultivated, although a heavy harrow was used just at the end of its cycle to destroy the stumps. Thus, soil disturbance was more frequent in this system than in the previous ones (MT I and MT II), and millet was not cultivated.
Intensive pasture	IP	The Cerrado was deforested in 1978 and rice was cultivated from 1978 to 1980. In 1981, Brachiaria brizantha cv. Marandu was planted and weed control was manually performed every 2 years under intensive management with Nelore cattle for fattening, with mean capacity of 7-9 A.U. ha^-1, without animal rotation. Since 1997, every 3 years, the soil has been chemically corrected with the dose of 1,5 Mg ha^-1 of dolomitic limestone, plus a fertilization with 100 kg ha^-1 of single superphosphate as top-dressing. Since 2003, between March and April, 10 tons of cotton hull have been applied. Gypsum was applied broadcast in 2008, in the dose of 500 kg ha^-1.

	S_TOC	S_LC	S_NLC
S_TOC, Mg ha^-1	1
S_LC, Mg ha^-1	0.72^* (1)* P < 0.0001; ⁽¹⁾ (1)*** P < 0.0001;	1
S_NLC, Mg ha^-1	0.98^* (1)* P < 0.0001;	0.55^* (1)* P < 0.0001;	1
pH, H2O	0.13 ^ns ns Not significant	-0.28 ^ns ns Not significant	0.25 ^ns ns Not significant
pH, CaCl₂	0.04 ^ns ns Not significant	-0.46^ P < 0.01: Significant at 0.05 probability level by t-test;	0.17 ^ns ns Not significant
P, mg dm^-3	-0.18 ^ns ns Not significant	-0.47^ P < 0.01: Significant at 0.05 probability level by t-test;	-0.07 ^ns ns Not significant
K, cmol_c dm-³	0.09 ^ns ns Not significant	-0.27 ^ns ns Not significant	0.19 ^ns ns Not significant
Ca, cmol_c dm-³	-0.14 ^ns ns Not significant	-0.57^ P < 0.01: Significant at 0.05 probability level by t-test;	0.01 ^ns ns Not significant
Mg, cmol_c dm-³	-0.03 ^ns ns Not significant	-0.48^ P < 0.01: Significant at 0.05 probability level by t-test;	0.12 ^ns ns Not significant
Al, cmol_c dm-³	0.06 ^ns ns Not significant	0.28 ^ns ns Not significant	-0.02 ^ns ns Not significant
H, cmol_c dm-³	-0.09 ^ns ns Not significant	-0.04 ^ns ns Not significant	-0.09 ^ns ns Not significant
SB, cmol_c dm-³	-0.09 ^ns ns Not significant	-0.55^ P < 0.01: Significant at 0.05 probability level by t-test;	0.06 ^ns ns Not significant
CEC, cmol_c dm-³	-0.15 ^ns ns Not significant	-0.60^* (1)* P < 0.0001;	0.01 ^ns ns Not significant
V (%)	-0.05 ^ns ns Not significant	-0.48^ P < 0.01: Significant at 0.05 probability level by t-test;	0.09 ^ns ns Not significant
Sand, g kg^-1	0.01 ^ns ns Not significant	0.29*	-0.08 ^ns ns Not significant
Silt, g kg^-1	0.03 ^ns ns Not significant	-0.07 ^ns ns Not significant	0.06 ^ns ns Not significant
Clay, g kg^-1	-0.02 ^ns ns Not significant	-0.30^ P < 0.01: Significant at 0.05 probability level by t-test;	0.07 ^ns ns Not significant
Soil de^ns ns Not significant ity, Mg m^-3	0.06 ^ns ns Not significant	0.15 ^ns ns Not significant	0.02 ^ns ns Not significant
Macroporosity, m³ m^-3	0.12 ^ns ns Not significant	0.40^ P < 0.01: Significant at 0.05 probability level by t-test;	0.02 ^ns ns Not significant
Microporosity, m³ m^-3	-0.10 ^ns ns Not significant	-0.47^ P < 0.01: Significant at 0.05 probability level by t-test;	0.03 ^ns ns Not significant
Total porosity, m³ m^-3	0.00 ^ns ns Not significant	-0.24 ^ns ns Not significant	0.07 ^ns ns Not significant

Intercept^* ***** (P < 0.0001): Significant at 0.05 probability level by t-test y0 (1)	Coefficients^* ***** (P < 0.0001): Significant at 0.05 probability level by t-test		N ⁽¹⁾ (1) N - Number of data pairs used in the adjustment;	r ⁽²⁾ (2) r - Pearson coefficient (P < 0.0001);	R²⁽³⁾ (3) R2 - Coefficient of determination;	P F Test	ESE (Mg ha^-1) ⁽⁴⁾ (4) ESE - Estimate standard error;	TRN ⁽⁵⁾ (5) TRN - Test of residual normality through Kolmogorov-Smirnov with correction of Lilliefors (P > 0.05);	Calibration (Mg ha^-1)
	CEC	Mi		r ⁽²⁾ (2) r - Pearson coefficient (P < 0.0001);	R²⁽³⁾ (3) R2 - Coefficient of determination;	P F Test	ESE (Mg ha^-1) ⁽⁴⁾ (4) ESE - Estimate standard error;		Minimum	Maximum
11.252	-0.706	-0.117	45	0.732	0.536	< 0.001	0.962	0.152	0.7041	6.7579

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[1] fabriciotomazramos@gmail.com (Corresponding author)