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Title: Modeling organic carbon dynamics under no-tillage and plowed systems in tropical soils of Brazil using CQESTR

Author
item LEITE, L - EMBRAPA
item Doraiswamy, Paul
item CAUSARANO, H - VISITING SCIENTIST
item Gollany, Hero
item MENDONCA, E - UNIV FEDERAL DE VICOSA

Submitted to: Soil and Tillage Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/24/2008
Publication Date: 9/23/2008
Citation: Leite, L.F., Doraiswamy, P.C., Causarano, H.J., Gollany, H.T., Mendonca, E.S. 2008. Modeling organic carbon dynamics under no-tillage and plowed systems in tropical soils of Brazil using CQESTR. Journal of Soil and Tillage Research. 102: 118-125.

Interpretive Summary: The management practices that affect soil carbon stocks were studied for the tropical region of Brazil. The objective of the study was to simulate the carbon dynamics as affected by tillage practices in two tropical soils (Ultisol and Oxisol) in southeastern and northeastern Brazil. The CQUESTR model was used to simulate the changes in carbon stocks and field data was used to calibrate the model for no-tillage (NT), conventional tillage (CT) and reduced tillage practices (RT). In 2006, in the southeast, TOC stocks in the 0-20 cm were 28.8, 23.7, and 22.0 Mg ha-1 under NT, RT and CT, respectively and in the northeast, were 36.0, 33.8 and 32.5 Mg ha-1 under NT, RT and CT, respectively. The CQESTR model underestimated total organic carbon (TOC) in both experiments, especially under no-tillage systems. One primary reason for this is because the model does not make adjustments for inclusion of clay mineralogy which is necessary for simulation of TOC in the tropics. In spite of this, measured and simulated values of TOC were well correlated in the 0-20 cm layer and showed acceptable performance in the prediction of TOC in tropical soils of Brazil.

Technical Abstract: CQESTR simulates the effect of several management practices on soil organic carbon stocks. The model had been calibrated and validated in temperate regions. Our objective was to calibrate the CQESTR model and evaluate its performance for simulating carbon dynamics as affected by tillage practices in two tropical soils (Ultisol and Oxisol) in southeastern and northeastern Brazil. In the southeast (20.75 S 42.81 W) tillage systems consisted of no-tillage (NT), reduced tillage (RT) (one disc plough and one harrow leveling (RT1), or one heavy disc harrow and one harrow leveling (RT2)) and conventional tillage (CT) (two heavy disc harrow followed by one disc plough and two harrow leveling). In the northeast (7.55 S 45.23 W), tillage systems consisted of NT, RT (one chisel plow and one harrow leveling) and CT (one disk plow, two heavy disk-harrowing and two harrow leveling). With respect to initial conditions (native forest) CQESTR estimated a decrease in total organic carbon (TOC) stocks in plowed and no-tillage systems. In 2006, in the southeast, TOC stocks were 28.8, 23.7, 23.2 and 22.0 Mg ha-1 under NT, RT2, RT1 and CT, respectively and in the northeast, were 36.0, 33.8 and 32.5 Mg ha-1 under NT, RT and CT, respectively. The model estimated carbon emissions varying from 1.28 (NT) to 3.67 Mg ha-1 year-1 (CT) in the southeast and from 1.13 (NT) to 3.04 (CT) Mg ha-1 year-1 in the northeast. CQESTR underestimated TOC stocks in both sites, especially under no-tillage systems, indicating that adjustments (e.g. the inclusion of clay mineralogy) are necessary for more accurate simulation of TOC in the tropics. In spite of this, measured and simulated values of TOC in the 0-20 cm layer were well correlated (northeast, R2=0.88, p<0.05; southeast, R2 =0.94, p<0.01) showing acceptable performance in the prediction of TOC in two tropical soils of Brazil.