Changes in Soil Organic Carbon and Nitrogen Stocks in Long-Term Experiments in Southern Brazil Simulated with Century 4.5

Abstract

ABSTRACT:The Century model has successfully simulated soil organic matter dynamics in many agroecosystems. However, initial applications in southern Brazil produced mixed results. The objective of this study was to calibrate and validate Century 4.5 to simulate soil carbon (C) and nitrogen (N) dynamics under diverse soil management practices in subtropical Brazil. Soil C and N data from two long-term experiments established on a degraded Acrisol in the early 1980s were used. Treatments were conventional or no-tillage; grass or grass/legume cropping systems; and corn with or without mineral N fertilizer. The calibration process iteratively modified model parameters to match simulated values of C additions and Soil Organic Carbon (SOC) and Soil Organic Nitrogen (SON) stocks to field data measured throughout the 25 years of the experiments. Improved fit between measured and observed data was obtained after key parameter changes. Soil C and N stocks were simulated accurately after these modifications were implemented. Other experimental treatments were used to validate the model. Century successfully simulated increases in C and N stocks under no-tillage cropping systems including legumes. However, the model overestimated Soil Organic Matter (SOM) decomposition in treatments with low N availability, like oat/corn without N fertilizer. Overall, Century version 4.5 showed adequate performance in simulating C and N trajectories of contrasting cropping systems commonly found in southern Brazil. The few discrepancies between measured and modeled SOC stocks do not preclude using Century in regional-scale applications to assess impacts of agricultural practices on soil C and N in southern Brazil.

Organic Carbon and Physical Properties in Sandy Soil after Conversion from Degraded Pasture to Eucalyptus in the Brazilian Cerrado

“…The CER contain the highest C pool (285.04 Mg ha -1 ), followed by the others. Highest values for the 0.00-0.30 m layer were reported by Sisti et al (2004) and Fernandes and Fernandes et al (2013) studying native Cerrado vegetation under anthropogenic influence (66.55 Mg ha -1 ), undegraded long-term pasture (55.85 Mg ha -1 ), and long-term degraded pasture (56.10 Mg ha -1 ).…”

Assessing strategies to enhance soil carbon sequestration with the DSSAT‐CENTURY model

“…The spin‐up simulations and trial runs using DSSAT‐CENTURY default parameters for litter and SOC decomposition overestimated SOC in CT and DT treatments in both experiments (data not shown). Previous studies suggested site‐specific calibrations with modifications of the “cultivation factor” used in the CENTURY model as a unitless multiplier to increase SOC and structural litter decomposition rates for a period of 30 days after tillage or incorporation of organic residues into the soil (Bolinder, VandenBygaart, Gregorich, Angers, & Janzen, 2006; Porter et al, 2010; Weber et al, 2016). Simulations using this approach required increasing the default cultivation factor from 1.6 up to 20.0 (+1,150%) to decrease the overestimation of SOC stocks in the CT treatment from Manhattan.…”

“…Both procedures (spin‐up simulations and trial runs) were repeated for CT MF and NT MF treatments in Manhattan and DT R1 and NT R1 treatments from the Cruz Alta site, with modifications of the SOC decomposition parameters (Porter et al, 2010) until SOC predicted by the DSSAT‐CENTURY model had good agreement with observations in all treatments selected for calibration. The model required modifications of default respiration losses from both metabolic and structural litter decomposition for tilled soils in both locations (Table 1) following a previous study with the Century 4.5 model (Weber, Mielniczuk, & Tornquist, 2016). No modifications of any of the default parameters of the DSSAT‐CENTURY model were required for NT soils.…”

“…The model calibrated with default and modified parameters for NT and tilled soils, respectively, was then validated using the other treatments available in both experiments: CT CO, CT OF, NT CO and NT OF in Manhattan, and DT R0, DT R2, NT R0 and NT R2 in Cruz Alta. Although using treatments from the same experimental sites, the model was validated with an independent dataset with a greater number of observations from treatments that were not used for the calibration procedure (Musinguzi et al, 2014; Weber et al, 2016). The use of treatments with N inputs and crop rotations for the validation phase helped to test the accuracy of the model in simulating SOC under contrasting tillage practices and biomass inputs (Bruun, Christensen, Hansen, Magid, & Jensen, 2003).…”

Simulating Crop Yield, Soil Nitrogen, and Organic Carbon in No-Tillage Crop Sequences in a Subtropical Climate in Brazil

“…Aiming at the feasibility of employing decision support systems in different regions and climates, computational models seem to be a valuable alternative to estimate the amount of carbon and organic nitrogen in the soil, depending on climatic conditions and cultural and soil management practices, in a given period (Weber et al, 2016). The decision support system for agrotechnology transfer (DSSAT) is widely used to simulate crop yield, development, and income.…”