Simulation of regional ecosystem dynamics of carbon and nitrogen in croplands in a changing global climate: Application to Ohio croplands

The biogeochemical cycles of carbon (C) and nitrogen (N) connect all the abiotic and biotic components of ecosystems to one another, and thus, are closely coupled with variations in productivity and nutrient cycling. The local and regional disturbances such as heavy reliance on fossil fuels, deforestation, and degradative management practices, have important implications for long-term ecosystem productivity regionally as well as climate change globally. C and N budgets are, therefore, significant ecosystem-level indicators that assist in evaluating long-term productivity of ecosystems, and in designing sustainable management practices and policies in a changing global climate. Assessment of impacts of economic, energy and population growth on CO ₂ emissions by a multiple linear regression model, revealed the importance of such socio-economic driving forces as population and consumption growth, and energy intensity, in stabilizing GHG emissions. Two generic simulation models for croplands were devised to quantify long-term temporal changes in regional C sources and sinks in response to global climate change and management practices.; A comparison of observed and simulated SOC values gave an R2 of 0.85 for the Waite Permanent Rotation Trial (Australia) and of 0.80 for the 470 northwest Ohio sites. The simulations for Ohio continuous corn, soybean, wheat and oats croplands revealed that quantity (growth of C₄ vs. C₃ species) and quality (C:N ratio and lignin content) of crop residue inputs to the soil are the major mechanisms that control steady state SOC storage. The magnitude and rate of mitigating atmospheric C-N emissions by croplands depends on the difference between the initial and steady state SOC contents. The interactive effect of CO₂-fertilization and increased soil temperature had a positive influence on long-term SOC-N storage since corn growth, a C₄ species, stimulated by the increased temperature and increased C:N ratio of residues caused by CO₂-fertilization offset mineralization rates of SOC-N accelerated by the increased temperature. However, accelerated mineralization of SOC-N by the increased temperature led to a slight decrease in steady state SOC pool in continuous soybean, wheat and oats (C₃ species) croplands. Sensitivity analysis of the models showed that steady state SOC-N storage increased with decreasing temperatures, increasing clay content, low harvest index, and conservation management practices (through higher residue inputs and suppressed decomposition and mineralization rates of SOC-N pools).