In evaluating future agroecosystem sustainability, a main concern is the effect of climate change (e.g., increased atmospheric CO2, elevated air temperature, increased/decreased water availability) on agronomic production. Many of the crop production models discussed previously have been used to investigate potential impacts of climate change on yield. Agricultural modeling is a practical approach to studying this global phenomenon as it is difficult to wholly quantify the interactions between climate change effects and crop production based on limited plot-scale experiments or controlled-environment studies. Another major international issue with respect to global climate change is to improve our understanding of how agroe-cosystem soils and management contribute to climate change through emission of greenhouse gases such as CO2, CH4, N2O, NO, and NH3. Land-use changes are believed to account for about 8% and other agriculture sources about 15% of the anthropogenic greenhouse emissions. Several agricultural models (e.g., Century and DNDC) are being utilized to devise and evaluate management practices that will minimize greenhouse gas emissions and increase C sequestration, such as no-tillage and residue management, adding legumes into rotations, and optimal timing of manure applications. Changes in climate modify the soil environment, especially soil water and temperature and also a number of concurrent processes dependent on these including evapotranspiration, runoff, and erosion. Current global climate change models have predicted an increase in frequency of extreme events such as droughts and heavy rainfalls, but it is not known how these changes will affect agricultural production in different ecosystems around the world. Furthermore, it is unclear how extreme climate events will change worldwide soil resources - for example, changes in soil properties from accelerated soil erosion by wind and water. Agricultural models are increasingly needed to evaluate the magnitude of these influences in different agroecosystems and locations around the world, and to devise strategies for mitigating potential adverse effects. For example, agricultural models are just now being used to develop special management practices during drought conditions. Drought-mitigation strategies may include shift in production among regions and changes in crops, cultivars, and management practices, such as crop rotations and water conservation measures.
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