Simulation of soil organic matter dynamics and nutrient cycling in agroecosystems

Management interacts with natural driving variables in an agroecosystem to have a major impact on the processes which control the ecosystem properties. The scCENTURY soil organic matter (SOM) model integrates the effects of climate and soil driving variables with agricultural management to simulate C, N, P, S, and water dynamics in the soil-plant system, with an emphasis on long-term SOM dynamics. A new agroecosystem version of the scCENTURY model was designed for the simulation of complex agricultural management systems including crop rotations, a variety of tillage practices, fertilizer, and irrigation.; The results of two wheat-fallow tillage comparison experiments in Nebraska were used for calibration of the crop production sub-model and validation of the soil C and N dynamics. The scCENTURY model closely predicted the decline in SOM following the conversion of native grassland to wheat-fallow management, in each of the 3 tillage treatments, but the accumulation of mineral N during the fallow period was underestimated.; The simulation analysis of alternative crop management systems for the semi-arid Great Plains, with reduced periods of summer fallow and more intensive crop rotations incorporating corn, sorghum, and millet clearly showed benefits in increased crop production and SOM, in comparison to the traditional wheat-fallow system. Simulation of the effects of climate change and elevated CO{dollar}sb2{dollar} demonstrated the importance of the direct effects of CO{dollar}sb2{dollar} on crop growth. Wheat production is predicted to increase with elevated CO{dollar}sb2,{dollar} while production of corn, sorghum, and millet declined due to lower summer rainfall in the climate change scenario. SOM was predicted to be increased by climate change and/or elevated CO{dollar}sb2{dollar} in all the systems in which wheat was grown.; The scCENTURY model was successfully parameterized to predict the dynamics of C, N, P, and S pools in grazed, fertilized, grass-clover pasture in New Zealand. However, in the unfertilized treatment the model greatly underestimated the amount of soil organic matter, even though pasture yields were overestimated.; In all systems the future trends in SOM are dependant on interactions between the current SOM levels, soil properties, climate, and agricultural management.