Generating generic response signals for scenario calculation of management effects on carbon sequestration in agriculture: approximation of main effects using CENTURY

In this study, a well bounded and validated biogeochemical model, CENTURY, is used to mimic behaviour of soil carbon under different agricultural management regimes in Australian conditions to provide simple soil carbon response signals for use in a multi-criteria, spatial framework for analysis of management effects on carbon storage. The study is concerned with relative change in soil carbon resulting from change in management, and not concerned with absolute values either of change or final stock. Simulations were run for a range of starting soil carbon levels, soil physical properties, and climate sites using two carbon pool allocations within the model. A simplified set of agricultural land management options was used consisting of warm season native grassland, warm/cool season mixed native grassland, improved pasture, continuous wheat, conservation tillage, and long and short cereal rotations with lucerne. There were large differences in simulation results between crop and pasture systems and management types within systems. Within management types, starting soil carbon levels had the major influence on simulation outcomes. The derived carbon response signals for agricultural management practices, summarised over soils and climate, tended to underestimate losses under cropping and overestimate gains from perennial grassland when compared to field data. The value of these signals in a scenario analysis is discussed.