ABSTRACT
Surface residues decompose more slowly than those that are incorporated by tillage because of reduced contact with soil micro-organisms. The chapter hypothesizes that increased surface residue accumulation under reduced vs. conventional tillage causes reduced mass and energy exchange between soil surfaces and the atmosphere that in turn cause changes in soil temperature and water content that favor increased carbon storage. It seeks to test this hypothesis using the mathematical model ecosys in which energy exchange among the atmosphere, plant canopies, and both soil and residue surfaces are explicitly simulated at high temporal resolution. The model algorithms of particular relevance to the hypothesis proposed concern the determination of surface residue mass, the effect of tillage on surface residue mass, and the effects of surface residue mass on gas and energy exchange between the soil and the atmosphere. Simulated tillage and residue incorporation caused an increase in CO2 evolution through an increase in specific microbial respiration.
