Approaches to reduce sulfur emissions during combustion by using in situ sorbent additives have proven to be nominally successful in reducing SO2 emissions from coal-fired boilers. Concerning sulfur release from biomass combustion, however, relatively little work has been published. Accordingly, the objective of the current research was to investigate sulfur-binding sorbent additives that can be mixed with annual biomass fuels to obtain an increased retention of sulfur in the bottom ash. To do so, laboratory-scale experiments were performed with five annual biomass fuels and five Ca-based sorbent additives, using various sorbent/fuel contact arrangements and stoichiometries, in the temperature range of 800-1100 degrees C. From the relevant practical findings from the lab-scale experiments, additional demonstrations were made with wheat straw and added limestone using a large-scale fixed bed reactor (FBR). The retention of a given element in the ash was quantified by the difference according to a simple mass balance on the system, with sulfur being the element of primary interest. The effects of sorbent chemistry, raw fuel chemistry, and sorbent/fuel contact arrangement were considered initially, providing a context for the further discussion of S-retention on a larger scale. Consideration was also given to the following elements: Ca, Cl, K, Mg, Na, P, and Si; the complex interactions between S, Ca, K, and Si were found to be particularly relevant. The promotion of sulfur retention in annual biomass ash by a calcium-based sorbent was found to depend substantially on the raw fuel chemistry and on the combustion temperature. As temperatures rise to 800 degrees C, Si in the raw fuel tends to preferentially react with K and Ca, such that a relative abundance of Si makes the cation species unavailable for the sulfation reaction that binds sulfur as a solid product. At temperatures between 800 and 1100 degrees C, sulfation reactions become favorable, but are limited in their effectiveness to the fraction of fuel-S that remains as char-S after the initial devolatilization phase. The FBR experiments suggest that the insights developed at the lab scale are applicable to considerably larger scales as well. In practical terms, it was found that the rule of thumb developed for optimum sorbent addition for in situ coal combustion desulfurization, Ca-sorbent/S-fuel 2, is not sufficient for biomass fuel. Instead, a simple and suitable biomass-specific index for sorbent effectiveness is introduced as an indicator for achieving maximum sulfur retention by the ash.