Modification of fuel compositions can reduce ash fouling and slagging, corrosion, and environmental impacts for thermochemical conversion systems. Leaching was used as a feedstock pretreatment to improve the properties of selected agricultural, forestry, and energy crop biomass, including rice straw, wheat straw, corn stover, switch-grass, Miscanthus, Jose tall wheatgrass, and Douglas fir wood. Crude and leached solids were characterized for changes in ash fusibility, heating value, major element concentrations, and other properties. Leachates were analyzed for major and trace elements and organic species. Ash contents were in all cases significantly reduced although simultaneous inorganic and organic material extraction led to more complex outcomes in fuel properties due to possible changes in the composition of residual solids. Declines in ash concentrations were therefore not always accompanied by increases in heating value or improvements in initial ash melting temperatures, although melt flow temperatures in all cases increased, in some cases by more than 500 degrees C. The trends in melt behavior are generally predicted from phase equilibria using reduced ash compositions. Sugars (1.5 - 103.5 mg/g dry matter) and organic acids (0.6 - 57.6 mg/g dry matter) constituted the major fractions of the identified organic extracts and may have potential for coproduct recovery. (C) 2014 Elsevier B.V. All rights reserved.