The role of cover crops has been expanded with the increased use of conservation tillage.  Cover crops can provide environmental benefits such erosion control, building organic matter, and combating soil compaction.  However, prediction of N credits associated with cover crop use, particularly where a blend of widely varying species is used as a cover crop, remains to be resolved.  As N fertilizer costs climb, the incentive increases for an improved ability to predict cover crop effects on N availability for the following crop.  As a first step in answering this question, the objective of this study was to evaluate whether fiber content of cover crop residue could be used to predict N mineralization rate of the tissue.  Five plant materials (wood chips, oat straw, grass hay, alfalfa hay, and kale) representing a range of fiber contents were evaluated for this purpose.  The materials were put in mesh bags and placed in the field to examine the rates of biomass and nutrient loss on the soil surface.  The five materials were also placed in soil in a controlled environment to examine rates of N mineralization across a range of temperatures.  Also discussed here is a greenhouse bioassay where the nutrient content of grass grown with the five plant residues was monitored over time as an indicator of N mineralization rates.  Preliminary analysis from these trials suggest that fiber content has good potential to serve as a predictor of rate of N mineralization in crop residues.