Composting Principles
Dry, high-carbon
amendment
Bulking agent with
large firm particles
Moist, high-nitrogen
primary ingredient
The proper proportion of the material to be composted combined with amendments, and bulking agents is commonly called the compost mix or the “recipe”.
A composting amendment is any item added to the compost mixture that alters the moisture content, carbon:nitrogen ratio (C:N), or pH.  Crop residue, leaves, grass, straw, hay, and peanuts hulls are examples of the material suitable for use as a compost amendment..
A bulking agent is used primarily to improve the ability of the compost to be self-supporting or have structure, and to allow internal air movement.  Wood chips is an example of bulking agent.  Some bulking agents may alter the moisture content and/or C:N ratio.  This type of material would serve as both an amendment and a bulking agent.