NOVELTY - A composting additive comprising as a major component a cellulose-based material which has been chemically pre-treated to enhance the biodegradability of the cellulose where the additive is in the form of discrete pieces and has a relatively high carbon/nitrogen ratio is new.    USE - In the composting of organic matter having a relatively low carbon/nitrogen ratio (claimed).    ADVANTAGE - The chemically pre-treated major component such as cellulose-based material enhances the biodegradability of the cellulose contained. The shredded additive increases the porosity and lowers the bulk density of the compost thus protecting aerobic conditions.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) manufacture of the additive which involves:    (a) chemically treating a lignocellulosic material so as to remove at least a portion of lignin;    (b) shaping the treated material into discrete pieces; and    (c) applying a composting accelerator to the surface of the discrete pieces; and    (2) composting organic matter having a relatively low carbon/nitrogen ratio which involves:    (a) forming the organic matter into a heap; and    (b) adding to the heap a predetermined quantity of the composting additive so as to produce a heap having a balanced carbon/nitrogen ratio and optimized moisture content.    Preferred Features include the cellulose-based material being lignocellulosic material selected from barley, oat and wheat straws, wood chips, wood shavings, sawdust and paper. The additive also includes a composting accelerator comprising at least one enzyme (preferably a fungal enzyme). The enzyme preparation is derived from Humicola insolens having endo-1,4 beta-xylanase, beta-glucanase, cellobiase, hemicellulase and cellulase activities; Trichoderma reesei having cellulase activity; and Aspergillus niger having beta-glucanase, hemicellulase, pertinase or endoglucanase activities. The predetermined quantity of the composting additive is in an amount of 1 - 6 (preferably 3 - 5 or more preferably 2 - 4) kg per 10 kg of the organic matter. The cellulose-based material is one which has been chemically pre-treated to remove at least a portion of the lignin in the lignocellulosic material.