Effects of straw, sawdust and sand bedding on dairy manure composting

Composting is an increasingly popular manure management tool for dairies. However, there is little information on the effects of common amendment and bedding types (straw, sawdust and sand) on windrow size, mass, volume, dry matter, and nitrogen losses during composting. In this study, straw, sawdust and sand bedded dairy manures were amended with either sawdust or straw and composted on multiple occasions. Results showed that starting windrow volumes for straw amended composts were 2.1 to 2.6 times greater than for sawdust windrows. Straw amended composts had lower initial bulk densities and temperatures, higher free air space values (75-93%), and near ambient interstitial oxygen concentrations during composting as compared to sawdust amended composts. Sand bedding resulted in greater compost densities, less weight loss and >50% more final compost on a per cow basis. All sawdust-amended composts self-heated to >55°C within 10 days. Sawdust composts without sand maintained these levels for more than 60 days meeting pathogen reduction guidelines. However, none of the straw-amended or sand bedded sawdust amended composts met the guidelines. All of the composts were stable after 100 days and exhibited manure volume and weight reductions relative to the initial manure. Initial compost C:N ratios ranged from 25:1 to 50:1 and the manure nitrogen lost during composting ranged from 2% to 38%. There was a negative correlation between initial compost C:N ratio and nitrogen loss (R ²=0.59). An initial C:N ratio of greater than 40 resulted in nitrogen losses less than 10% during dairy manure composting with all three bedding types.