Sustainable re-use of dairy cow manure as bedding and compost: Nutrients and self-heating potential

Dairy farm operations rely on a continuous supply of bedding material for cow comfort and hygiene. The re-use of liquid manure for this purpose has become possible after solid/liquid separation of the manure stream and 24 h processing of the separated solids through a tumbling drum composter. The finished bedding solids are reported to produce superior bedding to regular straw and the separated liquid stream can be retained as crop fertilizer. Off-farm export as bedding is only possible if the material is stable to prevent re-heating if bagged or piled. The nutrient value of the retained liquid and the quality of solids for export were investigated on a Canadian dairy farm by examining nitrogen and phosphorus distribution, as well as the self-heating potential of the composted solids. The effect of curing the solids for an additional 4 weeks during both summer and winter operations was evaluated. Results showed that the solids separation and 24 h drum composting process did not result in a compost that could be classified as mature and stable. However, further curing the solid product in ambient temperature piles for 4 weeks reduced compost re-heating from 26.2°C above ambient to 7.7°C (winter curing) and 3.8°C (summer curing). Nitrogen and phosphorus analysis revealed little difference between the liquid stream (post solid separation) and the incoming raw manure on a wet weight basis. The use of either of these products as plant fertilizer is similar and solid separation does not impact the agronomic value of the liquid manure.