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 26.2C above ambient to 7.7C (winter curing) and 3.8C (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.