Physical changes during active and passive composting of beef feedlot manure in winter and summer

There is increased interest in composting as a means of handling the large amounts of manure generated by southern Alberta feedlots. However few studi es have been conducted on the changes in physical properties of manure as i t becomes compost and the impact of these changes on haulage requirements. Additionally, there is a perceived constraint to overwinter composting in s outhern Alberta, due to extremely low air temperatures. This study examined active (mechanically turned) and passive (passive aeration system) windrow composting during winter and summer. Dry matter mass reductions were in th e range of 21-30%. Bulk density increased 3-4 fold with both types of compo sting. Volume loss during the thermophilic phase was of the order: summer-a ctive (72%) > summer-passive (55%) > winter-active (51%) > winter-passive ( 34%) with further smaller losses during the curing phase. Water mass loss w as as high as 83% for active composting during summer. Active composting ge nerally led to larger changes in physical properties of manure than passive composting. Winter composting was feasible despite ambient air temperature s < -30 degrees C. The results demonstrate the ability of composting to sub stantially reduce the mass, volume and water content of manure that needs t o be transported for land application. (C) 2000 Elsevier Science Ltd. All r ights reserved.