Effects of age of cattle, turning technology and compost environment on disappearance of bone from mortality compost.
Stanford, K.I.M., Hao, X., Xu, S., McAllister, T.A., Larney, F.J., and Leonard, J.J. (2009). "Effects of age of cattle, turning technology and compost environment on disappearance of bone from mortality compost.", Bioresource Technology, 100(19), pp. 4417-4422. doi : 10.1016/j.biortech.2008.11.061
As residual bones in mortality compost negatively impact subsequent tillage, two studies were performed. For the first study, windrows of mature cattle or calves were placed on a base of barley straw and covered with beef manure. Windrows were divided into 2 sections and turned at 3 month intervals. Approximately 5000 kg of finished compost per windrow was passed through a 6 mm trommel screen, with bones collected and weighed. Bone weight was 0.66 % of mature cattle and 0.38% of calf compost on a dry matter basis, but did not differ after adjustment for weights of compost ingredients. In a subsequent study, four windrows were constructed containing mortalities, straw and beef manure (STATC) or straw, manure and slaughter waste (STATW). Also, straw, beef manure and slaughter waste was added to an 850 L rolling drum composter; DRUMW). Fresh bovine long bones from calves were collected, weighed and embedded in the compost. Bones were retrieved and weighed when windrows were turned, or with DRUMW, after eight weeks. Temperatures achieved followed the order STATW> STATC>DRUMW (P < 0.05). Rate of bone disappearance followed a pattern identical to temperature, with the weight of bones in STATW declining by 53.7% during 7 wk of composting. For STATC, temperatures were uniform over three composting periods, but bone disappearance was improved (P < 0.05) when compost dry matter was lower (46%), as compared to 58%. Using a ratio of 5 parts manure to 1 part mortalities, results of this study demonstrate that residual bone is < 1% of cured cattle compost and may be reduced by maintaining a high compost temperature and moisture content.