Cheat Sophal, Duong Nguyen Khang and Preston T R 2012 Methane emissions, feed intake and nitrogen balance in cattle fed cassava root chips and fresh cassava foliage with NPN from potassium nitrate or urea.  Proceedings of the International Conference "Livestock-Based Farming Systems, Renewable  Resources and the Environment", 6-9 June 2012, Dalat, Vietnam (Editors: Reg Preston and Sisomphone Southavong) http:/www.mekarn.org/workshops/dalat2012/html/sophal..rua.htm