Cheat Sophal, Duong Nguyen Khang, Preston T R and  Leng R A 2012 Methane emissions, feed intake and nitrogen retention in Yellow cattle given a diet of cassava root chips and fresh cassava foliage and either urea or potassium nitrate as source of NPN.  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/sophrua.htm