6Gonzdlez-Martin I,Hemdndez-Hierro J M. Detection and quantification of additives (urea,biuret and poultry litter) in alfalfas by nit spectroscopy with fibre.optic probe[J].Talanta,2008,76(5) :1130 - 1135.
7International Standard Organization. ISO 6654-1991. Animal feeding stuffs- Determination of urea content [S]. ISO, 1991.
8O'Keeffe M,Sherington J. Comparison of three methods for the determination of urea in compound feed and silage [J].The Analyst,1983,108 (1292) : 1374 - 1379.
