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.
9Koster H H,Woods B C,Cochran R C,et al.Effect of increasing proportion of supplemental N from urea in prepartum supplements on range beef cow performance and on forage intake and digestibility by steers fed low-quality forage.J.Anim.Sci.,2002, 80(6):1652-1662.
10Swingle R S,Araiza A,Urias A R.Nitrogen Utilization by Lambs Fed Wheat Straw Alone or with Supplements Containing Dried Poultry Waste, Cottonseed Meal or Area.J.Anim.Sci.,1977,45(6): 1435-1441.