Broadbent, F.E. (1981) Methodology for Nitrogen Transformation and Balance in Soil. Plant and Soil, 58, 383-399.
 Le Gouis, J., Béghin, D., Heumez, E. and Pluchard, P. (2000) Genetic Differences for Nitrogen Uptake and Nitrogen Utilization Efficiencies in Winter Wheat. European Journal of Agronomy, 12, 163-173.
 Ma, B.L. and Dwyer, L.M. (1998) Nitrogen Uptake and Use of Two Contrasting Maize Hybrids Differing in Leaf Senescence. Plant and Soil, 199, 283-291.
 Kamoshita, A., Muchow, R.C., Cooper, M. and Fukai, S. (1998) Genotypic Variation for Grain Yield and Grain Nitrogen Concentration among Sorghum Hybrids under Different Levels of Nitrogen Fertiliser and Water Supply. Australian Journal of Agricultural Research, 49, 737-747.
 Zegeye, T., Taye, G., Tanner, D., Verkuijl, H., Agidie, A. and Mwangi, W. (2000) Adoption of Improved Bread Wheat Varieties and Inorganic Fertilizer by Small-scale Farmers in Yelmana Densa and Farta Districts of Northwestern Ethiopia. Ethiopia.
 Anwar, M. (1988) Physiological Aspects of Grain Development in 2 Wheat Varieties as Influenced by Nitrogen Application. M.Sc. Thesis, Deptt. Crop Physiology, University of Agriculture, Faisalabad.
 Geleto, T., Tanner, D.G., Mamo, T. and Gebeyehu, G. (1995) Response of Rain Fed Bread and Durum Wheat to Source, Level, and Timing of Nitrogen Fertilizer on Two Ethiopian Vertisols. I. Yield and Yield Components. Communications in Soil Science and Plant Analysis, 26, 1773-1794.
 Mae, T. (1997) Physiological Nitrogen Efficiency in Rice: Nitrogen Utilization, Photosynthesis, and Yield Potential. In: Ando, T., Ed., Plant Nutrition for Sustainable Food Production and Environment, Kluwer Academic Publishers, Dordrecht, 51-60.
 Gasper, I. and Zama, E. (1990) Studies of the Variability, Inheritance and Correlation of the Main Quantitative Characters in Some Forms of Rye with Short Stature. Wheat, Barley and Triticale Abstracts, 9, 239.
 Chaudhry, A.U. and Mehmood, R. (1998) Determination of Optimum Level of Fertilizer Nitrogen for Two Varieties of Wheat. Pakistan Journal of Biological Sciences, 1, 351-353.
 Donmez, E., Sears, R.G., Shroyer, J.P. and Paulsen, G.M. (2000) Evaluation of Winter Durum Wheat for Kansas. Kansas State University Agricultural Experiment Station and Cooperative Extension Service, Publication No. 00-172-S.
 Soon, Y.K., Brandt, S.A. and Malhi, S.S. (2006) Nitrogen Supply of a Dark Brown Chernozem Soil and Its Utilization by Wheat. Canadian Journal of Soil Science, 86, 483-491.
 Slafter, G.A. and Andrade, F.H. (1989) Genetic Improvement in Bread Wheat (Triticum aestivum) Yield in Argentina. Field Crops Research, 21, 289-296.