1. ARC (Agricultural Research Council), 1980. The Nutrient Requirements of Ruminant Livestock. Commonwealth Agricultural Bureaux, Slough.
2. Assefa, A., 2005. Farm Management in Mixed Crop-Livestock Systems in the Northern Highlands of Ethiopia. Ph.D. Thesis, Wageningen University, Wageningen.
3. Atsbi World Vision, 2004. Atsbi World Vision climatic data (2000–2004), Atsbi.
4. Long-term changes in soil organic matter under conventional tillage and no-tillage systems in semiarid Morocco;Bessam;Soil Use And Management,2003
5. Boons-Prins, E.R., De Koning, G.H.J., Van Diepen, C.A., 1993. Crop-specific simulation parameters for yield forecasting across the European Community. Simulation Reports CABO-TT No. 32, Group Plant Production Systems, Wageningen University, Wageningen.