1. Akhtar, N., 2004 Agro-physiological response of spring sown sunflower (Helianthus Annuus L.) to various management practices. PhD thesis, Faisalabad, Pakistan: University of Agriculture.
2. Virtual water: A strategic resource, global solutions to regional conflicts;Allen;Groundwater,1998
3. Introduction to Energy Analysis;Blok,2006
4. Statistical review of World Energy 2007;BP,2007
5. Natural capital and sustainable development;Costanza;Conservation Biology,1992