Amaranthus is one of the forage plants resistant to environmental stresses. This experiment conducted 2 years in form of a complete random block design based on factorial a with three replications, 3 levels of irrigation (irrigation after depleting 40, 60 and 75% of available water) as the first factor and organic (cow manure and phosphate-2), chemical (phosphorus and nitrogen), integrated and control (no fertilizer) fertilizer systems including was the second factor. The results of this study showed that crude protein, digestibility of dry matter, water-soluble carbohydrates, digestible nutrients, relative nutritional value and specific energy of lactation, due to the application of different fertilizer systems in each irrigation level were improved compared to of non-consumption of fertilizer. The performance of biomass and forage protein were increased by 38.89 and 54.37%, 30.60 and 41.23% and 22.20 and 34.92% in optimal, moderate and severe stress conditions respectively in integrated fertilizer system than the control treatment. The results of this study showed the use of organic fertilizers alone or combined with chemical fertilizers improved quantitative and qualitative traits of amaranthus forage irrigation after depleting 40 and 60% of available water. So, optimal use of biological inputs for sustainable agriculture and reduction of pollution caused by the use of chemical fertilizers is recommended.