An experiment was conducted with maize for silage as a main irrigation culture in the experimental field of the Agricultural Institute – Stara Zagora. The following variations have been tested: variation 1 – no irrigation (sentinel); variation 2 – optimal irrigation, 80%-85% of FC (100% irrigation); variation 3 – Irrigation as variation 2 but with first irrigation cancelled; variation 4 – irrigation as variation 2 but with second irrigation cancelled; variation 5 – irrigation as variation 2, but with third irrigation cancelled. On the basis of a chemical analysis of the sudangrass forage for the raw protein content, FUM, FUG and PDI were defined. It was found that the highest yield of raw maize protein grown as the main crop was obtained from the optimal irrigation variation, both in the non-fertilized and the fertilized variation, respectively with 1023.5 kg / ha and 1303.5 kg / ha. The optimal water supply of maize provides the highest energy efficiency of the forage expressed in FUM -15022.8 kg / ha, FUG -15584.4 kg / da, PDI – 1060 kg / ha for non fertilized variations and FUM -16873.5 kg / ha, FUG -17516.3 kg / ha, PDI-1219 kg / ha with fertilizer applied.