The present investigation was carried out in the farm of Nubaria Agricultural Research. Station during the two winter seasons 2016/2017 and 2017/2018 to study the effect of three surface irrigation treatments (I1=100%, I2= 80%, I3= 60% of ETp) and four potassium levels (control 0, 57.12, 114.24 and 171.36 K2O/ha) on fodder beet growth, physiological characters, productivity and forage quality under calcareous soil conductions. The main results were as follows:  1- Increasing irrigation levels up to 100% ETp led to significant increase in crop growth rate at the two periods (90-120) and (120-150 DAS), root diameter, leaf area per plant, root dry matter/ plant, root fresh weight/plant, total yield, crude protein percentage, digestive crude protein percentage, shoot K%, crude fiber percent and carbohydrate percent. There was insignificant difference between 100% and 80% ETp in leaves dry matter /plant, foliage fresh weight /plant, foliage yield (ton/ha) and K% in root. Whereas the total digestible nutrient percent and root length were significantly increased by increasing water stress. Medium treatment at 80% of ETp give the maximum values of water use efficiency (WUE). 2- Increasing potassium fertilization levels up to 171.36 kg K2O/ha significantly increased CGR at (90-120 and 120-150 DAS), root length, root diameter, leaf area, root dry matter /plant, leaves dry matter /plant, CP%, DCP%, CF% and carbohydrate % In root.  Adding 171.36 or 114.24 kg K2O/ha had insignificant differences in the first CGR period (90-120) DAS, root fresh weight (kg/plant), foliage fresh weight (g/plant), K% in shoot and root. TDN (%) decreased by increasing potassium fertilization levels. Maximum water use efficiency (WUE) was obtained when plants received 171.36 kg K2O/ha. 3- The interaction effect between water regime and potassium fertilization was found to be significant for CGR at the two periods, root length, leaf area/plant, leaves dry matter/plant, root and leaves fresh weight / plant, total yield, root yield, CP%, DCP%, K% in shoot and carbohydrate% in the combined analysis. The maximum value of WUE was obtained when plants were watered by 80% from ETp and received 171.36 kg K2O/ha.