Two field experiments were conducted at Aly Mubarak experimental farm, El-Bustan region during 2006 nd 2007summr seasons to study the response of sweet potato to two mycorrhiza, vesicular-arbuscular mycorrhizal (VAM) fungi treatments (w= inoculation with VAM and w0= non VAM) and four irrigation treatments (irrigation with amounts of water equals: I1=120%, I2=100%, I3=80% and I4=60% of crop evapotranspiration ETc ).
Results revealed that there were significant effects due to the interaction between the tested mycorrhizae and irrigation treatments on the production of sweet potato through the two growing seasons. The highest yields of sweet potato tuber were 10.742 and 10.425 ton/fed. in the two growing seasons, respectively, that obtained by inoculation with mycorrhizae and irrigation with amount of water equals to 80%of ETc. Also, the inoculation with mycorrhizae and irrigation with amount of water equals to 80% ETc (I3) gave the highest values of tuber sweet potato (number/plant, tuber weight, tuber length, tuber diameter and TSS. But, the inoculation with mycorrhizae and irrigation with amount of water equals to 120% ETc (I1) gave the highest values of leaf area, foliage weight and tuber phosphorus content of sweet potato.
The total amounts of applied irrigation water for the 80% ETc irrigation treatment of sweet potato were 65.0 and 67.3 cm. in the two growing seasons, respectively. The highest water utilization efficiency (WUtE) values were 3.93 and 3.69 kg tuber sweet potato per m3 irrigation water, in the first and second seasons, respectively, that obtained by inoculation with mycorrhizae and irrigation with amount of water equals to 80%ETc.