I know that we need more information like type of vegetation and surface area and weather but just consider a unit area like 1square m and optimum weather at equal conditions for both types of soil
Your question is some what confusing me. Irrigation water saving is not meaningful unless you haven't an idea about the crop water require ment. If you can apply a well scheduled irrigation applications according to the soil and crop parameters, both soils give same results. Only thing is, you have to appy direct amount of water for two soil types without wasting water, meaning, avoiding deep percolation loses in your specific case.