Read this: As is known from the "Sumerian Farmer's Almanac", after the flood season and after the Spring Equinox and the Akitu or New Year Festival, using the canals, farmers would flood their fields and then drain the water. Next they made oxen stomp the ground and kill weeds. They then dragged the fields with pickaxes. After drying, they plowed, harrowed, and raked the ground three times, and pulverized it with a mattock, before planting seed. Unfortunately the high evaporation rate resulted in a gradual increase in the salinity of the fields. By the Ur III period, farmers had switched from wheat to the more salt-tolerant barley as their principal crop.

When did farmers switch from barley to wheat?
What is the answer? (If it cannot be answered, return "unanswerable")
unanswerable