How was irrigation connected to trade?

Irrigation was directly related to trading as a means of producing more goods than one farmer could need, allowing there to be a surplus of goods to trade. Water in the Middle East was a commodity and farming via taking water from streams and rivers was not only limited to where food could be produced but was also limited to when. With much less time and space to grow food pre irrigation much less was produced, only enough for the farmer and the immediate surrounding community.