All contracts made between owners of land, their agents, administrators or executors, and laborers shall be witnessed by one or more disinterested persons and, at the request of either party, shall be duly executed before a magistrate who shall read and explain it to the parties. Such contracts shall clearly set forth the conditions upon which the laborer or laborers are engaged to work, embracing the length of time and the amount of money to be paid and when and, if it be on shares of crops, what portion of the crops.