geographer chai yangwei, in the green, follows these farmers to see how they cope with such low rainfallpeculiar to agriculture in this area, these are called "stone fields." a thin layer of stones is spread over the surface of the field to hold in moisture. stone fields can be used for about eight years. constant upkeep is necessary, however. this plot is two years old. the farmers are adding fertilizer. if the soil becomes mixed with the stones, the efficiency of a stone field decreases, so stones must be carefully swept aside. the next step is to dign cow manure. finally the stones will be spread back. melons will be grown here for the modern city nearby. lanzhou is home to 2.6 million people. its historical geography holds clues to the future of western china. today lanzhou is the second-largest city in china's northwest and the capital of gansu province. sowhis this city here? its growth is largelthe result of 20th-centurycentral. buwhat ipired e communists its to develop lanzhou? result imagine the chalngefor mal trying to link core areas in t east with the western frontier provinc