Can landfills turn to farm land?

No. The soil layer over the land fill itself is too thin to be useful for growing crops on. Also, a lot of garbage will be churned up with tillage. Not to mention a lot of hazardous material that may be found in the landfill may seep up through the soil into the plants which can make for either low yields or some very sick people. Landfills shouldn't be turned into pasture either because of these same hazards: garbage being turned up and hazardous wastes. Landfills are better off being turned into Golf courses, suburban areas or, in some areas, wildlife habitat. But never cropland.

Over a period of about 10,000 years, the landfill will probably decompose and settle into something that should be usable as farmland. However, many of these processes are not well enough understood yet to guarantee that this will happen, largely due to some of the materials which have been placed in the landfills.