Agricultural zones are the least profitable out of the three main industrial zones, as farms take a lot of space in order to develop.
Farms appear if the player zones a large enough low density industrial area (at least 8x8 tiles). Agriculture will not develop if pollution is too high. They also won't develop in dense industrial zones.
Agriculture has the same set of standards for developing like in SimCity 2000, but a no-cost ordinance called "Farmer's Market" has been added, which promotes agriculture and increases the number of farms.
Agriculture is the low-density industrial zone in SimCity 4. The player can zone bigger lots than other zones, and agriculture helps develop food for the city. Agricultural buildings also generate enormous amounts of water pollution, thus, it is highly recommended to place water pumps as far away from agricultural zones as possible, as water pumps will become polluted from the water pollution.