Agricultural practices lead to the emissions of several gases as well. The burning of forests and savanna grasses in tropical and subtropical regions to create pastures and cropland yields additional large amounts of carbon monoxide, methane and nitrogen ox- ides. Moreover, soil exposed after forests are cleared emits nitrous oxide, as do nitrogen-rich fertilizers spread over fields. The breeding of domestic animals is another major source of methane (from oxygen-shunning bacteria in the digestive tract of cattle and other cud-chewing animals), as Is the cultivation of rice, which is a staple food for many people in the tropics and subtropics