Uses compost, biological pest control, manure and crop rotation to create healthy produce. It avoids synthetic fertilisers and pesticides along with the use of growth hormones, antibiotics and genetic modification. The motivation behind organic farming is to create chemical free produce that is safe for consumers to eat, protect the long term health of the soil and minimize harm to farmers and other animals from farming activity. Organic farmers value crop diversity over highly specialized crops (known as a monoculture). A diversity of crops attracts a wider range of soil microorganisms and beneficial insects, improving the health of the ecosystem. It also reduces the risk of a particular species becoming extinct. Organic farmers also nurture the soil by adding compost and green manure and using techniques such as crop rotation and minimizing tilling. Tilling exposes soil to the air where it can lose carbon to the atmosphere. Weeds are controlled using physical rather than chemical approaches. These include tilling, mulching, cutting and using heat to kill weeds. Pests are controlled by encouraging beneficial predators and microorganisms and rotating crops to interfere with pest reproduction cycles. Companion plants are also used to ward off pests.