How do agricultural activities contribute to global warming?

Well say you plant a small garden, you use fertilizer that contains a pesticide or a chemical that can infect you water system, eventually the water returns to the clouds and becomes acid rain. Said acid rain, eats away at the ozone level and contributes to global warming. But on the other hand lets say in your small garden you use natural fertilizer such as compost. In that example you are using waste to create and you are also helping prevent acid rain, because in that garden the nutrients are absorbed into the plants and no bad chemicals are returning to the water. Not only saving some fish in the process but helping to reduce the work of the factories that make artificial fertilizer and if they don't have work then the factory will reduce or close, therefore not producing toxic admissions. Another example would be using corn or methane for gas which is agriculture because of the farmers who grow said corn. In that example you are reducing toxic gases from the burning of fossil fuels. Also another thing, using wood from local farmers to burn in wood fires or stoves for heat cut down on the use of your heater saving the world once again from toxic admissions.