Fossil fuel emissions are relatively easy to understand. If someone pulls coal, oil, or gas out of the ground and burns it, then they warm the earth. If they leave it in the ground, then they don't.
Agriculture is more complicated because it both absorbs and emits a lot of greenhouse gas. Every year, crops absorb about 17 gigatons (GT) of carbon from the atmosphere through photosynthesis, which is almost double the 9.4 GT emitted by burning fossil fuels.