Biological processes contribute what share of the nitrogen used in agriculture?

1. Nitrogen reaches crops either through biological fixation or through chemical fertiliser. 2. Biological processes contribute 65 percent of the nitrogen used in agriculture. 3. That leaves the remainder to industrial routes, which draw on a nonrenewable resource such as natural gas. 4. So biological fixation is the majority contributor, which rules out the two values below half. 5. Using rhizobia is therefore a natural and environmentally friendly way to fertilise plants. 6. It also leaves some biologically available nitrogen in the soil after the crop, which is why legumes feature in rotations. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 31 "Soil and Plant Nutrition", section 31.3 Nutritional Adaptations of Plants_