What Is the Most Important Nutrient in the Soil for Growing a Plant?

For thousands of years, farmers used all sorts of different stuff to fertilize their crops. Nitrogen is the most important nutrient in the soil for growing a plant; things like legumes and manure add to it. More effort was put into reliably sourcing fertilizer for farming around the world. This resulted in things like horse manure being gathered from city streets,. Animal bones that were ground up into meal to spread across fields.