The main methods of nitrogen fixation are four. You get the kind that bugs do on their own in the soil. You also get the kind that bugs do as a team with plant roots. You add to that the kind that lightning does in the sky and the kind that we do in plants.
I first saw this split in a soil class in school and it stuck with me for years. The teacher drew a pie chart on the board. Two of the slices were huge and the rest were small. That chart still shapes how I think about my own soil today.
The first path is biological nitrogen fixation by free bugs in your dirt. These bugs live on their own and pull N2 from the air gaps. They give plants about 122 million tons of N each year. You do not need to lift a finger for this gift.
I love this group since they work in the dark and you never see them. But your peas and your grass would die with no help from them. They prove that the most key jobs in life can hide from view in plain sight all the time.
The next path is symbiotic nitrogen fixation in the roots of beans, peas, and clover. Here, the bug and the plant trade gifts as a team. The plant feeds the bug sugar. The bug feeds the plant a form of N. I found this trade in my own beds last June.
You can spot this swap by pulling a pea or a bean plant from your soil. The roots will have pink bumps on them. Each bump is a tiny home full of bugs called rhizobia. Crack one open and the pink color shows the trade is going strong.
The third path is industrial nitrogen fixation in big plants we built. The Haber-Bosch route runs at 200 to 400 atm of force. It also heats the gas to about 500°C (932°F) to split N2 by brute force. This path is hot, loud, and rough.
This human path gives us about 120 million tons of N each year. That sits close to what all the soil bugs make. The bag of plant food from this path feeds about half the folks on Earth. You eat its yield each day.
The last path is atmospheric nitrogen fixation by big bolts in storms. Lightning rips N2 apart in the sky and the bits fall to soil as a form of N. This path makes just 5 to 10 million tons of N each year on our whole world.
I once read my rain gauge after a big storm and saw my plants green up the next week. That small lift came from N made in the sky. The boost is small per storm but adds up over a long warm season in your yard.
Each of these main methods of nitrogen fixation plays a role for one group or one place. You and other home folks should lean on the bugs in your dirt. Plant beans, peas, and clover to tap free N and skip the cost of a bag at the store.
Big farms lean on the human path to grow corn and wheat at scale. All of us lean on bolts to feed wild lands. All four paths feed the soil that grows your food and mine.
You can make the most of this in your own yard with a few easy steps. Plant a row of beans next to your tomatoes each year. Mix clover into your lawn seed in the fall. You can also rotate pea crops with your corn or your squash.
I have tried all three of these tricks in my own beds and they all paid off well. My corn rows that came after a clover cover gave 30% more ears than my plain plots. You can test this in your own yard with one small bed this year.
Each of the four paths feeds the same big system. Your soil, your air, and your plants all need a steady flow of N to grow. When you know how each path works, you can plan your beds with much more skill and care.
Read the full article: Nitrogen Fixation: How Bacteria Feed the World
