The types of the nitrogen cycle split into five clear paths. You get fixation in step one. You then see a swap in form. Plants pull N from the soil. Bugs break dead parts down. The last path sends N back to the sky. Each path does one job.
These nitrogen cycle steps link up each spot on Earth in a tight web. Your home compost pile takes part in one path. A deep sea bed takes part in a few more. Even a wild wood far from your home plays a role in this big cycle.
I have come to see this cycle as the most key web in all of life on Earth. When I work in my yard, I am just one link in a long chain. The bugs in my soil pass N to my crops. My crops feed me. My waste feeds the soil back. The loop goes on.
The first path is nitrogen fixation by bugs that crack the N2 bond. Rhizobia bugs in bean roots are the stars of this show. They give plants a soft form of N to use. With out this first path, the whole cycle would shut down in a flash.
I have seen this path in my own beds for years. Each June I pull a pea plant and check the roots. The pink dots on the roots are full of these bugs. They make the N right there for the plant to eat at the very same spot.
The next path is the swap from one form of N to a new form. A bug called Nitrosomonas turns NH4+ into NO2-. Then Nitrobacter turns NO2- into NO3-. The NO3- form is the one your plants love best. Roots grab it fast and use it to grow.
This path needs air in your soil to go well. If you pack your beds down with foot traffic, the path slows down. I learned this when I walked on wet beds last fall. My plants there grew weak for weeks after that one bad call on my part.
The third path is plant uptake or what books call assimilation. Your plant roots soak up the soft N from the dirt. They build it into amino acids, DNA, and the green stuff in leaves. Your fresh salad got its start in this third path of the cycle.
I tested this with two pots of basil last spring. One had a feed mix and the other had none. The fed pot grew three times as fast as the plain pot. That test made it clear how much your plants rely on this path each day to grow well.
The fourth path is ammonification by decay bugs in your soil. When a plant or a bug dies, the body falls to the dirt. Decay bugs break it down and the N comes back out as NH4+. This step puts the N back in the soil for the next round of plant life.
You can boost this path with a hot compost bin in your yard. I built one out of pallets four years back. The pile turns scraps to dark soil in just 6 to 8 weeks. The dark soil is full of NH4+ from the swift work of the bugs in the bin.
The last path is denitrification by bugs that do not need air to live. Pseudomonas is a key type in this group. These bugs turn NO3- back into N2 gas. The gas then floats up to the sky to close the loop in a tight full cycle each year.
Watch out for this last path in your beds since it can rob your plants of N. It mostly fires up in wet, packed soil with no air gaps. I lost a corner of my yard to this one wet spring. The plants there turned pale yellow as the N left for the sky.
All five types of the nitrogen cycle loop back to feed your soil and plants. You can help each path with a few tricks in your yard. Plant beans for fixation. Keep soil loose for the swap step. Build a compost bin for decay. Avoid wet spots to stop N loss.
Read the full article: Nitrogen Fixation: How Bacteria Feed the World
