Understanding Our Soil: The Nitrogen Cycle, Fixers, and Fertilizer

peas beans and clover are among the 18 000 species in the pea family most species in this family including these three are known as nitrogen fixers they increase the level of nitrogen in the soil which plants need to produce proteins so they can grow and chlorophyll so they can photosynthesize one way to use this in the garden is to interplant nitrogen fixers with other plants that need a lot of nitrogen or you could plant a nitrogen-fixing cover crop like clover for fertile soil next year okay this can be useful but doesn't nitrogen fertilizer do the

same thing but more conveniently why bother with this nitrogen fixation thing understanding this requires us to understand how nitrogen fixation works which in turn requires us to understand the broader nitrogen cycle so let's start with the big picture nitrogen makes up 78 of the earth's atmosphere by volume but most of this nitrogen takes the form of two nitrogen atoms strongly bonded together which isn't very reactive and is useless to plants for it to become plant available we need the help of bacteria various species of bacteria eat atmospheric nitrogen and poop out ammonium this gets eaten

by other kinds of bacteria which poop out nitrite which gets eaten by yet another kind of bacteria which poops out nitrate all of these forms of nitrogen are available for plants especially nitrate which is the easiest for plants to use plants can take this up directly if it is near their roots but they most often rely on strands of fungi that attach to their roots and bring nutrients to them in exchange for the sugars and carbohydrates the plant roots exude dead plant material is also rich in nitrogen and gets brought down with the help of

worms whose poop is a delicacy among nitrifying bacteria some of the ways nitrogen exits the soil is when the crop is harvested when water carries it away or when it becomes gaseous and returns to the atmosphere or if the soil lacks oxygen different anaerobic bacteria grow which convert nitrates back into atmospheric nitrogen notice that these things only happen with loose nitrogen in the soil not with nitrogen inside organisms okay so we know that the nitrogen cycle depends heavily on life in the soil without them the plants would be quite sad but you may have noticed

if the fixation process is done by bacteria where do nitrogen-fixing plants fit into this believe it or not nitrogen-fixing plants don't fix nitrogen rather they create habitat for the bacteria that do the roots of this clover plant have little nodules that house huge amounts of nitrogen-fixing bacteria the ammonium that these bacteria create slowly releases into the soil for neighboring plants and microorganisms to use when the plant dies the bacteria disperse into the soil resulting in an abundance of bacterial allies for future plants nitrogen needs you know how earlier i said that water can carry soil

nitrogen away this nitrogen ends up in rivers which can disrupt the ecosystem by enabling algae to dominate but remember this only happens to lose nitrogen in the soil and not nitrogen embedded in organisms and fertilizer adds pure nitrogen without the organisms so when it rains huge amounts of it runoff and pollute the water loose nitrogen molecules are also much more prone to volatilization releasing huge amounts of nitrous oxide a potent greenhouse gas into the atmosphere but that's not all such quantities of pure nitrogen irritate earthworms which end up dying or leaving it disrupts the helpful

fungus on plant roots and changes the soil ph making it inhospitable to bacteria in short it kills the soil when the nitrogen all gets used up or washes away the organisms aren't there to help the plants get more so now you have to add more fertilizer which worsens the problem and these organisms did much more than just supply nitrogen the root fungi also brought up important minerals for the plants and now that they're gone mineral fertilizer must also be used instead of working with this self-sustaining web of organisms freely sharing nutrients we have to spend

more money to add loads of fertilizer to dead soil poisoning the water and contributing to climate change considering the inability of dead soil to supply plants with nutrients it's no wonder that throughout the last century vegetables have been steadily declining in nutritional value healthy food requires healthy soil so if the soil around you is rich and alive try to keep it that way but if like most of us the soil around you is dead or dying nitrogen fixers can help to add a little more life so that someday our tiny allies under our feet will

come back you