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How Nitrogen Works in Soil

By Jon Frank
This article first appeared in the July 2019 edition of Acres U.S.A. magazine.

Corn growers hold a special place in American agriculture. Corn is our largest crop, representing millions of acres under production. And farmers are the stewards of those acres. This is a serious responsibility and a massive opportunity to improve soil health on a significant proportion of American farmland.

As every corn grower knows, nitrogen is the most important nutrient for corn production. When it comes to corn yield, all other nutrients take a back seat. Field corn is a large plant — typically ranging from 6- to 8-feet tall and sown anywhere from 26,000 to 40,000 plants per acre. Yields today average from 150 to 300 bushels per acre. When you add up these three features — tall plants, high planting density and large yields — it’s no wonder corn requires a heavy dose of nitrogen.

High nitrogen rates enable excess nitrogen to run off into surface water and from there to aquifers. When nitrogen and phosphorous get into waterways, they stimulate the growth of algae. When this algae bloom dies and decomposes, it sucks up much of the oxygen out of the water, causing fish to die — especially game fish, which require higher oxygen levels.

It is here, at the intersection of agronomy and the environment, that every farmer walks a tightrope. Farmers have a fiduciary responsibility to make a profit, and profit requires a sizable yield. At the same time, farmers have a moral obligation to carefully steward the land they farm. Fortunately, most farmers are salt-of-the-earth folks who already feel this tension and want to do what is right.

In their defense, I do want to point out that nitrates are a natural form of water droplets pick up nitrates from the atmosphere and deposit free nitrogen into the soil. Because these nitrates come in small doses — 1-2 pounds per acre — plants pick them up quickly and virtually none escapes out of the root zone.

Nitrogen: It’s Complicated

Nitrogen is a peculiar element. Its home address is the atmosphere. Thus, its natural tendency is to find a way back home. It is in every breath of air we breathe and also in every single living cell. It is ubiquitous and rather mysterious. Nitrogen is a shape-shifter, easily changing from one form to another.

There are four main forms of nitrogen:

1. Nitrate (NO3) — Nitrate provides growth energy to corn, helping the plant build its infrastructure of stalks and leaves. Nitrates combine with many other elements, including a large number of trace minerals. This form of nitrogen is subject to leaching.

2. Ammonium (NH4) — This form of nitrogen, along with its close relative, urea, provides reproductive energy to corn. Reproductive energy promotes blossoms, flowers and pod set. Ammonial forms of nitrogen are subject to volatilization — the process in which nitrogen escapes the soil to return to the atmosphere. Combining nitrogen with growth energy and nitrogen with reproductive energy can suddenly release a lot of energy. This energy can be used both as an explosive and as a fertilizer for corn. Either way, it packs a lot of energy.

3. Amino Acid / Protein — This is the form of nitrogen made by biology. It can be produced in-house by soil microbes and growing plants, or by animals creating manure or fish harvested from the ocean. When nitrogen is in the amino acid or protein form, it will not leach or volatilize.

4. Humus — When soil biology combines an amino acid type of nitrogen with plant-available minerals in a carbon matrix, you get humus. Humus is reserve soil fertility — ready-to-use plant nutrients as soon as there is a need. Just like a well-stocked pantry.

Function in Soil

Nitrogen is the primary electrolyte in soil. This means that soluble nitrogen in soil increases electrical conductivity. In the human body we also have a certain balance of electrolytes in our blood and body fluids. These electrolytes carry weak electrical charges throughout our bodies.

In soils, electrolytes do the same thing. Having an adequate supply of electrolytes corresponds very closely with plant growth; or, to say it better, an adequate supply of electrolytes corresponds with nutrient availability, which drives plant growth. Nitrogen is not the only electrolyte. Other soluble nutrients or salts also conduct electrical charges.

By way of illustration, an electrical circuit has copper wires, which conduct electricity, and resistors, which moderate the flow of electricity. Soluble nutrients in soil conduct electrical charges just like a wire in a circuit. Humus and carbons moderate the electrical flow to make it suitable for plant uptake. Both functions are needed simultaneously.

As a point of clarification, any nutrient in soil, and many aspects of soil, can be looked at through various lenses. This is like having different kinds of glasses — each pair will illuminate objects differently. We can look at soil and nutrients through the lens of physics, chemistry or biology. It’s best to use all three to get a comprehensive view. Here is an example when looking at nitrogen:

• Physics — Nitrogen is an electrolyte that carries electrical charges that assist in nutrient delivery and plant growth

• Chemistry — Nitrogen is the center core of amino acids and proteins

• Biology — Soil biology builds amino acids through the microbial system

I will switch around between these various lenses. While nature works in all three realms simultaneously, I have to write in a linear fashion.

For corn growers there are two ways to apply nitrogen for its electrolyte function. Both methods work pretty well.

• Check soil EC (electrical conductivity) with a conductivity meter

• Guestimate based off experience from trial and error.

Most corn growers are not familiar with conductivity meters. But using one regularly throughout the season brings many revelations.

When soil has an adequate supply of available nutrients, and especially nitrogen, these nutrients carry an electrical charge. With a simple hand-held meter, farmers can measure the electrical conductivity of their soil. This reading is a de facto indicator of nutrient sufficiency.

The unit of measurement is micro Siemens per centimeter (µS/cm), or milli Siemens per centimeter (mS/cm). To convert between the two is simple; divide by 1,000 or multiply by 1,000. As an example, 0.36 mS/cm = 360 µS/cm. I prefer setting conductivity meters to auto range. This will default to readings of µS/cm. If the conductivity is above 2,000, it will then display as mS/cm.

I have found excellent corn growth when soil conductivity is around 700 µS/cm.

The more nutrients applied as fertilizer, the higher the conductivity reading. The more rainfall or crop uptake, the lower the conductivity. An over-application of fertilizer results in high or excessive conductivity.

A conductivity meter is an excellent diagnostic tool to help identify hidden nutrient deficiencies. When too little nitrogen is applied, yield suffers.

How to Take a Conductivity Reading

First make sure you have a meter with a direct soil probe. The old method of mixing half soil and half distilled water is accurate but way too cumbersome.

Neal Kinsey, Using Soil Analysis to Grow Crops, from the 2005 Eco-Ag Conference & Trade Show. (50 minutes, 12 seconds). Listen in as agronomist Neal Kinsey, the author of Hands-On Agronomy, teaches about how to test your soils, and use that data, to increase crop yield and decrease weed pressures.

I strongly recommend a meter with a 24-inch T-handle probe. This allows a quick check without having to squat to the ground. Next select a consistent location, such as 4 inches from the corn stalk. Be sure to have a regular depth. I normally suggest between 2 and 4 inches. Now take multiple readings across your field and average them together.

While the conductivity meter is incredibly valuable, there are a number of caveats to keep in mind.

• The higher the humus level, the more moderated conductivity readings become; i.e., less up and down swings. High humus generally lowers the base desired level.

• The healthier the soil, the more biology will provide the nutrition the crop needs in place of applied fertilizers. This lowers the desired conductivity level.

• A buildup of soluble non-nutrients such as sodium, chlorides and bicarbonates can impact the conductivity reading and raise the base desired level. The same applies to high conductivity irrigation water.

• The more the corn crop draws on nitrogen from humus and amino acid nitrogen, the lower the base level needs to be.

Consistently low conductivity indicates lost yield. A side dress or fertigation of liquid nitrogen or other soluble nutrients will immediately raise soil conductivity. In contrast, a foliar spray will not appreciably raise soil conductivity. Nutrients have to be in the soil, not on plant leaves, in order to raise conductivity.

Excessively high conductivity throughout the season indicates excess fertilizer application and the potential to leach nutrients out of the root zone into the subsoil. Very high conductivity levels are especially hard on germinating seeds and can burn roots if over 2,000 µS/cm.

If all of this seems too complex and overwhelming, now you know why most farmers and consultants use the tried-and-true method of calculating pounds of nitrogen applied throughout the growing cycle. It is so much easier — but there is a problem … no one agrees.

Ask a dozen crop consultants how much nitrogen a corn crop requires and you are likely to get at least a dozen answers and quite a few comments about desired yield. The answer to this question is every corn farmer’s dilemma: too much nitrogen is expensive for the farmer and expensive for the environment; too little nitrogen and you lose yield and thus profit.

Metrics are important in the economy, in business and on your farm. The most common metric everybody talks about is yield per acre. One of the most important metrics from a financial perspective is profit per acre. While this is a useful metric and should be tracked, it is a purely “Ebenezer Scrooge” kind of a number.

It is more inciteful to ask a deeper question: how many pounds of nitrogen are required for every bushel of corn I raise? The answer to this question gets to the heart of the corn farmer’s dilemma. Better soils and farming practices require less nitrogen per bushel.

Let’s say you broadcasted 100 pounds of monoammonium phosphate (MAP), 200 pounds of ammonium sulfate and 200 pounds of urea before planting. MAP is 11-52-0. The ammonium sulfate is 21-0-0, while urea is 46-0-0. All these numbers represent percentages. Thus, the “11” in 11-52-0 indicates 11 percent. This multiplied by the total amount of applied product gives the total pounds of nitrogen applied for that fertilizer. MAP (0.11 x 100) gives 11 pounds of nitrogen, the ammonium sulfate (0.21 x 200) provides 42 pounds and the urea (0.46 x 200) adds 92 pounds. Added up, this equals 145 pounds of actual nitrogen applied.

Let’s assume this farmer had read my earlier article on humus and had sprayed last year’s residue with 5 pounds of nitrogen as part of the residue spray for a nice even number of 150 pounds of total nitrogen applied. At harvest, this farmer averaged 200 bushels per acre.

Nitrogen Efficiency (NE) = pounds of N applied per acre divided by bushels of corn harvested per acre. Thus NE = 150/200 = 0.75. This farmer can say that for every bushel of corn, he applied ¾ of a pound of nitrogen. The inverse of this equation is also interesting. 200/150 = 1.33. This means that for every pound of nitrogen applied, the farmer harvested one and a third bushels of corn.

The Soil Works Podcast, by Glen Rabenberg, recommended for readers on this page. Listen in and learn how nitrogen can become available for your plants.

Nitrogen efficiency is at the very heart of the issue. It is actually the best metric to use when looking at overall efficiency of farming corn. Why? Because biological practices promote a healthy soil. A healthy soil supports a larger and broader diversity of microbial species in the rhizosphere that surround plant roots. This microbial system supports corn plants by predigesting soil amendments and rock minerals. As these additional nutrients and pre-made amino acids, derived from the dying off microbes, are taken up by corn plants, nitrogen efficiency increases. In other words, you get more corn with less nitrogen.

By pouring on excessive nitrogen, toxic agriculture can compete and win the bragging rights to yield per acre. But this comes at a very steep environmental cost. I also question this corn’s value as a feed ingredient. It is far better to focus on biological practices and use nitrogen efficiency as your main metric. And if we keep improving the health of the soil, the health of the microbes and nitrogen efficiency we should be able to compete on another metric: profit per acre.

Here is the place I must give a disclaimer. By improving the overall environment in your soil fertility program, you earn the right to use less nitrogen. Too many people have fallen for the half-truth that says, “Use this super-duper juice and cut your nitrogen in half.” Saves you a lot of money, right? And the scary thing is it might actually work for a couple of years. But eventually the Pied Piper has to be paid.

Super-duper juice products can work really well. And they may even be sold by very well-intentioned businesses. But without a zealous focus on the fundamentals — things like levels and ratios of available minerals, energy in the soil, full-spectrum nutrition, adequate NPK or sufficient calcium — things can crash and burn. Please don’t let that be you!

6 Ways to Increase Nitrogen Efficiency

Here are six ways to improve the health of your soil, the health of the microbial population and ultimately nitrogen efficiency.

1. Use Amino Acid / Protein Forms of Nitrogen

You don’t need all your nitrogen coming in this form. Just look for places they can be added. Products to use include legume green manure / cover crops, animal manure, liquid or dry fish, or compost. Unless produced on-farm, these products will be more expensive. In the chart for nitrogen efficiency it was listed that <0.15 was possible. This is not theoretical. It has been done numerous times, multiple years in a row. And if you are wondering about yield, it was consistently 200 bushels, all organic.

My longtime partner in International Ag Lab, Wendell Owens, made this profound discovery decades ago. Not only did he prove 200 bushels could be consistently harvested organically, he also demonstrated the greatest nitrogen efficiency I have seen to date. And it is so simple. Ready? Just side-dress 50 gallons of 5-1-1 liquid fish 6 inches over from the row of corn.

This fish is as thick as molasses but not so sticky. It will require a squeeze pump with all nozzles and filters removed. Use 3/8-inch to ½-inch tubing and dilute the fish 50:50 with water to make it flowable. That’s the complete nitrogen program.

So, let’s run the numbers and calculate the nitrogen efficiency. 5-1-1 fish weighs 9.5 pounds per gallon. 50 x 9.5 = 475 pounds. 475 x 5 percent = 23.75 pounds of actual N. NE = 23.75/200 = 0.12.

Wow – a nitrogen efficiency of 0.12!

With high-priced organic corn, this program penciled out. The nitrogen in the fish is 100 percent amino acid form. Low-nitrogen fish spiked with Chilean Nitrate to get t 5 percent N will not work this way because it is not an amino acid nitrogen.

Dr. Carey Reams taught that every living cell across all species of life has the same foundational formation. He called this the Primordial Cell. The center of every cell is life, but wrapped around that life are always these five elements: nitrogen, carbon, hydrogen, oxygen and calcium. Reams taught that every living cell has the same foundation, and from there various other elements and compounds are added according to its genetic instructions.

It is fascinating to note that amino acids have the exact same elemental components. Life may be absent, but the composition of elements is the same. It is also intriguing to consider that 0.12 lbs. of nitrogen is far less than the actual amount of nitrogen in a bushel of corn which is at least half a pound. Where did the remaining nitrogen come from? Here is my answer: Ask the trees of the forest where they got their nitrogen for their leaves and twigs.

2. Have a Reservoir of Nitrogen as Humus

Humus is fertility in a soil savings account with full liquidity. It can easily liquidate into its fertility components, including nitrogen. But if you look at most soil tests for corn, you find humus levels at the bottom of the barrel.

It is very useful to build up this “fertility bank account” during fall, winter and spring. During summer, withdrawals can be made to keep pace with corn’s rapid growth and intense nitrogen demand.

Having a reservoir of the humus form of nitrogen adds resiliency to your farming operation. And it allows for less overall nitrogen, thus increasing nitrogen efficiency. Check your soil reports. When you see 30 and above on humus, you are in great shape. If you are 10 or below, you do not have any appreciable reserve fertility in the humus form. Therefore, it must be fully supplied via applied nitrogen.

For ultimate success in building humus, avoid GMOs and especially Bt-traited corn. You also need to eliminate herbicides. Both practices hinder the humification process.

3. Fix the Cal:Mag Ratio to 7:1

One of the rules we follow at International Ag Labs is very simple: Create an optimum environment for roots and microbes. And nowhere is that more important than fixing your soil’s calcium-to-magnesium ratio.

On the soil test we promote, the original Morgan Test, the optimum calcium-to-magnesium ratio is 7:1. This ratio directly impacts soil physics, soil chemistry and soil biology. This ratio is easy to calculate: just divide the calcium by the magnesium. Because this number is so important, we put it on every soil test.

Gary Zimmer, Gaining a Working Knowledge of Calcium, from the 2002 Eco-Ag Conference & Trade Show. Listen to Gary Zimmer talk about how calcium drives the flow of other minerals and nutrients through the soil and plant, and how to measure and balance calcium levels in your fields.

When the Cal:Mag ratio is below 7:1, the magnesium pushes nitrogen out of the soil and back into the atmosphere as gaseous nitrogen. This represents a huge inefficiency! The lower the ratio, the more nitrogen is expelled from the soil, and the costlier it gets to raise corn in this field.

Have you ever farmed a sticky heavy soil with excess magnesium? If so, you will find corn always does poorly. Why? Because corn is a nitrogen-loving crop. However, soil physics are dissipating nitrogen back into the atmosphere. That means it will take more nitrogen just to get the same yield.

If you own a piece of ground like this with a calcium to magnesium ratio of 4:1 or less, you need to take two actions:

  1. Fix the Cal:Mag ratio to at least 6:1; and
  2. Quite growing corn on that field until the ratio is corrected.

A better crop would be one that produces nitrogen such as soybeans.

Make sure you use high-calcium limestone as your primary amendment to raise available calcium and correct the Cal:Mag ratio. Never use Dolomite on a soil with a low Cal:Mag ratio. Calcium nitrate, gypsum and soft rock phosphate can all contribute as supplemental calcium sources, but never as the primary source to raise available calcium.

4. Increase Soil Biology

Soil biology is an incredibly broad subject. Many books have been written on it. The bottom line for you as a corn grower is very simple. A large microbial population around corn roots is actually a biological fertilizer factory.

As microbes live, reproduce and die, they leave behind the protoplasm of their dead bodies. Along with many minerals, this also contributes a steady stream of pre-made amino acids. Plants pick up these amino acids. This saves the corn plant a tremendous amount of metabolic energy by not having to construct its own amino acids. By using biology to convert soil and atmospheric nitrogen into high-efficiency amino acid nitrogen, less overall nitrogen is required.

Please read the next sentence very carefully. The key focus is not soil biology … it is on creating the optimum environment for soil biology. And the optimum environment is always an automatic result derived from the level and ratio of available minerals.

If you follow the rule to create an optimum environment for roots and microbes, you will reap the reward of creating your own fertilizer factory right beneath your corn plants. To implement this really requires a change in mindset and budget allocation.

We all know budget is a limiting factor in corn production. The key is to move money away from high-priced GMO seeds and various toxic chemical applications and into fertility inputs that optimize the environment for soil biology. The key is to always start with the foundations: major minerals, secondary minerals, trace elements and even rare earth elements. Once these foundations are in place, things like microbial inoculants, biostimulants and foliar sprays really work well.

Gary Zimmer, Minerals for Healthy Soil, from the 2017 Eco-Ag Conference & Trade Show. (18 minutes, 56 seconds.) Listen in as agronomist Gary Zimmer, author of The Biological Farmer and Advanced Biological Farming, teaches why he puts these four minerals at the top of his priority list.

5. Spread Out Nitrogen Applications

A single large dose of commercial nitrogen is inefficient. By splitting up the nitrogen into several smaller doses, efficiency significantly increases. The exception to this rule is the use of amino acid/protein forms of nitrogen. They always maintain their efficiency.

In my opinion, the fiscal nitrogen budget for the next crop starts as soon as the current crop is harvested. This means that the fall residue program is the first small dose of nitrogen for the next crop. Additional applications can be made via:

  • Fall applications of manure or ammonium sulfate;
  • Incorporating N-producing legume crops;
  • Spring applied dry nitrogen as a broadcast;
  • Liquid or dry nitrogen in the starter, side-dress, or topdress;
  • Liquid nitrogen applied through pivot irrigation;

The key for increased nitrogen efficiency is to use multiple N applications over the growing season. This will allow you to safely reduce 5-10 percent of overall nitrogen use.

6. Modify All Liquid N Applications

Straight liquid nitrogen such as UAN 32 percent (Urea Ammonium Nitrate) is inefficient on two counts. It is a very useful tool in a farmer’s toolshed. And it is far superior to anhydrous ammonia — a toxic, but cheap, form of nitrogen that destroys humus and kills soil biology. It just needs a little tweaking to overcome its inefficiencies.

The first inefficiency is that nitrates are prone to leaching, while ammoniacal and urea forms can volatilize. The second inefficiency is more serious. Plants can pick up straight nitrogen like UAN, but to make amino acids and proteins they first have to add carbons to the nitrogen. To do this, plants cycle N up to plant leaves and then back down to the roots while they pick up additional carbons. This is repeated until the nitrogen has enough carbons to make amino acids and proteins. This is a terrible waste of metabolic energy in plants.

To help correct both inefficiencies in liquid nitrogen, simply add carbohydrates. The easiest way is to dissolve 2-3 pounds of dextrose per acre. I prefer dextrose because it is available, ships without water weight and dissolves much quicker than table sugar. You can also use molasses or various syrups at 1-2 gallons per acre.

I categorize all carbohydrates as energized carbons. This energy feeds soil microbes and improves plant metabolism. These carbohydrates also help reduce leaching and volatilization.

Look at liquid nitrogen as an opportunity to create an amino acid precursor. Do this by adding carbohydrates, sulfur and possibly calcium to the nitrogen base. Here is a typical application per acre:

  • 10-15 gallons liquid UAN
  • 2-3 pounds dextrose dissolved in water
  • 2-3 gallons ammonium thiosulfate or 2-3 gallons liquid Calcium Nitrate

For most soils use ammonium thiosulfate. For low calcium soils the ammonium thiosulfate can be replaced with liquid calcium nitrate. Don’t use both, since the mixture has issues with stability.

I want to leave you with 5 cultural practices and actions you can take to improve nitrogen efficiency on your farm:

  • Do the fall residue program on corn residue
  • Soil test and amend to fix the Cal:Mag ratio
  • Consider cover crops or manure applications
  • Always modify liquid nitrogen
  • Know your metrics

Every business has metrics and so should every acre of corn. Here are the top three metrics I suggest for corn production.

  • Profit per acre
  • Nitrogen efficiency
  • Reserve fertility = humus

Jon Frank is the owner of International Ag Labs (aglabs.com), based in southern Minnesota. He is a soil consultant with more than 20 years of experience and is the founder of Grow Your Own Nutrition (growyourownnutrition.com). This article first appeared in the July 2019 edition of Acres U.S.A..