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Nitrogen: Top 5 Things You Need to Know


An essential nutrient. Big number 7 (or 14.007). Healthy plants often contain three to four percent of this nutrient in above-ground tissue, and now, we’re uncovering what happens below the surface. Let’s talk nitrogen.

1. There are 3 forms of nitrogen in soil

With how much nitrogen is needed and utilized by plants, it only makes sense that it comes in multiple forms. Nitrate (NO3-) and ammonium (NH4+) ions and organic nitrogen compounds all exist within the soil, but only 1-5% of this nutrient is readily available to the plant. Organic nitrogen compounds make up 95-99% of soil nitrogen, but they require the help of microorganisms and beneficial bacteria to be utilized by the plant. Don’t worry, though. We’ve got the keys to unlocking this nitrogen mine.

2. Each form has a unique set of plant and nutrient interactions

The general nitrogen cycle flows through the processes of fixation, mineralization, nitrification, leaching, plant assimilation, ammonia volatilization, denitrification and immobilization. Depending on the conditions of your environment and your supplemental nitrogen application, you may see an individualized chain of reactions in your fields.

Fixation, mineralization and nitrification are all necessary steps to naturally supply your soil with nitrogen. After these, things can get tricky as the next processes can cause nitrogen loss in the soil.

Changes in pH levels can cause ammonia in the soil to be lost as a gas, or ammonia volatilization. This is most commonly seen with applications of fertilizers containing urea, which decomposes to ammonium in the soil. Loss from ammonia volatilization varies greatly, from no loss to 50% or more of applied nitrogen. Moisture of at least ½ inch, whether through rainfall or irrigation, moves urea far enough in the soil to minimize loss from volatilization.

Nitrogen leaching is another concern, and nitrate is the most susceptible form. Nitrate’s water solubility, mobility and abundance give it this characteristic. Once leaching reaches below four to six feet, there is little chance of recovery by most crops, unless they are deep rooted, such as alfalfa.

While not specifically a loss, immobilization is another obstacle for plants in uptaking and utilizing nitrogen. This is a temporary issue, but does prevent nitrogen access for a period of time. Placing fertilizers below crop residues, rather than in the soil with residue can help minimize immobilization.

3. Nitrogen deficiency is common, and quick to identify

Being one of the most highly-needed nutrients in plants and soil, it can be hard to maintain sufficient nitrogen levels. Luckily, it’s not hard to spot crops that are in distress due to a significant nitrogen deficiency. Common signs are pale/yellow-ish green plant color (due to decreased photosynthesis), inhibited plant growth and withering leaves, turning plant leaves from a yellow-ish green color to brown. However, soil and tissue sampling are still the most accurate, specific and reliable forms of determining nutrient levels.

Utilize Agronomy 365’s in-season soil and tissue sampling to get real-time data on nitrogen levels throughout your fields to help guide your crop nutrition decisions. You can make guesses by looking closely at the crops in your fields, but when it comes to inputs, your dollar goes a lot further when you’re focusing on the nutrients your crop truly needs, not the nutrients you think your crop needs.

4. Microorganisms help boost nitrogen uptake in plants

Microorganisms are the key to taking organic nitrogen compounds in the soil from molecules that are just taking up space in the ground to essential nutrition for your growing plants. First, it’s important to determine the current nutrient levels and needs of your crops, then design your crop nutrition strategy.

If your plants could benefit from utilizing more of the nitrogen that’s already present in the soil (especially when nitrogen markets have been so volatile), check out these BW Fusion products that increase nitrogen uptake and solubility:

5. Carbon and nitrogen must be carefully balanced for microbial activity

Microbes need a good carbon to nitrogen ratio to stay active in the soil. Ideal microbial C:N ratios are 5:1 for bacteria and 27:1 for fungi. In order to stimulate both simultaneously along with the crop, 12:1 is the perfect C:N ratio. Just like all nutrients, soil and tissue sampling is the best way for you to know the ratio found in your fields to help you make adjustments to reach this magic number.

Microbes become dormant when the ratio dips too low, and plants become nitrogen deficient when the ratio is too high. Anytime the carbon levels are greater than 12:1 in the soil, nitrogen becomes held up and is not released as well from the soil to the plant. When this occurs, it is best to band N and apply more during the beginning of the season to ensure N availability.

As C:N increases, it tells us if the soil’s carbon levels can support and hold onto N for later season needs. If the C:N ratio is narrow, it tells us the amount of N applied should be available to the crop soon after application.

There you have it, nitrogen in a nutshell. We could go on for days about this essential nutrient, so give us a shout if you want to talk nitrogen and see how we can maximize your nitrogen efficiency.

Nitrogen: An essential nutrient