Skip to content
Home » Gardening Tips

How To Add Nitrogen to Soil

How To Add Nitrogen to Soil

Like human beings, your plants also need micronutrients to grow fully. One of these essential micronutrients is nitrogen. Nitrogen, of course, is indispensable for the growth of plants! And plants need it to grow healthy and develop foliage. With the right supply of nitrogen, plants can achieve their healthiest growth. Plants can get this micronutrient from the soil.  

But garden soil is often lacking in nitrogen despite the abundance of it in the atmosphere. The fact—the earth’s atmosphere consists of 78% nitrogen. Yet, most plants are powerless in harnessing the abundant nitrogen in the atmosphere. Before they can use nitrogen, it must be first converted into nitrogenous compounds. This conversion process usually happens in the soil. 

Some microorganisms (diazotrophs) in the soil can synthesize nitrogen into useful nitrogenous compounds. Some plants like legumes can also synthesize nitrogen, and they do it in their roots. Moreover, lightning can cause the conversion of nitrogen and oxygen into nitric acid. The synthesizing and conversion process, however, is referred to as nitrogen fixation. 

Nitrogenous compounds are then absorbed by the roots of plants. Then, plants use these compounds for building carbohydrates, proteins, nucleic acids, and lipids. But to help plants get more nitrogen, the nitrogen content of the soil must be first improved.

The Value of Nitrogen to Plants

Nitrogen is essential to the growth and health of plants. It has several functions that enable plants to grow healthily. Here are its essential functions:

  • Nitrogen is an indispensable element in building amino acids. Amino acids, on the other hand, are the building blocks of protein that plants make.
  • Nitrogen is an essential component of nucleic acids. Nucleic acids, in turn, form the very DNA of plants and other living things. They also hold the genetic code of living things.
  • Nitrogen is an essential component of chlorophyll. Chlorophyll, on the other hand, gives a plant its green color. Hence, a plant with enough nitrogen will show vigorous growth. Moreover, photosynthesis is enabled when plants can get a high level of nitrogen.
Why Does Soil Lack Nitrogen

Why Does Soil Lack Nitrogen?

The lack of nitrogen in the soil is due to many factors. It may be due to the over-cultivation of soil that happens in overused farms. It can also be due to the presence of carbon-rich organic matter in the soil. Bacteria usually synthesize carbon-rich organic matter like sawdust. Yet, they typically use up the nitrogen in the soil to make this synthesis. This leaves the soil bereft of nitrogen. And this process is referred to as “Robbing the Soil of Nitrogen.” 

Other factors that can cause the loss of nitrogen in the soil include soil pH, soil temperature, denitrification, volatilization, and many other factors. Plants, however, exhibit symptoms that would let you know they lack nitrogen. These symptoms include the following:

  • When their leaves begin to turn into pale yellow color.
  • When the older leaves turn entirely yellow, this happens when plants can no longer make enough chlorophyll due to the lack of nitrogen.
  • When flowering and fruiting becomes scarce, this is usually due to inactive lateral buds and stunted growth due to the lack of protein.

Ways to Scientifically Determine the Soil’s Lack of Nitrogen

The abovementioned signs can also be symptomatic of a disease. It can also be signs of deficiency in some nutrients. Moreover, it can be caused by pest infestation or toxicity. Hence, to scientifically determine the cause of these symptoms, you should do the following quantitative test:

  • You can engage in soil testing to analyze the soil sample and find the health of the soil. You can do this by measuring the soil’s pH level and its nutrient content. You can do this annually or when the abovementioned symptoms appear in your plants.
  • You can also engage in a plant tissue test or chlorophyll content test. This is done to measure the chlorophyll content of your plant. This is because chlorophyll and nitrogen concentration are interrelated.

Understanding Nitrogen Fixation

Nitrogen fixation is a process of turning gaseous nitrogen into nitrogenous compounds. This process happens in the biosphere. It may be fascinating to imagine how this sub-molecular process happens. Yet, it does happen beyond the ability of our naked eyes to see. Here are several agents that occasion nitrogen fixation:

1) Nitrogen Fixation with the Help of Microorganisms

Nitrogen fixation can happen through the works of microorganisms. The result of this nitrogen fixation is ammonia (NH3) and other nitrogenous compounds. Ammonia is then metabolized by microorganisms to form other nitrogenous compounds. Plants use these fixed nitrogen compounds for synthesizing amino acids, proteins, nucleic acids. This process turns the useless nitrogen in the atmosphere into useful compounds. 

2) Nitrogen Fixation Can Also Happen When Lightning Flashes in the Sky

Lightning converts nitrogen and oxygen into nitrogen oxides. These nitrogen oxides then react with water to make nitric acid. Around 90% of fixed nitrogen, however, is fixed in the roots of the plants. 

3) Certain Plants Largely Contribute to Nitrogen Fixation

Nitrogen fixation happens in the roots of some plants like legumes. These plants contain bacteria in their root nodules that produce nitrogen compounds. These bacteria make use of sugars provided by the plants to turn nitrogen into ammonia.

Clover, soybean, kudzu, alfalfa, peanut, and pea also can engage in nitrogen fixation. When these plants die, they release their nitrogenous compounds into the soil. These compounds then become available to other plants. 

How to Improve Nitrogen Content in the Soil

How to Improve Nitrogen Content in the Soil?

If your garden soil lacks nitrogen, you can then apply the following methods for improving the soil. You can increase nitrogen in the soil via organic and non-organic methods: 

A) Non-organic Methods

You can increase the level of nitrogen in the soil via the use of synthetic fertilizers. These fertilizers are easy to apply and fast-acting. You can also buy them from your nearest plant nurseries to your home. You can apply these fertilizers during the growing season. You can also apply them when your plants suffer from nutritional deficiencies. Yet, synthetic fertilizers fade more quickly than organic fertilizers. And thus, you need to reapply them more often. 

When buying synthetic fertilizer, you should choose the one with the right NPK ratio. NPK ratio refers to the Nitrogen-Phosphorus-Potassium ratio. Non-organic fertilizers carry three numbers. You’ll see sometimes 10-10-10 ration. This means it has 10 percent nitrogen, 10 percent phosphorus, and 10 percent potassium. Others have 18-20-10 labels, while others have 15-13-20. Select the fertilizer with the correct labels. 

B) Organic Method

You can also increase the nitrogen content of the soil via organic means. This method slowly releases nutrients into the soil. This method can be done via nitrogen fixation. You can also do it by using composted manure and using composted soil. Lastly, you can also use animal manure, which is rich in nitrogen.

1) By Composted Manure

Manure of livestock and poultry are good sources of nitrogen. But fresh manure contains excessive nitrogen. This excessive amount of nitrogen can burn plants. It may also bear harmful bacteria that can cause plant diseases. 

So, you need to let fresh manure to age for six months. In this way, the nitrogen in it can be easily absorbed by plant roots. You should, however, mix aged manure with compost. In this way, you can avoid burning the plants. You can also add it to the garden soil in spring, 2 months before you plant that soil.

2) By Distributing Animal Waste!

Have you ever heard of aquaponics? I guess you did. This method involves planting the plants on grow beds and containers. The nitrogen-rich water coming from the fish tanks is made to flow into these grow beds. Fish waste, of course, contains a balanced mixture of nitrogen, phosphorus, and potassium. So, the plants can grow in aquaponics systems without the use of soil. They rely heavily on micronutrients coming from fish manure.

3) By the Use of Compost

You can also increase the amount of nitrogen in the soil by adding compost to the soil. You can compost organic matter that is rich in nitrogen. This organic matter includes fish emulsion and eggshells. It also includes plant waste like nuts, tea leaves, fruit rinds, corn cobs, and vegetable scraps. You can also add waste from your kitchen, garden trimmings, and grass clippings. Online, you can learn about the different methods of composting organic matters.


Nitrogen is indispensable to the healthy growth of plants. It may be abundant in the atmosphere, but the soil may lack it. So, to replenish the soil with nitrogen, you need to apply what you have learned in this article.

You’ll know if the soil lacks nitrogen if the plants exhibit the abovementioned symptoms. You can also figure out if the soil lacks nitrogen by employing soil tests. Lastly, you should be sensitive to your plants’ needs for like human beings; your plants need your care to grow healthy. 

Share this post on social!

Carlos Warren

Growing up in Texas, I was fascinated by the world of science and invention, thanks in large part to my father's work at Dow Chemical Company. However, my true passion lay in the natural world, and I became an expert in organic gardening and composting at a young age. I spent hours studying the microbiological communities in our family garden, using a microscope to define the quality of the soil. My love for farming and gardening led me to explore new techniques and methods, constantly pushing the boundaries of what was possible.