Nitrogen (N) is essential for plant growth and is part of every living cell. It plays many roles in plants and is necessary for chlorophyll synthesis. Plants take up most of their N as the ammonium (NH4+) or nitrate (NO3-) ion. Some direct absorption of urea can occur through the leaves, and small amounts of N are obtained from materials such as water-soluble amino acids.

Quick Facts

Nitrogen is a component of vitamins, amino acids and energy systems within the plant, which form its proteins. Thus, N is directly responsible for increasing protein content in plants.

Quick Facts

Lack of N and chlorophyll means the plant will not utilize sunlight as an energy source to carry on essential functions such as nutrient uptake.

Quick Facts

Nitrogen is necessary for chlorophyll synthesis and, as a part of chlorophyll molecules, is involved in photosynthesis.

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Nitrate is very mobile in the soil and moves with soil water to root surfaces for plant absorption.

Dig Deeper

Healthy plants often contain 3 to 4 percent nitrogen in their above-ground tissues. This is a much higher concentration compared to other nutrients. Carbon, hydrogen and oxygen, nutrients that don’t play a significant role in most soil fertility management programs, are the only other nutrients present in higher concentrations.

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Nitrogen surrounds all plants in our atmosphere. In fact, every acre of the Earth’s surface is covered by thousands of pounds of this essential nutrient, but because atmospheric gaseous nitrogen presents itself as inert nitrogen (N2) molecules, this nitrogen isn’t directly available to the plants that need it to grow, develop and reproduce. Despite its identity as one of the most abundant elements on Earth, deficient nitrogen is probably the most common nutritional problem affecting plants worldwide.

Healthy plants often contain 3 to 4 percent nitrogen in their above-ground tissues. These are much higher concentrations than those of any other nutrient except carbon, hydrogen and oxygen — nutrients not of soil fertility management concern in most situations. Nitrogen is an important component of many important structural, genetic and metabolic compounds in plant cells. It’s a major element in chlorophyll, the compound by which plants use sunlight energy to produce sugars from water and carbon dioxide, or, in other words, photosynthesis.

Nitrogen is also a major component of amino acids, the building blocks of proteins. Some proteins act as structural units in plant cells, while others act as enzymes, making possible many of the biochemical reactions on which life is based. Nitrogen appears in energy-transfer compounds, such as ATP (adenosine triphosphate), which allows cells to conserve and use the energy released in metabolism. Finally, nitrogen is a significant component of nucleic acids such as DNA, the genetic material that allows cells (and eventually whole plants) to grow and reproduce. With the exception of photosynthesis, nitrogen plays the same roles in animals, too. Without nitrogen, there would be no life as we know it.

Adequate nitrogen produces a dark green color in the leaves, caused by the high concentration of chlorophyll. Nitrogen deficiency results in chlorosis (a yellowing) of the leaves because of the declining chlorophyll. This yellowing starts first on oldest leaves, then develops on younger ones as the deficiency becomes more severe. Slow growth and stunted plants are also indicators of nitrogen deficiency. Small grains and other grass-type plants tiller less when nitrogen is in short supply.

Dig even deeper into Nitrogen

Source: Soil Fertility Manual (2006) by the International Plant Nutrition Institute (IPNI) and the Foundation for Agronomic Research (FAR).

Deficiency Symptoms

Symptoms of deficiency can vary across crop species, but similarities exist for how nutrient insufficiency impacts plant tissue color and appearance. Nutrient deficiencies are commonly associated with the physical location on the plant (i.e., whether the symptoms are primarily observed on older versus newly formed plant tissue), but these symptoms can spread as the severity of the deficiency progresses.

All photos are provided courtesy of the International Plant Nutrition Institute (IPNI) and its IPNI Crop Nutrient Deficiency Image Collection. The photos above are a sample of a greater collection, which provides a comprehensive sampling of hundreds of classic cases of crop deficiency from research plots and farm fields located around the world. For access to the full collection, you can visit IPNI's website.