What's the Function of Nitrogen (N) in Plants?
•Posted on November 02 2016
Last updated: February 18, 2026
Technical Review by: Amir Tajer, B.S.M.E., QAL — Co-Owner & Technical Director, Greenway Biotech
Reviewed against: University of Missouri Extension, Kansas State Extension, Penn State Plant Science, and Michigan State University Extension guidelines
Disclosure: Greenway Biotech manufactures nitrogen fertilizers mentioned in this guide. Alternative formulations and organic options are also discussed.
⚡ Quick Facts: Nitrogen in Plants
- What it does: Nitrogen is a core building block of amino acids, proteins, chlorophyll, and DNA in plants
- Atmosphere share: ~78% of Earth's atmosphere is nitrogen gas, but plants cannot use it directly
- Plant uptake forms: Nitrate (NO₃⁻) and ammonium (NH₄⁺) are the two forms roots absorb
- Deficiency signs: Yellowing of older (lower) leaves first, stunted growth, reduced flowering and fruit set
- Most commonly limiting: Nitrogen is among the most commonly limiting nutrients in managed soils and gardens worldwide
- Quick correction: Water-soluble nitrogen fertilizers like Ammonium Sulfate 21-0-0 or Calcium Nitrate 15.5-0-0 deliver fast results
- Organic option: Blood Meal 13-0-0 provides a slow-release, organic nitrogen source
Nitrogen is the nutrient that makes or breaks your garden. It's the engine behind lush green leaves, strong stems, and abundant harvests — yet it's also the nutrient most likely to be deficient in your soil. Understanding how nitrogen functions in plants, recognizing when your crops need more (or less) of it, and knowing which fertilizer to reach for can mean the difference between a thriving garden and a struggling one.
Despite making up roughly 78% of Earth's atmosphere, nitrogen gas (N₂) is locked in a form that plants simply cannot use[1]. Plants depend on soil-based forms — primarily nitrate and ammonium — to meet their nitrogen needs. This guide walks you through everything you need to know about nitrogen in plants: what it does, how to spot deficiency, which fertilizer forms work best, and how to apply them correctly for both soil and hydroponic growing.
Why Is Nitrogen Important to Plants?
Nitrogen is a paramount element for plant survival because it's embedded in nearly every major biological molecule a plant produces. From the chlorophyll that captures sunlight to the DNA that carries genetic instructions, nitrogen is involved at every level of plant biology[2].
Plants need both macronutrients and micronutrients to stay healthy — nitrogen, phosphorus, and potassium are the "big three" macronutrients, often listed as NPK on fertilizer labels. Of these, nitrogen is typically required in the largest quantities and is most often the limiting factor in plant growth[1].
Think of nitrogen as the fuel that powers a plant's growth engine. Without adequate nitrogen, a plant cannot manufacture the proteins needed for new cell growth, the chlorophyll needed for photosynthesis, or the nucleic acids needed for reproduction. Even if every other nutrient is abundant, a lack of nitrogen stalls the entire system.
🔬 Did You Know?
Nitrogen ranks as the fourth most abundant element in plant dry weight — behind only carbon, hydrogen, and oxygen[4]. Unlike those three elements (which plants obtain from air and water), nitrogen must be absorbed from the soil through the roots.
The wellness of every plant part — leaves, roots, stems, flowers, and fruit — depends on having enough nitrogen available throughout the growing season. When soil nitrogen drops below what plants need, the effects are visible quickly and can severely reduce both yield and quality.
What Does Nitrogen Do for Plants?
Nitrogen could fairly be called the backbone of plant biology. It plays essential roles in structure, energy, genetics, and metabolism. Here's a closer look at the key functions:
Protein and amino acid synthesis. Nitrogen is a core element in every amino acid, which are the building blocks of all plant proteins. These proteins serve as structural components in cell membranes and as enzymes that catalyze virtually every biochemical reaction in the plant[1]. Without nitrogen, plants cannot build new cells, which means growth halts entirely.
Chlorophyll production. Chlorophyll — the green pigment responsible for capturing light energy during photosynthesis — contains nitrogen at its molecular core. Plants with sufficient nitrogen typically exhibit deep green color and vigorous photosynthetic activity. When nitrogen drops, chlorophyll production declines, and leaves begin to yellow[2].
DNA and genetic material. Nitrogen is a component of nucleic acids (DNA and RNA), which carry the genetic code that controls plant traits, reproduction, and cellular function[4]. Every time a plant cell divides, it needs nitrogen to replicate its genetic material.
Energy transfer. Adenosine triphosphate (ATP) — the primary energy currency in plant cells — contains nitrogen. ATP powers active nutrient transport, cell signaling, and the synthesis of complex molecules[5].
Stress resistance. Adequate nitrogen levels help plants cope with environmental stresses including drought, temperature extremes, and pest pressure. Nitrogen contributes to the synthesis of stress-related proteins and metabolites that improve resilience[4].
🔬 Did You Know?
Nitrogen is "mobile" within the plant, meaning it can be redistributed from older tissues to newer, more actively growing parts[3][6]. This is why deficiency symptoms appear on older, lower leaves first — the plant salvages nitrogen from expendable tissue and sends it where it's needed most.
Nitrogen Deficiency in Plants: Symptoms and Causes
Even though nitrogen is abundant in the atmosphere, it can easily become deficient in soil — and when it does, the effects on plants are dramatic.
Common Symptoms of Nitrogen Deficiency
Nitrogen deficiency generally progresses through recognizable stages. Early on, the entire plant may appear slightly pale or lighter green than normal[6]. As the deficiency worsens, symptoms become more pronounced:
Older (lower) leaves turn yellow first, progressing from leaf tips inward toward the stem. This pattern occurs because nitrogen is mobile — the plant redirects it from older leaves to support new growth. Growth slows noticeably, and the plant may appear thin and stunted. Flowering, fruit set, and overall yield decline significantly. In severe cases, yellowed leaves develop brown, necrotic tissue and eventually drop off the plant[7].
⚠️ Important: Don't Assume Yellowing Means Nitrogen
Yellowing leaves can also result from deficiencies in potassium, sulfur, iron, magnesium, or zinc — as well as herbicide injury or root damage[8]. The most reliable way to confirm nitrogen deficiency is a soil test combined with visual symptom assessment. A basic soil test typically costs $15–30 and can prevent costly misdiagnosis.
Common Causes of Nitrogen Deficiency
Several factors can deplete soil nitrogen or make it unavailable to plants. Heavy rainfall leaches nitrate from the root zone, which is especially problematic in sandy soils with low organic matter. Adding high-carbon materials (like fresh sawdust or wood chips) to soil can temporarily "lock up" nitrogen, because soil microorganisms consume available nitrogen to decompose the carbon-rich material[10]. Continuous cropping without replenishment gradually depletes soil nitrogen reserves. Cold, wet soil slows microbial activity that converts organic nitrogen into plant-available forms. Soil pH that is too high or too low can reduce nitrogen availability even when total soil nitrogen is adequate.
Related: What Is Ammonium Sulfate Used For?
How to Fix Nitrogen Deficiency in Plants
Correcting nitrogen deficiency involves both immediate treatment and longer-term soil building strategies. The approach you choose often depends on how severe the deficiency is and whether you prefer organic or conventional methods.
Fast-Acting (Water-Soluble) Nitrogen Sources
When plants are visibly deficient and need correction within days, water-soluble nitrogen fertilizers are generally the most effective option. These dissolve completely in water and deliver nitrogen directly to the root zone:
Ammonium Sulfate 21-0-0 — Provides both nitrogen (21%) and sulfur (24%). Works well in alkaline soils and helps lower soil pH gradually.
Mix: 12 grams (approximately 1 tablespoon) per gallon of water
Apply: 1 cup (8 fl oz) of solution per plant for containers; 1 gallon per 50 sq ft for beds
Dose received: Approximately 0.16 g actual nitrogen per cup of solution (12 g ÷ 16 cups × 21% N)
Coverage: One gallon of mixed solution treats about 16 container plants, delivering ~2.5 g total nitrogen
Calcium Nitrate 15.5-0-0 — Delivers nitrogen in nitrate form (immediately available) plus 19% calcium. Often preferred for fruiting crops where calcium prevents blossom end rot.
Urea 46-0-0 — The most concentrated nitrogen fertilizer available. Best for large-area applications and situations where maximum nitrogen per dollar matters.
Slow-Release and Organic Nitrogen Sources
For longer-term soil building, organic nitrogen sources release nutrients gradually as soil microorganisms break them down:
Blood Meal 13-0-0 — One of the highest-nitrogen organic fertilizers available. Releases over 4–6 weeks and provides a noticeable greening effect within 1–2 weeks.
Feather Meal 12-0-0 — Slower release than blood meal, providing steady nitrogen over 2–3 months. Works well as a pre-plant amendment.
Crustacean Meal 4-0-0 — Lower nitrogen but adds chitin to soil, which can stimulate beneficial microbial activity and may support natural pest resistance.
💡 Pro Tip: Combine Fast and Slow Sources
For severe deficiencies, many experienced growers apply a water-soluble nitrogen fertilizer for immediate correction while simultaneously working an organic meal into the soil for sustained feeding. This "quick fix plus long-term" approach often delivers the best results.
Before You Choose a Nitrogen Fertilizer
While water-soluble nitrogen works well for most deficiency situations, the best choice depends on your specific soil, crops, and growing conditions. Here's how to decide:
| Your Situation | Best Approach |
|---|---|
| Haven't soil tested yet | Start with a soil test ($15–30); apply a balanced fertilizer at half-rate while waiting for results |
| ⭐ Confirmed nitrogen deficiency via soil test | Apply water-soluble nitrogen (Ammonium Sulfate or Calcium Nitrate) for fast correction |
| Alkaline soil (pH above 7.0) | Ammonium Sulfate 21-0-0 — provides nitrogen while gradually lowering pH |
| Fruiting crops (tomatoes, peppers) | Calcium Nitrate 15.5-0-0 — delivers nitrogen plus calcium to prevent blossom end rot |
| Organic garden / certified organic | Blood Meal 13-0-0 or Feather Meal 12-0-0 |
| Large area on a budget | Urea 46-0-0 — highest nitrogen per dollar; best for broadcast applications |
| Hydroponic systems | Calcium Nitrate for base nitrogen; supplement with Ammonium Sulfate to fine-tune pH |
💡 Soil Testing Saves Money
A $15–30 soil test reveals exactly what your plants need. Testing prevents both deficiencies and expensive over-application. Most university extension offices offer affordable soil testing services — check with your local land-grant university extension for details.
Ammonium vs. Nitrate vs. Urea: Which Nitrogen Form Is Best?
Not all nitrogen is created equal. The three main forms behave differently in soil and inside the plant, and understanding these differences helps you choose the right product for your situation.
| Characteristic | Ammonium (NH₄⁺) | Nitrate (NO₃⁻) | Urea (CO(NH₂)₂) |
|---|---|---|---|
| Availability | Immediate — plant roots absorb NH₄⁺ directly; may also be nitrified to nitrate over time by soil bacteria | Immediate — most readily absorbed form; no conversion needed | Slow — must convert to ammonium first, then may be nitrified to nitrate in soil |
| Soil mobility | Low — binds to soil particles, resists leaching | High — moves freely with water, prone to leaching | Moderate — stays in place until converted |
| pH effect | Acidifying — lowers soil pH over time | Slightly alkalizing or neutral | Initially alkalizing, then acidifying after conversion |
| Best use case | Alkaline soils; crops that prefer slightly acidic conditions | ⭐ Fast correction; hydroponic systems; calcium-demanding crops | Large-area applications where cost per unit of nitrogen matters most |
| Greenway product | Ammonium Sulfate 21-0-0 | Calcium Nitrate 15.5-0-0 | Urea 46-0-0 |
For most home gardeners, nitrate-based fertilizers are often the easiest starting point because plants can absorb nitrate immediately without waiting for soil microbes to convert it. Ammonium sources are particularly valuable in alkaline soils or when you want nitrogen to stay put rather than leach away with irrigation or rain. Urea is the most economical option per unit of nitrogen and works well for broadcast applications on lawns and large garden areas.
In practice, many successful growers use a combination. For example, a base application of Calcium Nitrate for quick feeding supplemented with Ammonium Sulfate for sustained availability is a common strategy in both soil and hydroponic systems.
🔬 Did You Know?
In waterlogged or poorly drained soils, microorganisms can convert nitrate back into nitrogen gas through a process called denitrification — essentially sending your applied nitrogen back into the atmosphere[9]. Denitrification becomes significant when soil is waterlogged for 36 hours or more. This is one reason good drainage is critical for efficient nitrogen use.
How Is Nitrogen Used in Hydroponic Gardening?
Nitrogen is just as essential in hydroponic systems as it is in soil gardens — the total requirement is similar, but the delivery method is entirely different[1].
In hydroponics, there's no soil reservoir to buffer nutrient fluctuations. Plants depend entirely on the nutrient solution you provide, which means getting nitrogen concentration and form right is critical. Most hydroponic nutrient programs deliver nitrogen primarily as nitrate (from Calcium Nitrate) with a smaller proportion as ammonium (from Ammonium Sulfate or Magnesium Nitrate 11-0-0).
The nitrate-to-ammonium ratio matters because it directly affects solution pH. Nitrate uptake tends to raise pH in the root zone, while ammonium uptake lowers it. A common practice among hydroponic growers is to target roughly 75–80% nitrate and 20–25% ammonium to help maintain pH stability, though optimal ratios can vary by crop species and system type.
⚠️ Important: Hydroponic Nitrogen Safety
Excessive nitrogen concentration in hydroponic solution can cause rapid, soft growth with weak cell walls, making plants susceptible to disease and mechanical damage. Start with established formulation guidelines and increase gradually based on plant response. Our 4-Part Hydroponic Bundle includes balanced ratios designed for common crop types.
Diagnosing Nitrogen Problems in Your Garden
Most nitrogen-related issues show visible symptoms before they cause irreversible damage. Learning to recognize and respond early can save your harvest. Keep in mind that these symptoms can overlap with other nutrient deficiencies, so a soil test is always the most reliable diagnostic tool.
| Symptom | Likely Cause | Solution |
|---|---|---|
| Yellow older (lower) leaves, progressing upward | Nitrogen deficiency | Apply water-soluble nitrogen fertilizer; confirm with soil test |
| Entire plant pale green, stunted growth | Moderate nitrogen deficiency; possibly compounded by cold soil | Foliar feed with dilute nitrogen solution for quick uptake; address soil temperature if applicable |
| Very dark green leaves, lush foliage but few flowers/fruit | Nitrogen excess | Stop nitrogen applications; increase watering to leach excess; shift to phosphorus/potassium focus |
| Yellowing after adding wood chips or sawdust | Nitrogen immobilization — microbes consuming N to decompose carbon | Apply supplemental nitrogen to compensate; or compost high-carbon materials before adding to beds |
| Yellowing only on youngest leaves (top) | Likely NOT nitrogen — suspect iron, sulfur, or manganese deficiency | Test soil; consider Chelated Iron EDTA or Chelated Manganese EDTA |
| Brown leaf edges with yellowing | Possibly potassium deficiency (often confused with nitrogen) | Test soil; apply Potassium Sulfate 0-0-53 if confirmed |
| Plants wilt despite adequate water | Root damage from excess fertilizer salt buildup | Flush soil with clean water; reduce fertilizer concentration; test soil EC |
💡 Pro Tip: Document Before Treating
Take photos of problem symptoms before applying any treatment. If the issue doesn't improve within 10–14 days, send your soil test results and photos to your local university extension office for expert diagnosis. You can also reach our team at questions@greenwaybiotech.com — we're happy to help identify the issue.
🌱 Shop Our Nitrogen Fertilizer Collection
Whether you need fast-acting water-soluble formulas or slow-release organic options, our nitrogen fertilizer collection has you covered. All products are tested for purity, free from heavy metal contamination, and backed by our satisfaction guarantee.
Shop Nitrogen Fertilizers🎯 Key Takeaways
- Nitrogen is essential for amino acid synthesis, chlorophyll production, DNA replication, and energy transfer in plants
- Despite making up 78% of the atmosphere, plants can only absorb nitrogen in soil-based forms — nitrate (NO₃⁻) and ammonium (NH₄⁺)
- Deficiency symptoms typically start with yellowing of older, lower leaves and progress upward as nitrogen is redirected to new growth
- A soil test is the most reliable way to confirm nitrogen deficiency and avoid misdiagnosis
- Water-soluble fertilizers like Ammonium Sulfate 21-0-0 and Calcium Nitrate 15.5-0-0 provide fast correction
- Organic options like Blood Meal 13-0-0 and Feather Meal 12-0-0 build long-term soil nitrogen
- In hydroponics, a common practice is to target roughly 75–80% nitrate to 20–25% ammonium for pH stability, though ratios vary by crop
❓ Frequently Asked Questions
What does nitrogen do for plants?
Nitrogen serves as a building block for amino acids, proteins, chlorophyll, DNA, and ATP in plants. It drives leaf and stem growth, supports photosynthesis, and enables cell division. Without adequate nitrogen, plants cannot produce new tissue, resulting in stunted growth and yellowing leaves.
How do I know if my plants need more nitrogen?
The most common visual sign is yellowing of older (lower) leaves that progresses upward. Plants may also appear pale green overall, grow slowly, or produce fewer flowers and fruit than expected. However, these symptoms can overlap with other deficiencies, so a soil test is the most reliable way to confirm. Contact your local extension office or use a home soil test kit.
What is the fastest way to add nitrogen to soil?
Water-soluble nitrogen fertilizers deliver the fastest results. Products like Ammonium Sulfate 21-0-0 or Calcium Nitrate 15.5-0-0 dissolve in water and make nitrogen available to roots within hours. Mix 12 grams (about 1 tablespoon) per gallon of water and apply as a soil drench for quick correction.
Can you have too much nitrogen in soil?
Yes. Excess nitrogen often produces very dark green, lush foliage but reduced flowering and fruit production. Plants may grow tall and leggy with weak stems. In severe cases, excess nitrogen can burn roots, make plants susceptible to disease, and contribute to environmental issues like groundwater contamination. This is why soil testing and following recommended application rates is important.
What is the best organic nitrogen fertilizer?
Blood Meal 13-0-0 is one of the highest-nitrogen organic fertilizers available and releases nutrients over 4–6 weeks. Feather Meal 12-0-0 is another strong option that provides nitrogen over a longer 2–3 month period. Both work well for building soil fertility without synthetic inputs.
Is ammonium or nitrate nitrogen better for plants?
Neither is universally better — it depends on your soil and growing situation. Nitrate nitrogen is immediately available and works well in hydroponic systems, but it leaches easily from soil. Ammonium nitrogen resists leaching and is useful for acidifying alkaline soils, but it requires microbial conversion before plants can fully utilize it. Many growers use both forms together for balanced availability.
How often should I apply nitrogen fertilizer?
Application frequency depends on the fertilizer type and your crops. Water-soluble fertilizers typically need reapplication every 2–4 weeks since they're rapidly available but also deplete quickly. Organic meals like blood meal or feather meal generally last 4–12 weeks depending on soil temperature and microbial activity. Always follow label rates and adjust based on plant response and soil test results.
📚 Sources
- Nitrogen — Mosaic Crop Nutrition
- Nitrogen in the Plant — University of Missouri Extension
- Diagnosing Nutrient Deficiencies in the Field (MF3028) — Kansas State University Extension
- The Utilization and Roles of Nitrogen in Plants — Forests (MDPI), 2024
- Nitrogen Journey in Plants: From Uptake to Metabolism, Stress Response, and Microbe Interaction — PMC/NCBI, 2023
- Watch Out for These Nutrient Deficiency Symptoms — UConn Home & Garden Education Center
- Nitrogen Deficiency — Penn State Department of Plant Science
- Are You Sure That Yellowing Means Nitrogen Deficiency? — Michigan State University Extension
- Nitrogen in the Environment: Denitrification — University of Missouri Extension
- Nitrogen in the Environment: Mineralization — Immobilization — University of Missouri Extension
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I want information about fertilisers who increase cold temperature in plants
Kapingapaul: Hi there, thank you so much for your suggestion! We will update this article as soon as we can. Please let us know if we can provide any further assistance.
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