Nitrogen Deficiency In Crops: How To Detect & Fix It

Why Nitrogen Is So Important For Crops Development

N is critical for vegetation: it is necessary for chlorophyll formation, which is vital for photosynthesis – basically the way for plants to get food. Besides, N is needed for the very plant development: it is a “building block” for amino acids, DNA, membrane proteins, enzymes, most coenzymes, auxins, cytokinins, and merely cells.

This is why it is important to prevent and manage nitrogen deficiency, slowing growth and reducing yields. On the contrary, nitrogen fixation and correct N supply ensure proper growth and full crop production capacity. Another essential drawback of N starvation is low protein levels in grains, e.g., corn and wheat.

What Causes Nitrogen Deficiency In Plants And Affects N Content In Soils?

Certain circumstances may provoke N drops. Being aware of them helps farmers keep the situation under control. The most typical nitrogen deficiency causes are as follows:

• N lack relates to the soil type and is typical for sandy and well-drained soils with fast nutrient leaching.
• Excessive irrigation and heavy rains cause nitrogen deficiency due to overwatering.
• A lack of soil moisture tampers with the absorption of water-soluble nutrients by plant roots.
• Proper soil aeration provides enough O2 to aerobic and facultative aerobic N- fixing bacteria that supply organic N to plants and prevent N starvation. If air content in soils is low, denitrifying bacteria will use NO2 or NO3 instead. Besides, poor aeration causes the split of plant-useful nitrates to N2O, which is a greenhouse gas.
• Soil temperature affects nutrient dissolution and microbial activity to release plant-ingestible N. Thus, the cooler the soil, the less nutrition crops can get.
• High levels of Zn, Mn, K, chlorides are also among the causes of nitrogen deficiency in plants.
• Soil salinity negatively impacts nutrient absorption due to osmotic pressure and decreases N access.
• Soil acidity also affects N availability for crops: either high or low pH is unfavorable.
• Weed infestation provokes N starvation since weeds deprive crops of vital elements.
• Root health is critical for N uptake: when damaged by pests or illnesses, roots absorb nutrients poorly.
• High N solubility is also among the causes of nitrogen deficiency as N is easily washed away from the soil.
• Low organic matter means low plant-available N rates too since organic matter is a natural source of N to crops.

Signs & Symptoms Of Nitrogen Deficiency In Plants

Nitrogen deficiency in a plant can be recognized visually by specific color or shape changes in leaves and stem, forced early flowering, signs of necrosis, etc.

How Quickly Will Plants Show Nitrogen Deficiency?

An N lack can be suspected pretty early since it can be visually noticed on leaves. The pale-green color and yellowing are among nitrogen deficiency symptoms in plants, alongside other nutrient deficiencies. Once noticed, the issue should be immediately addressed; otherwise, slight visual stages of nitrogen deficiency will inevitably get severe.

What Are The Symptoms Of Nitrogen Deficiency In Plants?

A lack of N means a lack of chlorophyll content in plants, and chlorophyll gives vegetation its vibrant green color. This is why nitrogen deficiency at early stages reveals in lighter greens. Then, a nitrogen deficiency causes green leaves to turn yellow, starting from older ones that fade prematurely. Further, the crop nutritional disorder leads to more serious symptoms like necrosis or wilt if not defeated timely.

Farmers can also notice the signs of nitrogen deficiency in early flowering. Stems acquire purple hues, and shoots establish slowly; vegetation is thin and weak.

The last stage of nitrogen deficiency in plants kills them and leads to a complete crop loss.

Root Growth Under Nitrogen Deficiency

Insufficient N content also changes root development: roots grow faster than shoots. Intensive root growth is the so-called forage response to N starvation ^{Zhongtao Jia, Ricardo F.H. Giehl, Nicolaus von Wirén. (2020, July). The Root Foraging Response under Low Nitrogen Depends on DWARF1-Mediated Brassinosteroid Biosynthesis. Plant Physiology, 183(3): 998–1010, https://doi.org/10.1104/pp.20.00440.}: plants explore more areas for the vital nutrient. On the contrary, under abundant N availability, plants reduce root growth to minimize toxicity.

How N Deficiency Develops

Effects of nitrogen deficiency in plants differ depending on the crop nutritional disorder development.

Early signs of nitrogen deficiency start with slight discoloration in maturer leaves: they are lighter than usual. The entire plant looks pale and thin due to insufficient branching. Then, slight nitrogen deficiency changes with more severe symptoms:

1. Larger leaves turn from pale-green to yellow and white.
2. Leaf stems and smaller leaves get reddish or purplish.
3. Veins and petioles become reddish.
4. Stems acquire vertical purplish stripes.
5. Vegetation bursts into forced flowering.
6. Chlorosis spreads from lower parts to the plant’s top.
7. Leaves curl and shed.
8. A nitrogen deficiency shows up as necrotic tissues in crops.
9. Yield volumes considerably decrease.
10. Plants fade prematurely and die.

Under severe nitrogen deficiency – without water, nutrition, cell-building materials, poor photosynthesis and no energy as a result – crops will eventually die.

Specific Examples Of Nitrogen Deficiency Symptoms In Crops

Despite some general signs of nitrogen deficiency in plants, different crops have different visual N starvation manifestations, suffering from different symptoms.

Nitrogen Deficiency In Corn

Since corn seedlings don’t need much N at the beginning, corn nitrogen deficiency symptoms are typically not detected in the early season. Later on, they become visible through pale green or yellowish leaves and thin stems.

The specific nitrogen deficiency symptoms in corn are:

• V-patterned yellowing ^{Adotey, McClure, Raper and Florence. (2021). Visual Symptoms: A Handy Tool in Identifying Nutrient Deficiency in Corn, Cotton and Soybean. University of Tennessee, Institute of Agriculture.} – starting at the leaf tips, spreading along the midrib to the leaf base, and eventually turning brown;
• small ears poorly filled or pinched at the top;
• glossy kernels (due to a lack of proteins and excessive fats);
• brownish stover (at the late season).

Nitrogen Deficiency In Rice

A lack of N impairs rice crop development, manifested in shorter, pale-green stems and short heads. Nitrogen deficiency in rice leaves is identified through:

• light-green and yellowish color in lower young leaves;
• yellowing of leaf tips in older leaves;
• poor canopy production and tillering.

Nitrogen Deficiency In Soybeans

Legumes are known as N-fixation plants that provide N to other crops, yet leguminous soybeans may also suffer from N starvation. An insufficient N content in soybeans results in light-green vegetation and light-yellow foliage with green prominent veins (interveinal chlorosis), which leads to necrosis at the last stage of nitrogen deficiency in plants. Soybean leaves turn pale yellow, with a progression to brown.

Nitrogen Deficiency Symptoms In Cotton

Poor N supply makes cotton foliage light-green, with premature drying and shedding of older leaves. The entire plant is weak, and its overall growth is stunted.

The specific symptoms of nitrogen deficiency in cotton crops include:

• impaired establishment of fruiting branches;
• poor boll formation and retention;
• square and boll abscission ^{Causes of Square and Boll Shedding in Cotton. Technical Bulletin Number 1672. United States Department of Agriculture.} (shedding);
• small boll size;
• red leaf blades in severe cases.

Nitrogen Deficiency Symptoms In Wheat

N starvation impacts the entire wheat growing and development visually manifested by yellowish or light-green foliage. Like in rice crops, nitrogen deficiency in wheat also reduces the number of tillers and stunts the overall growth.

Specific wheat nitrogen deficiency symptoms are as follows:

• discoloration starts in older leaf tips, changing from yellow to light-green that gradually turns white;
• stems may obtain light-pink hues.

However, pale hues don’t necessarily mean nitrogen deficiency in plant leaves – in wheat, it may be due to a lack of K or Mo deficiencies or waterlogging ^{Diagnosing nitrogen deficiency in wheat. (2017, February 27). Department of Primary Industries and Regional Development, Agriculture and Food division.}. For this reason, it is important to mind not only disorder similarities but differences as well, alongside tissue testing and proper situation analysis.

Nitrogen Deficiency Vs. Toxicity

Even though the effects are different, the results of both nutrition disorders are basically the same – impaired growth and reduced yields. Thus, either nitrogen deficiency or toxicity is harmful to crops. Both phenomena relate to N availability to plants. The difference between nitrogen deficiency and toxicity is that under deficiency, crops suffer from an N lack, and in the case of toxicity – from an N excess.

Correspondingly, agronomists should treat nitrogen deficiency and toxicity differently. It is necessary to add the nutrient to plants with an N lack, provided the soil pH rate is correct. With an N excess, it is possible to wash it away with weaker fertilizer solutions.

How To Fix Nitrogen Deficiency In Plants

When crops lack N, the nutrient can be supplied with organic or chemical methods. Prevention of nitrogen deficiency in crops tackles the issue beforehand.

Organic Methods Of Nitrogen Deficiency Treatment

Organic matter not only adds vital nutrients for plants but improves soil structure and helps retain soil moisture. Basic sources of N supply are widely used in organic farming and include:

• compost;
• animal manure;
• N-fixing plants (e.g., legumes);
• horn, bone, fish, or blood meal;
• nettle slag;
• groundnut husks;
• coco peat (coir pith);
• edible and non-edible oil cakes;
• green manure;
• tree leaves;
• ashes, etc.

There are many manures that can be a solution to nitrogen deficiency. N concentration in different manures varies ^{Krishan Chandra. (2005, January). Organic manures. Regional Centre of Organic Farming.}. In particular, blood meal, groundnut husks and cake, coco peat are much richer in nitrogen compared to coal or wood ash and fresh poultry or green cowpea manure. Cover crops, crop rotation as well as intercropping help prevent nitrogen deficiency by growing legumes.

Chemical Methods To Fix Nitrogen Deficiency

Inorganic amendments suggest using synthesized N-containing fertilizers to promote crop recovery from nitrogen deficiency, e.g., NPK, nitrolime, ammonium nitrate, urea, etc. Soil testing before a cropping season will help understand the required corrections of pH and nutrient content.

Most chemical fertilizers have a balanced formula with an indicated NPK ratio. The first number stands for N content. The higher the nutrient needs, the higher is the required amount.

Preventative Measures In Nitrogen Deficiency Management

Prevention helps to avoid the issue of N starvation. The following measures will spare farmers the trouble of fixing severe nitrogen deficiency by addressing the issue in advance:

• proper soil drainage;
• balanced use of fertilizers;
• organic matter applications;
• soil testing before seeding;
• plant tissue analysis for N starvation.

Apart from that, certain agricultural practices enrich the soil with nitrogen, and here is why:

• Regular sufficient (but not excessive) irrigation prevents both plant burns and N leakage.
• Fertilization and fertigation increase N concentration in soils. In particular, drip fertigation supplies nutrients directly to the plant’s root zone.

When fixing nitrogen deficiency, it’s important to maintain a proper balance. Each crop has specific needs. When a balance is shifted to any side, it always affects yields adversely. In particular, N saturation can significantly complicate the sweet potatoes growing and reduce yields. The surprising phenomenon can be explained by the fact that N boosts the shoot growth while sweet potatoes are grown for roots.

How To Deal With Nitrogen Deficiency With EOSDA Crop Monitoring

Inspecting fields for visual signs of nitrogen deficiency by far is not the only way. Remote sensing and satellite-based analytics help monitor the crop state to notice the problem on time.

Weather Monitoring

Weather conditions influence the nitrogen balance that crops need for healthy development. Either droughts or downpours adversely affect the nitrogen balance. EOSDA Crop Monitoring allows the farmers to be aware of weather anomalies by providing 14-day forecasts. With such data, the software facilitates the field activities planning to maintain the required level of nutrients for healthy crop growth, including but not limited to N. This will help eliminate nitrogen deficiency in plants.

Waterlogging Identification

Flooding or field waterlogging can occur not only due to heavy rains or relief specifics but also due to over-irrigation. The NDMI index shows the moisture content in crops, which helps estimate how wet the field is. With no recent rains but high NDMI values, there is a high probability of excessive irrigation events.

EOSDA Crop Monitoring also assists in carrying out all agricultural activities on each field or its separate zones. The Field activity log on the software is an excellent planner as well. Thus, if each activity is recorded in the system, the farmer will always know what has been done in the field and where exactly. It allows excluding the human factor of mistakenly repeated irrigation, fertigation, or any other agricultural activity, saving resources, and maintaining crop health.

Monitoring Crops Health At Active Stages Of Their Development

Despite yellowing and stunting, occurring due to various factors, N still directly impacts chlorophyll rates. This is why its reduced availability causes certain changes in crops. As crops highly need N at the active stages of plant growth, one can notice the signs through ReCl index values. This vegetation index is particularly useful in EOSDA Crop Monitoring during their active growth: low index values indicate deviations in vegetation development, possibly, because of nitrogen deficiency in plants.

Balance Is The Key

Nitrogen deficiency negatively affects crops, but too much nitrogen also reduces productivity. If nitrogen is low, crops suffer from chlorosis, starting in older foliage because plants reallocate N from mature to newer leaves. N starvation hinders the overall growth and decreases the establishment of fruits.

With excessive nitrogen, fruits ripen slowly, are too soft, and spoil faster. High nitrogen content is particularly undesirable for root crops since N forces shoots grow quicker than roots. Extra nitrogen makes crops ultimately sensitive to water or cold stresses and pathogen attacks.

This is why it is necessary to maintain the proper balance, to avoid both nitrogen deficiency and toxicity. EOSDA Crop Monitoring always stays alert to notice any development deviances on time, enabling farmers to address the problem early and avoid crop losses due to nitrogen deficiency issues.