Nitrogen deficiency in plants: symptoms, causes and how to correct it

Photo at the top: A French bean plant short of nitrogen: the whole plant is pale yellow-green, while the healthy plants beside it stay dark green, Photo: Rasbak, CC BY-SA 3.0

Quick answer

Nitrogen deficiency in plants means the crop does not get enough nitrogen (N), the nutrient it needs most for growth. Older, lower leaves turn pale, then yellow, while the top stays greener. Plants stay short, with fewer tillers or branches and a smaller harvest. Confirm it with a soil test and correct it with manure and split doses of fertiliser.

How to identify nitrogen deficiency in plants

Nitrogen is part of chlorophyll, the green colour that lets a leaf make food from sunlight. It is also part of every protein in the plant. So a plant short of nitrogen loses its green colour and grows slowly.

Nitrogen moves inside the plant. When there is not enough, the plant pulls it out of the old leaves and sends it to the new ones. That is why the symptoms always start on the lower, older leaves.

Nitrogen deficiency symptoms in leaves and plants

• Colour: the whole plant looks pale green. The older leaves turn yellow first, often from the tip. In a bad case they dry and die.
• Growth: plants are short and thin, with small leaves. Cereals make fewer tillers. Cotton and vegetables make fewer branches.
• Crop: fewer flowers, smaller ears, cobs, bolls and fruits, and the crop may mature early with a lower harvest.
• In the field: pale patches often follow the pattern of the problem: sandy spots, waterlogged corners, or strips where fertiliser was missed.

Look-alikes and how to tell them apart

Many problems make a crop yellow. Look at which leaves turn yellow first, and how.

• Sulphur deficiency: also an even, pale yellow, but it starts on the young, top leaves, because sulphur does not move easily inside the plant.
• Iron deficiency: young leaves turn yellow between the veins, while the veins stay green.
• Magnesium deficiency: older leaves turn yellow between the veins, while the veins stay green. With nitrogen deficiency the whole old leaf turns yellow, veins too.
• Potassium deficiency: older leaves get brown, scorched edges and tips, while the middle of the leaf stays green for a while.
• Zinc deficiency in paddy (khaira): rusty brown spots on the leaves and stunted, bushy plants, usually a few weeks after transplanting. See our guide to khaira disease in rice and zinc deficiency in crops.
• Root problems: waterlogging, root pests, nematodes or root rot can stop roots from taking up nitrogen even when there is enough in the soil. Pull out a few plants and check the roots.
• Virus: yellowing in a mosaic pattern, curling or yellow veins on young leaves points to a virus, not a nutrient problem.
• Normal ageing: near harvest, lower leaves naturally turn yellow as the plant moves nitrogen into the grain.

Causes of nitrogen deficiency in plants

Most of the nitrogen a crop uses comes from the soil and from fertiliser. A shortage usually has one of these causes:

• Low soil nitrogen: many Indian soils are low in available nitrogen, especially light, sandy and red soils with little organic matter.
• Too little fertiliser, or at the wrong time: a crop needs most nitrogen during fast growth (tillering in paddy, knee-high to tasseling in maize, squaring and flowering in cotton). If the dose was small or came too early, the crop runs short later.
• Losses after heavy rain: nitrogen in the nitrate form washes down below the roots in sandy soils after heavy rain or too much irrigation. Watch for pale crops on light red soils after heavy kharif rains.
• Waterlogging: in soils that stay wet without air, soil bacteria turn nitrate into gas, which escapes into the air. Roots also work poorly without air.
• Urea left on the surface: urea spread on dry, hot ground and not mixed in or watered in can lose part of its nitrogen into the air as ammonia.
• Fresh crop waste: when a lot of fresh straw or stubble is ploughed in, soil microbes use soil nitrogen to break it down. The next crop can look pale for a few weeks.
• Cold or very dry soil: roots take up less, and organic matter releases nitrogen slowly.

Nitrogen deficiency symptoms by crop

Paddy (rice)

Plants are short and pale yellow-green, with fewer tillers. Older leaves turn yellow from the tip. TNAU Agritech also notes that leaves become narrow, short and upright. Panicles are small with fewer grains. The most sensitive times are tillering and panicle initiation.

Maize

Yellowing starts at the tip of the lower leaves and runs down the middle of the leaf in a V shape. The leaf then dries from the tip. Plants are thin and short, and cobs are small, with unfilled tips.

Cotton

Plants are small and pale green. Older leaves turn yellow, sometimes reddish, and drop early. The plant makes fewer squares (flower buds) and bolls, and bolls stay small.

Chilli

Lower leaves turn pale and yellow, plants stay thin with few branches, and flower and fruit numbers drop.

Tomato

Older leaves turn evenly yellow and fall. Stems become thin and hard and may turn purplish. Flowers and fruit set drop, and fruits stay small.

When to act: soil test and field checks

There is no "threshold" to wait for. A crop short of nitrogen loses yield every day. But confirm the cause before you add more fertiliser, because the look-alikes above need a different fix.

• Soil test before sowing: under the Soil Health Card scheme you can get your soil tested through your agriculture department or Krishi Vigyan Kendra (KVK). The report gives nitrogen, phosphorus, potassium and other nutrients, with a fertiliser plan for your crop.
• How to take a soil sample: from 8–10 spots across the field, in a zigzag, dig a V-shaped pit to plough depth (about 15 cm) and take a thin slice from one side. Mix all slices in a clean bucket and send about half a kilogram. Do not sample near bunds, trees, manure heaps or fertiliser bands.
• Leaf colour chart for paddy: a simple plastic chart with shades of green. You hold the youngest fully opened leaf against it. Ask your local agriculture officer or KVK for the chart and the reading at which to apply nitrogen for your variety.
• Check the field pattern: if only low, wet patches are pale, fix the drainage first. If only one strip is pale, fertiliser may have been missed there.

Correcting it without chemical fertiliser

Organic sources release nitrogen slowly and also build up the soil. They are good for long-term soil health, and they work with fertiliser, not instead of it, when a crop is already short.

• Farmyard manure (FYM) and compost: apply well-rotted manure before sowing or transplanting and mix it into the soil. Fresh, raw manure can tie up nitrogen for a while.
• Vermicompost: richer and quicker-acting than ordinary compost. Useful in vegetables and nurseries.
• Green manure: grow dhaincha or sunhemp before paddy, and plough it in before transplanting, as advised by your local agriculture office.
• Legumes in rotation: pulses such as green gram, black gram and red gram add nitrogen to the soil through their root nodules. Rotate cereals and cotton with them.
• Biofertilisers: Azospirillum and Azotobacter for cereals and vegetables, Rhizobium for pulses, and Azolla in paddy fields. Use registered products and follow the label.
• Crop residue: do not burn straw. Let it rot in the field or compost it, and give a little extra nitrogen to the next crop when fresh residue is ploughed in.

How to fix nitrogen deficiency in plants with fertiliser

Soil application

Soil application is the main way to correct nitrogen. Plants need far more nitrogen than a leaf spray can supply. Follow the dose in your soil test report or your state's crop recommendation.

• Split the dose: give nitrogen in two or three parts: at sowing or transplanting, and at the main growth stages (tillering and panicle initiation in paddy, knee-high stage in maize, squaring and flowering in cotton). Split doses waste less and match the crop's need.
• Apply to moist soil: put urea into moist soil, or water it in soon after spreading, and mix it in where you can. Do not spread it on hot, dry ground and leave it.
• In paddy: apply urea in a thin film of water or on saturated soil, and do not let water run out of the field for a few days after.
• Neem-coated urea: urea sold in India is neem-coated. The coating slows the release a little, so less is lost.
• Fix drainage first if the problem comes from waterlogging. Fertiliser on a waterlogged field is largely wasted.

Foliar spray

Foliar spray is only a quick top-up. A dilute spray of a water-soluble nitrogen fertiliser can green up a pale crop within a few days, for example after a spell of heavy rain. It does not replace soil application. Use only the strength your local agriculture officer or the product label gives: too strong a spray burns leaves. Spray in the early morning or evening, not in hot sun.

Too much nitrogen is also a problem

Do not overcorrect. Excess nitrogen makes a soft, dark green crop that draws pests and diseases and can fall over (lodge).

• In paddy, heavy nitrogen favours brown plant hopper in paddy, sheath blight of rice and rice blast (leaf and neck blast).
• In cotton and vegetables, a lush crop draws sucking pests such as whitefly and aphids.
• Too much nitrogen late in the season delays maturity and can lower grain and fruit quality.

Safety

• Store fertiliser in a dry place, away from food, animal feed, children and pesticides.
• Wear gloves while handling fertiliser, and wash your hands afterwards.
• Do not place urea in direct contact with seed. It can harm germination.
• Do not let fertiliser wash into ponds, canals or wells.
• Read the label and leaflet before use.

Frequently asked questions

What are the symptoms of nitrogen deficiency in plants?

The plant turns pale green. The older, lower leaves turn yellow first, often from the tip, while the top stays greener. Plants are short and thin, with fewer tillers or branches and a smaller harvest.

Why do the lower leaves turn yellow first?

Nitrogen moves inside the plant. When the plant runs short, it takes nitrogen from the old leaves and sends it to the new growth. So the old leaves lose their colour first.

Is every yellow leaf a sign of nitrogen deficiency?

No. If the young leaves turn yellow first, or the veins stay green, or there are spots or curling, the cause is likely something else, such as sulphur, iron, magnesium or zinc deficiency, waterlogging or a virus. A soil test and a look at the roots help you decide.

Which fertiliser gives nitrogen to plants?

Urea is the most common nitrogen fertiliser in India. Ammonium sulphate, calcium ammonium nitrate and DAP also supply nitrogen, and DAP gives phosphorus too. Manure, compost and green manure add nitrogen slowly. Your soil test report tells you which to use and how much.

How fast does a crop recover after I add nitrogen?

If the soil is moist and the roots are healthy, new leaves usually green up within one to two weeks after soil application. Old leaves that are fully yellow will not turn green again. A foliar spray shows a colour change faster, but it is only a short top-up.

Related reading

• Khaira disease in rice and zinc deficiency in crops: signs and correction
• Boron deficiency in plants: symptoms in cotton, groundnut, tomato, chilli and brinjal
• Brown plant hopper in paddy: symptoms, treatment and control
• All fertilizers
• Products for paddy
• Products for cotton

Sources

• TNAU Agritech Portal, Tamil Nadu Agricultural University: Rice: nitrogen deficiency
• Soil Health Card scheme, Department of Agriculture and Farmers Welfare, Government of India: soilhealth.dac.gov.in