Nitrogen deficiency in wheat: symptoms, look-alikes and fixes

What nitrogen deficiency looks like

DPIRD (WA) calls nitrogen deficiency the most common nutrient deficiency in wheat. Look for these signs:

• Light green to yellow plants across the paddock, often worst on sandy soil or on unburnt header or swathe rows.
• Pale plants with less bulk and fewer tillers.
• The oldest leaf goes first. It yellows from the tip and fades into light green further down.
• Other leaves then yellow, and the oldest leaves turn from yellow to almost white. They may stay alive for some time.
• Stems can be pale pink.
• Plants develop more slowly, but maturity is not greatly delayed. Yield and grain protein both drop.

Old leaves show it first because the plant moves nitrogen out of them to feed new growth (Soil Quality). A handy field clue from DPIRD: double-sown strips look better if nitrogen went out at seeding.

What else could it be

Where and when it shows up

• Cold, wet conditions, which slow the release of nitrogen from organic matter (mineralisation) and slow uptake (DPIRD).
• Soils with very low organic matter.
• High rainfall on free-draining soils, or sandplain soils with traffic pans, where nitrate washes below the roots (leaching).
• Yara adds drought, low or high pH soils, heavy irrigation, and paddocks with lots of undecomposed straw or manure.

How to confirm it

• Plant tissue test: DPIRD recommends a whole-top (whole shoot) test, comparing paired samples from good and poor areas.
• The critical level falls as the crop ages: about 5% N at tillering, down to about 1.5% at boot. Tell the lab the growth stage.
• Ask for sulphur in the same test, since the two look alike.
• A soil nitrogen test on its own is of limited value in most WA soils unless read alongside rotation, soil type and rainfall (DPIRD).
• For budgeting, Soil Quality (NSW) says to take six to seven cores and sample to at least 90 cm, or to the depth of wet soil. See reading a soil test.

In-season fixes

DPIRD lists two options: nitrogen fertiliser or a foliar spray. How much to apply is a budgeting question; use the nitrogen budget worked example and how much urea per hectare for wheat rather than guessing.

• Granular urea topdressed: examples are Granular Urea, Summit Urea and Impact Urea.
• Liquid nitrogen, such as Easy N or UAN. Compare a granular and a liquid option side by side, and read urea vs UAN.
• If sulphur is also short, an ammonium sulphate product such as Gran-Am supplies both (20.2% N, 24% S, per Incitec Pivot). See urea vs ammonium sulphate.

Timing matters. Soil Quality (NSW) notes that tiller numbers and grains per head are set early, so a good supply at establishment is critical. Applying once roots are established, around 3–4 weeks after germination, can improve efficiency. Later applications (first node visible) can still lift yield and let you judge yield potential first, but the later you go, the lower the chance of an economic response.

Watch losses. DPIRD warns urea, and ammonium sources on alkaline soils, can lose nitrogen to the air when topdressed onto dry soil in dewy conditions, though losses rarely exceed 3% a day. Read how much N urea loses before you spread.

After harvest, check grain protein. Soil Quality says crops that keep coming in below the optimum protein for the variety are likely missing yield. Always check with your agronomist before acting.