Diagnosing nitrogen deficiency in wheat
Nitrogen deficiency is the most common nutrient deficiency in wheat especially during cold, wet conditions and in well-drained soils in high rainfall areas.
What to look for
- Light green to yellow plants particularly on sandy soils or unburnt header or swathe rows.
- Double sown areas have less symptoms if nitrogen fertiliser was applied at seeding.
- Plants are pale green with reduced bulkand fewer tillers.
- Symptoms first occur on oldest leaf, which becomes paler than the others with marked yellowing starting at the tip and gradually merging into light green.
- Other leaves start to yellow and oldest leaves change from yellow to almost white.
- Leaves may not die for some time.
- Stems may be pale pink.
- Nitrogen deficient plants develop more slowly than healthy plants, but maturity is not greatly delayed.
- Reduced grain yield and protein levels.
What else could it be
|Diagnosing waterlogging in cereals||Pale plants with oldest leaves most affected||Root browning or lack of feeder roots and wet soil|
|Diagnosing potassium deficiency in wheat||Pale plants with oldest leaves most affected||Differences include more marked leaf tip death and contrast between yellow and green sections of potassium deficient plants. Tillering is less affected.|
|Diagnosing molybdenum deficiency in cereals||Pale poorly tillered plants||Molybdenum deficiency affects the middle leaves first and cause white heads, shrivelled grain and delayed maturity|
Where does it occur?
- Nitrogen deficiency can occur on most WA soils but is most common in the following situations.
- In cold, wet conditions that slow nitrogen mineralisation and the uptake of nitrogen.
- Soils with very low organic matter.
- High rainfall on well-drained soils and soils with sandplain traffic pans can result in nitrogen leaching.
- Nitrogen fertiliser or foliar spray.
- There is a risk of volatilisation loss from urea or (ammonium sources of nitrogen on alkaline soils) when topdressesd on dry soils in dewy conditions. Losses rarely exceed 3% per day
How can it be monitored?
- Use whole-top plant test to diagnose suspected nitrogen deficiency and compare paired good/poor plant samples where possible. Critical N concentration decreases as the plant ages/matures. Critical N value for whole shoots is about 5% at tillering decreasing to 1.5% at the boot stage.
- Nitrogen soil testing is of limited value for most soils unless used in conjunction with other rotational, soil type and rainfall information.
- Tools such as the Select Your Nitrogen calculator that combines 0 -10 centimetres soil test organic carbon, soil type and legume history are valuable for calculating nitrogen fertiliser requirement.
Where to go for expert help
Page last updated: Monday, 27 February 2017 - 12:35pm