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
Paddock
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.
Plant
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.
Where does it occur?
Temperature
Soil type
Wet conditions
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.
Management strategies
Spraying foliar
Soil application
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?
Tissue test
Soil test
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.
