Nitrogen source and timing under cold conditions

By: Mark Tucker

The first nitrogen application to cereals is the most rewarding so it is important to make the right decisions when it comes to nitrogen source and timing, especially under cold conditions.

Nitrogen source and timing under cold conditions
Nitrogen source and timing under cold conditions
Early nitrogen decisions need to balance risk vs reward

The first spring nitrate nitrogen applications to cereals are the most rewarding, with an average on wheat of 33.8 kg grain per kg N leading to a healthy return on investment.

This first nitrogen application is the most important, setting the foundation for a successful harvest. In view of this, management practices should be adopted that do not put this reward at risk. Understanding why this nitrogen application is so important helps to ensure the right decisions are made.

Yield response to first 100 kg N/ha in winter wheat

Biomass growth limits yield potential

As cereals come out of winter it continues to grow new leaves and tillers, and with every leaf initiated, a new root is initiated. Typically 50 – 60% of the above ground biomass (leaves and tillers) that develop will be converted into grain yield (the Harvest Index), and of course a large root mass creates resilience to possible drought periods during the spring and summer months ahead, as well as ensuring maximum nutrient use efficiency.

However the period for this biomass growth is time limited as at a critical day length (typically the 20th March) the wheat plants switch from vegetative to reproductive growth and the ‘potential’ total biomass has been determined.

Nitrogen must be immediately plant available 

Decisions now that can affect this foundation building growth period centrally revolve around the choice of nitrogen source, rate and timing. The right source of nitrogen needs to be in a form that is immediately available for crop uptake, ensuring growth and development is not restricted.

Nitrate nitrogen as in YaraBela Axan is immediately available whilst urea needs to go through transformations before being crop available. Transformation is a biological process and thus dependent on a number of factors of which soil temperature is a key one. Currently soils are still at 2°C, half of where it would normally be.

At low soil temperatures urea is less available than nitrate

At this temperature the first transformation of urea to ammonium will take around 4 days, whist the second transformation from ammonium to nitrate could be over 6 weeks. Weather data also informs us that March and April are typically the driest months, during which nutrient demand is at its peak as crop biomass accumulates.

The best management decisions are well informed decisions, and the greatest chance of survival comes from ‘adaptation’ as Darwin taught us. With this in mind now is the time to reflect on decisions that will influence the yield potential you are now establishing, and how you can adopt ‘best practise’ to realise this potential.

Nitrate nitrogen fertilisers supply an immediate form of available nitrogen, with minimal losses, producing highly efficient crops with large root system’s that bring overall nutrient use efficiency gains.

More information on YaraBela nitrate fertilisers

Read about improving nutrient efficiency

Wheat agronomy and fertiliser advice
Wheat agronomy and fertiliser advice

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