GRDC Northern Panellist Jack Williamson
In dry seasons like the one we’re currently experiencing, it can be a challenging task to decide if, when and how much nitrogen to apply before winter sowing.
That process normally begins with soil testing, calculating the amount of nitrogen needed for the crop to reach a farmers’ target yield and protein, and available cash after a frosted 2013 winter crop and a scorching summer period which saw summer crop yields suffer.
Most farmers in this region would prefer to then apply their nitrogen to soils with a full moisture profile to maximise the benefit to the crop of their fertiliser investment. This also reduces the risk of waiting for an in-crop rainfall event that may not arrive later in the season when rainfall events are traditionally more unreliable.
However, due to the lack of summer rain, grain growers may need to re-assess their preferred approach and prepare ‘Plan B’.
That decision will have to be made sooner for some than others – many growers ordered urea six months ago when prices were low; they now need to decide whether to accept those orders and apply their usual rate to their full farming area, or let those early orders go and take more expensive product when it does decide to rain.
The upside of applying nitrogen in dry conditions is that it will remain in the soil until activated by rainfall and infiltrate down the profile, whereas applying fertiliser N to a full moisture profile can lead to high gaseous losses through ammonia volatilisation and denitrification in the event of further heavy rainfall and waterlogging as it has nowhere to go.
But some farmers are reporting plant available moisture levels of only five per cent, which has them re-thinking whether or not to sow at all.
In order to manage risks and minimise exposure to potentially losing their fertiliser investment, it may be worth considering only fertilising a portion of the intended sowing area, or splitting the fertiliser application, with a reduced rate applied at sowing and a second application in-crop.
While splitting the application is a more expensive approach depending on the product and application method and the opportunities for incorporating nitrogen in-crop are fewer due to the scarcity of winter rainfall events, it is a lower risk strategy and allows farmers to time their fertiliser investments in line with when those rainfall events occur.
The key issue farmers need to understand in working through these scenarios is what level of risk they are comfortable with.
A number of tools are available to growers to help them work through these decisions, including the booklet Managing Legume and Fertiliser N for Northern Grains Cropping, which is available from the Grains Research and Development Corporation website.
The Climate Kelpie website, www.climatekelpie.com.au, also offers a Nitrogen Fertiliser Calculator designed to assist farmers in projecting the likely crop yield response to nitrogen for a given starting soil moisture and regional rainfall projections.
GRDC Northern Panellist
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Cox Inall Communications
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