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Tool to assist nitrogen decisions tested on the ground

To better inform decisions on the nitrogen needs of his crops, Nick Gillett is assessing tools that capture temporal and spatial variability across his paddocks.
Photo: Evan Collis

Nick Gillett and his wife Tryphena farm near Bencubbin in Western Australia. It is a low-rainfall region and crop production can be thwarted by frost. Nick has been quoted as saying it is a region where every one-percenter can improve success with crops and it is this ethos he follows when examining the potential of new technologies.

The Gilletts crop 14,000 hectares, with the dominant crop being wheat and the balance made up of 25 per cent canola, five per cent lupins and 10 per cent fallow. Their rainfall is about 300 millimetres per year but is becoming what Nick describes as increasingly “different”, with the past two years being very good seasons.

Like many other growers, Nick says his main driver for nitrogen application decisions is seasonal potential.

“We usually set wheat crops up at seeding with around 35 kilograms of nitrogen per hectare for our 10-year average, and then we play the season with urea ammonium nitrate solution,” he says.

“Our 10-year average wheat yield is 1.96 tonnes per hectare, but with the recent more-favourable seasons over the last five years we have achieved an average 2.18t/ha.”

Every three in five years the Gilletts’ crops can incur frost damage, so Nick uses a conservative nutrient management strategy.

“We budget at 80 per cent of our yield potential and have not seen any evidence of nitrogen carryover after frosted crops.”

Nick says he is dealing with complex variability both across paddocks and temporally – from season to season – and he was keen to find a means of better monitoring these variations.

Historical records and memories can become distorted.

For these reasons, he was keen to work with Dr Darren Hughes of Laconik on a GRDC-invested National Grower Network project to assess the nitrogen status of his paddocks – in particular, to assess whether there was any carryover of nitrogen from frosted crops.

“Darren’s enabling technology generates pictures of nitrogen status and yield performance across paddocks, seamlessly interfacing with our John Deere variable-rate controller technology on our Gason® airseeders.”

“The technology can then generate swarm trial variable-rate maps across a paddock to test for nitrogen responses that we can easily upload to our system.

“This means we can develop a nitrogen story with both spatial and temporal variability documented for every paddock to better inform our fertiliser application.

“Findings from the first year indicated in the year following a frosted crop we cannot rely upon nitrogen being banked.”

This was illustrated by the grain yield of a crop that followed a frosted crop, which achieved 2.57t/ha with no nitrogen applied, compared to the grower standard of 3.34t/ha with 50kg of applied nitrogen, which is grower standard practice. Applying 100kg/ha of urea would have increased grain yield another 280kg/ha compared to grower practice.

The Laconik technology gives us greater confidence to make decisions on top-dressing during the season and will provide a much more rigorous fertiliser history record for us going forward.

Read also: Can you bank nitrogen in Western Australian soils?

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