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Probe guides soil water estimates and urea decisions

Robyn and Paul Buerckner installed a soil moisture sensor and weather station to monitor plant-available water, rainfall and frost events on their Methul farm in southern New South Wales.
Photo: Nicole Baxter

A moisture probe is taking the guesswork out of plant-available water estimates and proving helpful for guiding urea application decisions on Paul and Robyn Buerckner’s farm at Methul, north of Wagga Wagga, New South Wales.

The couple installed the probe during 2016 through the Mirrool Creek Growers Group, with support from Riverina Local Land Services, to quantify the soil moisture supply in two paddocks.

“Having the moisture probe installed for 2016 showed us the soil profile was full at the start of October, but by the end of that month it was empty,” Robyn says.

“In 2020, above-average rainfall prompted many members to say we were ‘home and hosed’, but I sent out the spring 2016 data just to show how quickly big crops use water.”

During the past four years, Robyn says the probe has proven reliable, which has improved their confidence in using the data to help inform urea top-dressing decisions.

“Instead of basing decisions on gut feel, we look at the data,” Paul says. “We’re still in the lap of the gods in knowing what rain is coming, but we know if soil water is low, we may not see a response to urea.”

When it comes to nutrient management, Paul pre-drills 50 kilograms per hectare of mono-ammonium phosphate (MAP) and 75kg/ha of urea into paddocks earmarked for canola to avoid fertiliser toxicity.

“We’ve seen some seed burn in canola, so now we separate MAP and urea from the seed to improve germination,” he says. “We’ll then add between 75 and 150kg/ha of urea to canola early in its development depending on forecast rain and available soil moisture.”

After cutting hay in 2018 and 2019 because of dry seasonal conditions, and producing high grain yields in 2020, Paul and Robyn are rebuilding the plant-available nitrogen supply.

Deep soil tests are done to keep an eye on the mineral nitrogen supply. Earlier this year, they estimated up to 300kg/ha of urea might be needed on wheat and canola crops if seasonal conditions were favourable.

“I also find grain protein levels of wheat indicate nitrogen levels in the soil and a protein monitor is on my wish list,” Paul says. “Grain falling into the Australian Standard White grade generally indicates nitrogen is maxed-out.”

Paul likes to keep urea rates high because research has shown most of the nitrogen applied will be available for the following crop if seasonal conditions turn dry.

Adjustment was needed to the couple’s nitrogen management strategy after they bought a disc seeder.

“Initially, we had to increase our urea inputs because bigger stubble loads led soil microbes to tie up nitrogen, but the nitrogen cycled back into the system over time,” Paul says.

Read GroundCover article: Time efficiency gain from ‘strip and disc’ system.

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