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Testing time for maize fertilisers to optimise yields

Victorian maize grower Ray Thornton is conducting nitrogen application trials in an attempt to maximise his yields.
Photo: Catherine Norwood

Long-time Victorian maize grower Ray Thornton has set up his 2024 maize crop for an 18-tonne-per-hectare yield, applying up to 350 kilograms of nitrogen during the season – most of it up-front.

Soil tests indicated that 60kg of nitrogen was available in the soil, and another 75kg would become available as nitrogen mineralised during the growing season. His applications of 350kg provided a 485kg total for the crop.

Ray says these in-soil and mineralisation calculations are essential in providing enough fertiliser, but not too much, given the ongoing battle to reduce farm inputs while optimising yields.

When the results of recent GRDC trials suggested re-evaluating fertiliser rates, it prompted Ray to set up an unofficial trial to test rates on his property at Waaia in northern Victoria.

The recent trials were conducted as part of the GRDC ‘Optimising Irrigated Grains’  project, which included three maize trials at Kerang, Victoria, and three at Finley in southern New South Wales from 2020 to 2023.

Based on soil conditions at Kerang and Finley, including available nitrogen, potential mineralisation of nitrogen during the growing season, and different nitrogen application rates, yields were optimised with 240kg/ha of additional nitrogen.

Three nitrogen application rates tested

Ray is a member of the Irrigation Farmers Network (IFN), the farmer-based research group that conducted the Kerang trials. In his own on-farm trial, he is testing this year’s fertiliser regime with three nitrogen application rates similar to those of the IFN trials: 140kg/ha, 265kg/ha and 290kg/ha, each applied to several rows of maize.

More than 40 people attended an IFN farm focus group at Ray’s property earlier in the year to share findings from the ‘Optimising Irrigated Grains’ project, to view the fertiliser trial and learn about Ray’s corn cropping experiences.

Fertiliser rates proved one of the hottest topics with growers, who can apply more than 400kg/ha to boost soil nitrogen and crop yields.

On the day of the focus group in February, the three trial treatments showed a higher proportion of dry matter compared to Ray’s crop.

“But the proof will be in the harvesting,” Ray says.

Whatever the result, the trials suggest that we need to test recommendations on our own local soils and conditions, even if that’s just doing a few rows with different treatments.

“What works in Kerang might not work in Waaia, or somewhere else,” he says. (Results will be available from the IFN, following the harvest in April.)

Ray highlights his own experience with water-run urea, a widespread practice in irrigation areas where urea is added to channel water as crops are irrigated.

He had refined his water-run urea application techniques over more than 20 years. But when he took part in an irrigation water use efficiency trial 10 years ago, he discovered that potentially up to half of that urea was wasted compared to direct crop applications, with a 2t yield penalty.

From that point on he has switched to in-crop applications only for fertilisers, which he continues to test and revise.

He also works to constantly improve his soils with precision agriculture techniques that allow him to leave the often-substantial maize stubble in place to break down and build organic matter and soil carbon, planting between rows in alternating years.

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