Soil health key to reducing fertiliser rates

Ask cane grower Robert Bonassi how he’s slashed fertiliser rates without affecting yield and he has two words – soil health.

The third-generation farmer is focused on fallow crops, mill by-products and soil tests in his transition to cane that is less reliant on artificial fertilisers, and he says the journey has been both challenging and rewarding.

Mr Bonassi is one of 39 Wet Tropics growers to take advantage of the Australian Government’s Reef Trust IV tender program, delivered through the Wet Tropics Sugar Industry Partnership. The program is helping to finance changes reducing fertiliser use on these farms, and potentially other farms in the future.

The Ingham grower cut his fertiliser rates by up to 20 per cent over four years – moving from 160kg of nitrogen per hectare to 120 – 130kg for plant cane and 145kg for ratoons.

He said the take-home message was simple – you need to maintain healthy soils.

“I’ve learned you can’t drop the ball – you’ve got to keep the soil healthy when you’re reducing nitrogen and phosphorous,’’ he said.

“We’d always taken soil samples but now we target every block we fallow on a yearly basis.”

The Bonassi family grows cane on 180 hectares over four parcels of land, with 25 of those hectares under fallow crops at any given time. They moved to mounded rows and zonal tillage to solve waterlogging issues in the wet season, manufactured a zonal ripper and mounder, and bought a bean planter last year.

soil health

They are also sold on mill mud and mill ash for its nutrient and soil conditioner properties.

“We apply sub-surface mill mud and ash in the fallows. Slowly, slowly it is building our soils up and helping us with reducing our fertilisers,” Robert said.

“Living 35km from the mill we needed to think about ways to reduce costs, so we get it bulk-delivered and we bought our own spreader. Now we can control the rate. We spread zonally at the end of every year, using about 80 tonnes to a hectare. We can target where we put it depending on the state of the ground.

“Within five years we’ll have gone across the whole farm with 80 to 100 tonnes per hectare of mud and ash and we should start seeing results. Then we’ll look at halving that and see if we can still meet the nitrogen levels.”

He said the regular soil tests also helped to maintain calcium and magnesium levels, with lime applied when needed.

“At this stage we’re not saving money but our yield hasn’t been affected and overall it feels like we are getting there,’’ he said.
“This is something I’ve always wanted to do – get the soils back up.”

His farm is 6km from the ocean “as the crow flies”. Two of the parcels of land have three creeks running through them and one shares a boundary with national park land.

The Bonassis constructed silt ponds a decade or so ago with the help of another Federal Government Reef grant and most of their drains run into them. They have spoon and grassed drains to slow the flow of water off the paddock.

“It’s all about getting a good balance – good returns on the soil while minimising run-off to the very best of our ability,’’ he said.

“I always remember visiting an older farmer on a trip in my late 20s as part of a Young Farmers group. That was more than 25 years ago and he had already moved to 1.8m rows. He told us if you’re making changes, give it 110 per cent. That’s what I do now. What worked well last year doesn’t always work well this year, so it keeps you on your toes.”

Wet Tropics Sugar Industry Partnership extension officer Jarrod Sartor said incremental change was the way forward for growers.

“An important message when reducing fertiliser is not to drop it by too much too quickly or without fixing other constraints, or you risk losing productivity,’’ he said. “By regular soil testing, ameliorating with mill by-products and lime and using legumes as a break crop, you can constantly improve the soil to better use the fertiliser being placed.”

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