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.”

Farmers change practices to improve Great Barrier Reef health

AN Innisfail sugar cane farmer has reduced his fertiliser use by 20 per cent, without affecting yield.

Third-generation cane farmer Sam Spina, who farms alongside brother Michael, said implementing simple changes had both increased profitability, while providing beneficial environmental outcomes.

Mr Spina started making changes two years ago, planting bean fallow crops and varying fertiliser application rates across his paddocks.

The results have been pleasing, with the brothers reducing fertiliser use from 160kg per hectare to 120kg per hectare – a reduction of 20 per cent.

Mr Spina said he had started planting bean fallow crops two years ago with the help of a new tractor partly financed through the Reef Trust IV program.

He said as a small farm, they would not have been able to do so without the program delivered by the Wet Tropics Sugar Industry Partnership.

“As a small farm we couldn’t have afforded it otherwise,” he said. “We re-plant cane on

four to five hectares and plant beans on the same number of hectares each season to

increase the nitrogen in our soil in a more natural way.”

He then accessed an all-of-farm nutrient management program, also developed by WTSIP officers last year as part of a free service to growers.

“We had a really good look at the soil tests and matched the fertiliser blend to those tests,” Mr Spina said.

“We changed fertiliser and reduced it, and experienced no productivity losses.

“We’re still up around 90 tonnes (of cane) per hectare, depending on the weather and the season.

“We saw in the soil tests that some paddocks needed more super phosphate in the ratoons so we also changed that.

“Our fertiliser box is on GPS now so we can automatically adjust the rate as we go.”

The family’s farm is about 1.5km from the Johnstone River and 8km from the ocean, and Mr Spina said they had also laser levelled their land and reshaped drains to help improve water quality.

“Laser levelling helps to produce a more even crop and it’s also helping with water quality,” he said.

“With the grassed headlands and drains as well, when the water runs off the paddock it moves slowly and goes into the spoon drains first so any sediment can settle.”

Mr Spina said changes that began as cost-saving initiatives had become much more as growers became more environmentally aware.

“Over the years cane growers have become a lot more aware environmentally – we’re grassing our headlands, trash-blanketing, applying fertiliser underground, getting water samples.

“If there is fertiliser coming off our paddocks, we want to know about it so we can fix it.”

The Spinas are one of 39 Wet Tropics growers to receive tenders to reduce fertiliser use on their farms.

WTSIP chair Joe Marano said one the main benefits of the system was that growers could choose the practice changes they believed would be most effective on their farm.

“They’ve been trialling a range of different ways to reduce nitrogen – from using controlled-release fertilisers or applying mill mud to growing legumes as a source of nitrogen and buying specialised equipment,” Mr Marano said.

“These growers have been able to reduce their use of nitrogen fertiliser without affecting their yields – a good result for profitability and for water quality.”