7 minute read
Evolving landscape
BY RENEE CLUFF
Re-established water courses and fine-tuned nutrient management are improving the quality of runoff to the Great Barrier Reef.
The cane fields of lower Mirriwinni and Babinda, south of Cairns, are bordered by a network of deep drains. The channels were first established in the 1960s by sugacane growers seeking to counteract the combination of the area’s extremely high rainfall and its swampy landscape.
Max Wilkins, Chairman of the Babinda Swamp Drainage Board, grows cane on around 450 hectares in the area with his brother. He’s a third-generation farmer whose grandfather began working the land in the 1920s.
“We were the first ones to dig a big deep drain every 40 rows to get rid of that water underneath,” Max said. “Without the drainage scheme, cane growing in this area wouldn’t exist.”
His neighbour, Barry Stubbs, has also farmed in the area all his life and clearly recalls the transformation from boggy ground to productive cane fields.
“It’s taken a long time,” Barry concedes. “It was all swamp land.
“I remember we were cutting with the old Toft harvesters with rubber wheels. When they’d pull up for smoko, they had to swing the elevator around on the hard ground, pull up on the headland and find a hard spot because otherwise, it would just sink in front of your eyes – it’d go down.
“But to see it now, compared to what it was back then, you wouldn’t recognise it as the same block. It’s all through drainage.”
Once again, the landscape in this area is changing, motivated by sugarcane growers on a mission to improve Great Barrier Reef water quality.
The growers are involved in the $6.2-million Mulgrave-Russell Water Quality Program, funded by the partnership between the Australian
Government’s Reef Trust and the Great Barrier Reef Foundation. The program, managed by the Reef and Rainforest Research Centre (RRRC) and coordinated by CANEGROWERS Cairns Region, encompasses two projects.
Agronomy solutions provider Farmacist has provided extension support and nutrient management plans to growers involved in its Precision to Decision initiative, while the water quality monitoring and drainage remediation project has been delivered by James Cook University’s (JCU) TropWater.
Combined, the works are contributing to a regional reduction of 72-tonnes of Dissolved Inorganic Nitrogen (DIN) from entering the Reef’s waters each year.
Grower Barry Stubbs said the drainage arm of the program stemmed from the results of water quality monitoring at local farms, which highlighted the importance of the ‘first flush’ of the wet season in decreasing nitrogen runoff.
“During all the years of monitoring water quality as part of Project 25 (led by JCU TropWATER and funded by the National Environmental Science Program), the results of DIN losses have always come up the same,” he said. “We found losses are directly linked to weather patterns and are highest during the first rainfall of the wet season.
“We learned that if farmers can put the fertiliser on relatively early, and if we don’t get a big rainfall period until say Christmas, the risk of nitrogen runoff is reduced.”
Barry has also installed back-up systems to further decrease the risk of DIN runoff to the Reef, particularly in the case of early rain.
“We’ve put in settling ponds because we’ve found out that if you can slow the water down, even for a short while, it helps break down and transform nitrate before it reaches the Coral Sea,” he explained.
It’s just bringing back what nature had here before
The Mulgrave-Russell Water Quality Program is now taking the ‘first flush’ learnings catchment-wide. It is diverting farm runoff from the main drain systems through water retention basins, to allow denitrification to occur on land.
In Barry’s Russell catchment, the original lagoon system that ran through a nearby cattle property is now being reconnected to divert the first flush flows from the drainage network.
“We’ve had the excavator down there cleaning it out and we’ve just got to get the levels right and we’ve got to put a little diversion in off the main drain,” he explained.
“When we get a storm, that first rain will go through there. The first flush we capture will be taken on its natural journey through the old lagoon system, allowing it to meander and settle. It’s a reinvention of the natural environment.
“We now just need to fence it off from the cattle and plant riparian vegetation along it. A lot of good has come out of this and I think it will be replicated along the coast where possible.”
The water retention project saw a similar basin established at Aloomba in the Mulgrave catchment. JCU TropWATER researcher Aaron Davis worked closely with local growers to establish where opportunities for drainage intervention existed.
CANEGROWERS Cairns Region Environment and Sustainability Officer Joel Tierney said the work is a demonstration of the need to build on learnings from previous water quality initiatives.
“Aaron Davis has been involved in water quality monitoring in this area for many years and the growers know and trust him and they trust his results,” Joel explained.
“You don’t want all that investment to go into one project and then drop off, especially when you’ve got all these growers engaged.
“We can only reduce fertiliser rates on farms so much and actually maintain productivity. That’s where moving to this first flush retention idea is the next step in how you can manage water quality and hold back any DIN losses to that whole-of-catchment scale.
“Your return on investment is going to be a lot better than if you were just focusing on one paddock.”
The program’s agronomy extension project focused on fine-tuning agricultural practices and inputs.
It gives you more bang for your buck
Farmacist’s Precision to Decision delivered tailored Nutrient Management Plans and extension services to 84 growers across more than 8,000 hectares. The aim was to better match inputs with crop requirements at a zonal level.
Grower Max Wilkins has a long history of practice evolution which he believes can be attributed in part to the thriving fish populations he sees in his drains. Max is also credited with introducing the concept of lime amelioration to the region many decades ago, when he noticed that no matter how much he increased fertiliser applications, cane yields were continuing to decrease due to the acidity in his soils.
While history clearly illustrates the success of his resourcefulness, Max has not rested on his laurels. Even as he approached his eighth decade, the Miriwinni grower retained his drive to keep learning through involvement in Precision to Decision.
He worked alongside Farmacist’s Extension Agronomist Shannon Byrnes, who took soil samples from his farm and established nitrogen rate trials, among many other initiatives.
“Pretty much anywhere in the Wet Tropics I would say you have really acidic soils, so you don’t get your full fertiliser utilisation – the plant can’t take nutrients up because they’re not available due to the pH,” Shannon explained.
“But in Max’s case, because he has such good pH and such a good, long history of lime application, the crop was unrestricted so you could get a beautiful nitrogen response curve in the trials.
The yield plateau was really obvious
“With Max, it was more about finding the product and rates that work across the farm. You want to be tailored to the block, but you don’t want to have 10 different products to deal with.
“It’s finding that balance between what’s needed and what’s practical.”
Precision to Decision is due to wrap up at the end of next month, while the controlled drainage project continues until June 2025.
