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Crop competition from the ground up

Farming in the centre of Western Australia’s southern wheatbelt, Kim and Michelle Slarke use multiple crop competition tactics, including soil amelioration, to reinforce their farming system and weed control program.

Along with their sons, Jamie and Harrison, and their partners Felicity and Tuscany, Kim’s parents and sister, Kim and Michelle are establishing a sustainable cropping system on their 8800 ha aggregation at Lake Grace.

The Slarkes implement several strategies to promote crop competition, including narrower row spacing, higher seeding rates, east-west sowing, variable rate nutrients and soil amelioration.

“Soil health is the number one driver for our business,” says Kim. “We have done our best to respect our soils and improve soil health so our crops can reach their yield potential for the rainfall received. Nearly thirty years ago, we started addressing the low pH of our soils with lime applications.”

Kim says the benefits of the liming program are clear, and they have also applied gypsum to improve the structure of their heavier clays and reduce the hard-setting traits of these soils.

More recently, they have started using a deep-ripping, rock-crushing machine called a ‘Reefinator’, invented by WA farmer Tim Pannell, to increase soil depth and create a good seed bed in ironstone gravel zones where crops had previously struggled to establish.

The Slarkes have found that it often requires up to five passes over a few years to create 160 to 200 mm of soil depth. These gravelly, ironstone areas usually have some clay present, so the process has been very effective in improving crop germination and productivity of these soils. The Reefinator also thoroughly mixes in previously applied lime and nutrients to support competitive crops in previously low-yielding areas prone to weediness. They have almost completed treating the 10 per cent of their farm that requires ‘reefinating’.

They also use a rock picker to collect surface rocks in their paddocks. Removing the rocks and sticks allows them to safely harvest at can height, ensuring maximum weed seed collection.

Over 15 years ago, when the Slarkes started auto-steer farming, they implemented east-west sowing across their farm wherever the topography allowed. This maximises crop competition by using the crop to shade the inter-row space.

Kim says they were convinced by the significant research by GRDC and other groups showing that east-west planting, particularly in cereals, is beneficial for competition against weeds.

“About 95 per cent of the cropped area is sown east-west or close to it, depending on the shape of the paddock and finding a practical AB line for machinery operations,” says Kim. “It was fairly easy to maintain east-west sowing when we removed the fences and established the block farming layout.”

Another aspect of increasing crop competition is using variable rate technology (VRT) to apply soil amendments and fertiliser. They began in 2010 when they purchased an air-seeder with VRT capability. Over the years, they have seen the benefits of addressing soil limitations where they occur in a paddock, lifting the overall yield and reducing gaps in the crop where weeds can establish.

All crops are currently sown on 250 mm (10 inch) row spacing. However, the Slarkes are changing to a wider (24 m) seeder bar and will move to 300 mm (12 inch) row spacing. This will bring advantages, such as better trash flow and less crop damage, as the risk of soil being thrown into the furrow reduces, and a potential disadvantage of more light entering the inter-row, allowing weeds to establish.

Over time, the Slarkes have increased their cereal seeding rate from 50 kg/ha to around 70 or 75 kg/ha to increase the crop’s competitive advantage against weeds.

Since selling the last of their sheep in 2018, they have implemented a block farming system where blocks of up to 2000 ha are sown to a single crop species. Removing fences has eliminated one of the farm’s primary weed sources and maximises machinery and labour efficiencies.

The Slarkes back up their farm-wide weed control tactics with all the other WeedSmart Big 6 strategies, including harvest weed seed control with a Seed Terminator, a multi-pronged herbicide program and diverse cropping rotation.

The WeedSmart Big 6 strategy embraces herbicide and non-herbicide weed control tactics to keep weed numbers low in cropping systems. The latest weed control tactics and technologies will feature at WeedSmart Week in Port Lincoln on 2930 July 2024.

Read about the Slarkes’ approach to block farming and spray efficiency.

Read the Slarke’s Big 6 case study.

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