Soil testing and weed mapping: the ultimate partnership for healthier pastures

Agronomy and pasture consultant Lucy Powell said what’s happening below the surface is just as important as what’s growing above it when it comes to improving long-term pasture productivity. 

Based in Julia Creek in north-west Queensland, Lucy works with producers across Queensland and NSW. Throughout her career, she’s seen the significant value in establishing baseline soil data and tracking changes over time to support informed decision-making.

Lucy said there’s often an additional factor of weeds competing against northern pastures for soil moisture and nutrient – further impacting grazing land productivity.  

Together, these factors highlight an opportunity to strengthen data-driven decision making, as producers work to better understand and manage what is happening within their soils and pastures.

Here, Lucy shares her insights into how combining soil testing with strategic weed management – and using that data over time – can help build a clearer picture of pasture performance and support long-term productivity.

Soil testing for pasture insights

While local knowledge plays an important role in managing on-farm production, Lucy said, without data to support that knowledge, it often relies on the assumption that the land condition doesn’t experience any gradual decline.

“It’s very hard to manage what you don’t measure,” she said.

“Rainfall, cattle, weeds – they all contribute to changes in soil distribution and nutrient levels.

“Soil testing provides a clear baseline, allowing producers to make more informed decisions and target inputs where they’ll have the greatest return. 

“Without that baseline, opportunities to better understand system performance and guide future improvements may be missed.”

Given the scale and diversity of northern properties, Lucy recommends a strategic approach.

“Rather than initially testing every paddock, producers should identify representative management zones based on factors such as soil type, pasture species and grazing pressure,” she said.

“Within these zones, taking multiple soil cores helps build a more accurate picture, while GPS marking sample sites – something as simple as dropping a pin – allows producers to return to the same locations over time.

“This consistency is key to tracking changes, identifying trends and assessing the impact of management decisions.”

According to Lucy, there’s no single “right” time to start soil testing.

Instead, consistency is key – establishing a repeatable sampling approach allows producers to build a baseline, track changes over time and better understand how management and seasonal conditions may be influencing productivity.

“This approach can be particularly useful for monitoring changes over time and supporting management decisions, even in native pasture systems where fertiliser use remains minimal.

“As production systems continue to evolve – particularly with increasing integration of improved pastures and forage cropping –the value of timing and repeat testing is only likely to grow.

“For now, establishing consistent, repeatable sampling is the most important step.”

Weeding out pasture challenges

Weed pressure is another major challenge for northern beef pasture systems, with species like prickly acacia, parkinsonia, rubber vine and bellyache bush competing directly with productive pasture for soil nutrient and moisture.

Lucy said it can be particularly challenging in northern regions, where infestations can establish and spread quickly if not actively managed.

Similar to improving soil condition, Lucy said the first step to combating this challenge is collecting data.

 “Knowing your weed burden is crucial,” she said.

“Mapping weed infestations – along with identifying high-risk areas such as waterways, yards or heavily utilised zones – are key to helping you prioritise control efforts.

“Over time, it can also help you see how effective your weed management strategies are – identifying areas that are either improving, or becoming more overrun.”

While chemical control often forms the backbone of weed management, Lucy said it should be combined with mechanical removal where practical and supported by grazing management strategies where appropriate.

“Timing depends on the specific weed and its growth cycle, meaning there is no one-size-fits-all solution,” she said.

“Ongoing monitoring is key, particularly following seasonal rain when growth can accelerate.

“While weed control is an ongoing part of grazing land management, improving soil condition and pasture productivity can make a significant difference over time.

“Healthier, more competitive pastures leave less opportunity for weeds to establish, helping to reduce pressure and make management more effective.”

Turning data into better feedbase outcomes

For Lucy, the path to stronger pasture performance starts with closing the gap between observation and evidence.

“Bringing together soil testing and weed mapping as part of your grazing land management plan creates a more complete picture of how a system is functioning – and where improvements can be made.

“Over time, this more informed approach can create a positive cycle – healthier soils supporting stronger pastures, and more competitive pastures helping to reduce weed pressure.”

Combined, Lucy said these fundamentals form the basis of more confident, data-driven decision making and long-term success in northern grazing systems.