Deep soil insights key to better cropping returns
Beth Sleep is on a mission to reveal what lies beneath the topsoil and unlock the potential of under-performing cropping zones through soil science.
The young agronomist at Elders Jamestown has been offering fee-for-service soil consulting for the past year, allowing growers to better understand their data and manage their soils for profit.
“Soils change as you go down the profile, literally centimetre by centimetre, as a result of land form processes, parent material, topography and continued introduction of salts and other elements with every application of agricultural inputs,” Beth explained.
As every farm is different, Beth always starts by asking growers to set an objective and works back from there to achieve positive outcomes.
“Through soil consultancy I can help farmers understand what they’re working with and improve cropping management zone by zone for better returns on investment by spatially matching inputs to localised soil conditions and yield potential,” she said.
“This is becoming more important with input prices increasing rapidly.”
Head of Technical Services, Graham Page, said that a greater understanding of soil is a major component of the precision ag puzzle.
“We are living in an age of big data, but there’s still a lot to learn about how to use this data most effectively,” Mr Page said.
“It takes someone with a good agronomic understanding combined with soil knowledge to make sense of it, explain what’s driving the variability and give growers the power to make educated, confident management decisions that result in good returns on investment.
“Having a better knowledge of the drivers simplifies decision making and takes away a lot of the in-season stress of making decisions without knowing all the information.”
According to Beth, growers often enquire about soil consultancy to make sense of the variability in their yield maps.
A lot of the time, she says it comes down to classifying different zones in the paddock and developing different strategies for each zone to manage yields.
“It could be a zone that is performing well, at its most productive capacity, so all that is needed is to maintain it and not mismanage it longer-term to sustain good yield potential.
“Taking actions like making sure the nutrients that are being removed are replaced, and that maintenance lime is being used to counteract acidification from cropping when needed.”
Then there are zones that are under-performing.
“An under-performing zone may already be too acidic, or it may need additional phosphorus because the crop has been taking more than has been put back, or it could be compacted, but there’s something we can do to improve it and boost yields,” she said.
“Lastly, there are those zones which perform much worse than the rest of the farm because of a soil constraint that can’t be fixed. This may be an eroded soil with high concentrations of free lime, locking up nutrients and reducing rooting depth.
“What I aim to do is relocate the resources used in this zone, where the return on investment is typically very poor, to zones where the crop can use those inputs to boost or maintain yields and profits. The last thing we want to do is feed these areas for no returns.
“Phosphorus is a good example here, because historically a lot of growers used a replacement rate based on their average yield. If the average paddock yield is 4 t/ha, but one patch is only yielding 1 t/ha, the grower is essentially throwing away enough phosphorus for a 3 t/ha crop and that’s accumulating in the soil every year.
“It’s a big expense, especially now, when fertilisers are around double to this time last year.
“Meanwhile, zones that are achieving better than average yields, say 6 t/ha, are only receiving enough replacement phosphorus for 4 t/ha crop. The soils in these areas will slowly be declining in phosphorus, reducing yield potential over time.”
Another common reason behind yield differences is landscape. For example, Beth explained that on eroded hilltops, yield potential is usually severely limited.
“These areas have typically lost all their topsoil to lower lying areas through the decades when cultivation was popular,” she explained.
“If the topsoil has moved down the hill, why not move most of the inputs down there too, because that’s where the yield potential lies?”
While it’s rarely this simple, Beth works with growers to identify the numerous interacting factors at play before recommending changes.
Getting to the truth
An agronomist’s investigative work is methodical, taking into consideration existing data as well as ground truthing to pinpoint problems. It looks to refine the information with more strategic mapping or testing.
After initial investigation, it often only takes one or two more high resolution maps to reveal the rest of the story.
“I am wary of over-complicating the process by taking numerous maps upfront which can just cloud the story as well as being an unnecessary expense for the grower,” Beth said.
Instead, she collects all the maps and data the grower already has available to learn as much as she can from it, looking for trends across the paddocks and ruling out environmental variability, such as areas which regularly suffer frost damage.
“One problem I find with the data is it is only as good as the way it is collected,” she said.
“For example, if all the soil tests are taken at the topsoil level in a paddock with subsoil constraints, or in parts of the paddock where there are no issues, the results will probably show that the soils are fantastic.
“But it’s not telling the whole story of what’s going on in the subsoil, where the plant’s roots will be in springtime when the grain is filling.” she explained.
What Beth can’t explain from her desk, she investigates in the paddock.
“I go into those patches that I can’t explain from machinery error or environmental factors and take a deep soil core,” she said.
“This soil core goes up on my ute tray where I can characterise it for texture and different yield limiting constraints that may be present and figure out what’s driving yield or limiting yield in that patch.”
Another thing she looks at is the crop roots.
“The plant roots tell me a lot because if they stop or start to grow laterally, then I know exactly where I need to look, because there’s obviously something preventing them from growing deeper,” Beth said.
“Our biggest limitation in this area is moisture, so if we can get plant roots down deeper, they’re potentially exposed to more moisture and can produce more grain at the end of the year.”
Further information may be needed, but then she knows exactly where to investigate, making the investment in testing or scanning paddocks much more targeted.
Managing for long term sustainability
“Ultimately, I’m helping growers achieve the optimal yield in every zone,” Beth said.
This shouldn’t be confused with evening out paddocks to create consistent yield across the whole paddock.
“I am looking to reach a point where every area of the paddock is economically optimised, and this often means poorer areas are not fertilised as much, hence the yield remains low in those areas,” she said.
“Improvements come through a process of picking off the low hanging fruit that will give the best yield improvements for the investment, and then picking the next highest fruit until we’re managing each zone to achieve its optimal yield.
“At this point, decision making is made really easy. The grower knows what is achievable in each patch of the paddock and we can work back to get an exact investment that should be made in that patch for each season. It will still vary between seasons, with clays performing better in wet years and sand in dry years, but we will have that knowledge at our fingertips.”
With ever increasing cropping input prices and land values, Beth said growers were very keen to make the most of their existing cropping area and stop leaving attainable yield on the table.
“Growers are taking more interest in their soils. Professional consultation can help them understand their soils, their limitations, how to avoid wasting expensive inputs on areas that won’t respond, and where they can increase inputs to get a better bang for their buck,” she said.
“The other day I was talking with a young grower who was saying his grandpa used to fence the farm to soil type. But now with modern practices and machinery, paddocks are becoming bigger and bigger and as square as they can possibly be, and this is introducing a lot more variability and complexity in soil management.
“If I can help explain why that variability is there and how growers can manage it sustainably, that’s a big step forward.”
For advice you can trust, speak to your local Elders agronomist.
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