After a few areas in Andrew Sargent's paddocks were shown to be consistently low-yielding across a number of seasons, pH mapping carried out earlier in the year has helped shed valuable light on the problem.
Mr Sargent, Brook Park, farms with parents Malcolm and Jane Sargent, cropping 2000 hectares of wheat, barley, lentils, canola and oaten hay at Crystal Brook and Appila.
He could not put a finger on the reason why certain areas of his crops were under-performing.
"There were some old soil tests we'd done a while back, which were showing the potential for some acidity issues, and (agronomist Sam Trengove) also suggested there may be some problems brought about by issues with pH," Andrew said.
"We went back and did some more soil testing in those poor-performing areas, and found that there were some acidic spots, so we ran a Veris pH manager across a couple of those paddocks to test them."
Prior to seeding this year, the pH was mapped for a 200ha paddock in sandhill country, which had acidity issues previously, as well as a 100ha paddock on flat ground with a loam soil type, which had had unexplained yield variations in the past.
Andrew said the results "spoke for themselves" when the pH maps and yield maps were overlaid.
"In places where the pH was low, the 2019 yield map for one of our canola crops was under 0.3t/ha, where yield was better and didn't need liming, we were up to 0.8t/ha," he said.
"We did have a bit of hail damage in that paddock, so it may not be entirely reflective, but the pH maps were basically bang on with the yield maps."
Some of those spots the acidity is clearly at a point where it is affecting production.
- ANDREW SARGENT
The pH in areas that were low-yielding were 4.8 to 5.7 - only just below neutral - and while no liming has yet been done, Andrew intended to lime the areas before seeding next year.
"We haven't limed any of it yet, we didn't get around to it before seeding, but we'll lime it next year, because some of those spots the acidity is clearly at a point where it is affecting production," he said.
He said the lime would be applied at a variable rate, up to 3t/ha.
"There is so much variation in terms of how much lime is needed, it's pretty obvious what you're trying to treat, and the rate will depend on how acidic the soil is," Andrew said.
"We probably won't touch half of the loam soil paddock, the other sandy paddock we'll probably lime most of it, that paddock is generally more prone to acidity, and had an overall lower pH."
The lime will be spread on the surface.
"Incorporating with the seeder would be the hope, but we've got no plans to get out there with a disc chain and work it in, the trade off in soil damage just wouldn't be worth it," Andrew said.
"Especially this sandy paddock, if you went out there with a disc chain you'd want to be pretty spot on, and we'd rather keep the cover rather than till the ground."
In the coming years, Andrew plans to test the soil pH on a yearly basis, testing different paddocks each year, and then liming before seeding in the same year.
Sargent shifts away from VR seeding
MID North cropper Andrew Sargent is using variable rate for liming applications, but he has moved away from VR when seeding each year.
"We got into VR seeding a bit about 10 years ago, and then when we were working out what would be the change each year, a lot of places, what you'd do would be good one year and not so good the next year, so it makes it a bit hard," he said.
"What you do one year might be the opposite to what you do the next year, so overall, you just end up with an average rate anyway.
"We had a lot of issues with equipment, it was a massive hassle, and when you're seeding you just want to get crops in the ground, you don't want to be messing around trying to make it work."
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Andrew admitted VR seeding could be effective, but for him, the benefits did not outweigh the higher level of management required to make the strategy worthwhile.
"You have to do a lot more ground truthing, and there is lot more involved to actually see a return. I don't think it ever saw the levels of adoption that it was touted to see," he said.
Andrew has also used satellite imagery in the past, mainly to check crop performance, and he has also used it when spreading gypsum.
"We based our gypsum spreading off soil cover. We found some Google Earth imagery from when it was bare earth, which helped us make decisions," he said.
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Claire Harris
Journalist at Stock Journal. Hailing from South East Queensland, Claire moved to SA at the start of 2019. She is passionate about agriculture, cooking, sport, and line dancing, and loves a good long road trip.
Journalist at Stock Journal. Hailing from South East Queensland, Claire moved to SA at the start of 2019. She is passionate about agriculture, cooking, sport, and line dancing, and loves a good long road trip.
