LANGHAM — In a four-foot-deep soil pit, geological history is clearly defined.
The layers tell the story of how, 10,000 years ago, glacial movement pulled clay, silt, salt and lime across the Prairies. They display the very reason for the landscape’s agricultural productivity and fertility.
“All of the soils here in the Prairies are influenced by glaciation, with the exception of the tops of the Cypress Hills,” said Jeff Schoenau, a soil scientist and program chair in soil nutrient management with the Saskatchewan agriculture department.
“But in this case, the glaciers, when they melted, left behind a glacial lake. And what was in that glacial lake? Clay. And as that clay settled out, it went to the bottom, and it produced this parent material that we see here.”
That parent material has given rich soil to much of the Canadian Prairies.
Why it matters: Knowing a field’s soil composition allows for better decisions regarding soil health.
Schoenau identified the various layers of soil composition at a Crop Diagnostic School in Melfort, Sask. The A horizon is prime topsoil, shown in a clear, defined line. Good topsoil is 15 to 20 centimetres deep, he said. The C horizon contains calcium carbonate, or lime, that when sprayed with hydrochloric acid, bubbles and produces carbon dioxide gas.
“If you measure the pH of this soil here, the parent material with all that free lime, the pH would be around 8.5. Anytime you get that effervescing or bubbling, that tells you you’ve got a soil with a high pH.”
The reaction only occurs in the lower layers, where minerals have become more concentrated over time.
“Water moving through has leached that carbonate down. And also plants, microorganisms have added organic matter that’s turned into humus that’s created these layers or horizons in the soil.”
Organic matter matters
Organic matter is the most important factor within a soil and most necessary to measure, said Schoenau. It’s a key part of healthy soil, exemplified in the Melfort topsoil, which has eight to 10 per cent organic matter. That’s the highest percentage in the province. Without it, a soil may become entirely C horizon.
“High pH, low organic matter, not very productive at all,” he said. “(It’s) common on eroded knolls. Seen in the 1930s, all that wind erosion, water erosion, sins of the past, so to speak. And we lost all that topsoil.”
Carbon storage and natural nitrogen production rely on organic matter . Approximately 95 per cent of a soil’s natural nitrogen is contained within organic matter, and that nitrogen can work out to roughly 10,000 pounds per acre within 15 centimetres of topsoil.
But plants can’t take up nitrogen directly. They require microorganisms to cycle soil nutrients and convert nitrogen into ammonium nitrate through organic matter decomposition and mineralization.
Schoenau had research-based solutions for fields lacking organic matter and the accompanying microorganisms.
“One treatment was manure. Another treatment we had was biochar, it’s kind of like a synthetic organic matter. Another treatment was commercial fertilizers like phosphorus, copper and zinc micronutrients, because often those eroded knolls are particularly low in available phosphorus, also micronutrients as well. So, we had those alone and in combination.”
The control treatment was topsoil replacement, applied by moving soil that was eroded into low areas onto areas with high pH and low organic matter.
“Manure as an amendment was the most effective, but with our upper-level control, the high end was the topsoil replacement, really showing the value of topsoil and keeping it in place,” Schoenau said.
He also discussed soil compaction, an issue often faced in the Melfort area and Red River Valley due to the soil’s high clay content. Clay is fantastic, he said, especially when paired with organic matter, because it retains moisture to carry a crop through dry periods.
But compaction increases soil density and strength, sometimes to the point that roots can no longer penetrate. Whether a soil is naturally dense or a result of high field traffic, the issue can be dealt with biologically or mechanically.
A forage or cover crop can help by breaking up the soil and increasing organic matter. It can also draw groundwater, especially if the crop has taproot systems. On the mechanical side, Shoenau said a subsoiler with a fairly narrow-profile shank and minimal surface disturbance proved effective.
“But at the bottom of those shanks is a kind of plow shear run at 30 centimetres, creating a lifting action, a loosening action that significantly reduced the density and reduced the soil strength.”
The mechanical approach is best used as precision tactic in the most deeply compacted areas, rather than an entire field. Schoenau said addressing the whole field is not the most economical solution. His research showed only a small overall yield increase of five per cent compared to spot use, where there were significant increases of 15 to 20 bushels per acre in canola.
“As we’re dealing with increasing land values, people are looking at ways that they can improve the productivity of the land base that they have got,” Schoenau said.
Related
About the Author
