Plants draw different amounts of moisture from different depths in the soil, and growers can make those differences work for them
Grain farmers are always hoping for a Goldilocks year — not too wet, not too dry, but just right.
But since fairy tales rarely come true, researchers with Manitoba Agriculture, Food and Rural Initiatives are looking for alternative approaches.
“It’s led us to wonder how we might weatherproof our crop rotations a bit,” oilseed specialist Anastasia Kubinec told the recent opening day of the Manitoba Crop Diagnostic School.
“One place to start is to talk about what’s going on below the surface, rather than just what we’re seeing above ground.”
Simply put, there’s an enormous variation in the rooting depth and function of common field crops. Plants draw different amounts of moisture from different depths in the soil, and growers could potentially put those differences to work for them, Kubinec said.
“Growers in a part of the province that’s recovering from wet conditions, or someone with soils that are chronically wet, might want to look at a crop like sunflowers,” Kubinec said. “They root very deeply, down to seven or eight feet, with a well-developed tap root. They also use a lot of moisture, up to 1,000 millimetres a season.”
Thirsty crops, such as sunflowers, can not only survive wet conditions, but also soak excess soil moisture and give crops that like drier soil a better chance at success in the subsequent crop year.
On the other had, if things are too dry, shallower rooting crops with lower moisture needs might be a better bet. Flax, for example, has a fibrous and shallow root system that only goes down about 76 millimetres and its water use is just one-third of sunflower crops (340 to 440 millimetres a season). Navy beans are also a shallow-rooting, low-water-use crop.
As well as keeping an eye on the rooting and water use basics, there’s also the issue of what else is present in a field. The presence of a Group 2-resistant green foxtail population in one plot area that escaped control measures prompted a discussion about how it competed more with shallow-rooted crops.
“If you look at flax, we found it rooted to 25 centimetres, and the green foxtail rooted to about 23 centimetres — they’re basically rooting to the same depth in the soil profile,” Kubinec said. “The green foxtail will compete more with the flax than with a crop that’s rooting at a different level.”