Soil advocates want potato growers to bump soil management up their priority list.
Marla Riekman, soil management specialist with Manitoba Agriculture, pitched soil management principles to growers and agronomists at Carberry’s Canada-Manitoba Crop Diversification Centre potato tour Aug. 14.
The root crop, by its nature, involves disturbing soil, something that soil health advocates are quick to argue against in other crops, pointing to detrimental impacts on soil microbe activity, soil structure and increased risk of erosion.
Potato producers, however, have little choice but to dig under the surface, and any management plan must work around that reality.
“We talk a lot about tillage erosion and the fact that tillage itself moves soil around the field and we forget that tillage is also seeding. Something like potato harvesting is something we consider to be a form of tillage because it’s moving a whole lot of soil around,” Riekman said.
Tillage erosion has been of particular interest to researchers like the University of Manitoba’s David Lobb.
“Root crop harvesting, like potatoes, will cause as much tillage erosion as all other forms of tillage combined,” he told the Manitoba Co-operator in 2016.
Lobb has argued that tillage erosion from knolls and hilltops can cause significant yield loss, and that landscape restoration (scraping soil from low areas back to the top of the knolls), can be an immediate help to yield the next season. In a recent article, Lobb was cited as saying that profits from each quarter section restoration would break even with treatment costs in 3-1/2 years.
Above the soil, typical potato land does little to combat wind erosion risk, Riekman added.
Digging into a soil pit at Carberry’s CMCDC potato site, Riekman pointed to the light, fluffy layer created by the highly cultivated sandy topsoil.
That top layer will have little staying power against wind, she said, particularly as potatoes, like soybeans, leave little residue after harvest to anchor soil.
Minimizing fall risk
While soil disturbance in potatoes is inevitable, both Riekman and Manitoba Agriculture crop nutrition expert, John Heard, urged producers to consider cover crops after harvest to minimize the risk of blowing.
“You want some kind of cover to basically protect from the wind blowing across the soil, but also help to build and put that soil back together rather than just leaving it just kind of fluffy on the surface and not covered with a lot of crop residue,” Riekman said.
This year however, cover crops may have a difficult time getting out of the ground.
Many regions are going into the fall with drought-like conditions, and lack of soil moisture has producers questioning whether a cover crop can establish.
Heard says he has seen producers follow potatoes with fall rye in the past.
“Sometimes, like last year, they get stuck where, if it’s dry and cool in the fall, they get poor establishment,” he said. “That’s a bit of a dilemma.”
Heard called for potato growers to reduce additional tillage as much as possible, given another dry fall in the forecast.
Wind erosion made for dramatic pictures last year, when high winds and dry soils left topsoil blowing over highways, reducing visibility and leaving dirt drifts through the winter.
Riekman suggested that producers consider packers and harrow bars to smooth land this year, although heavy rollers, such as what would be used with soybeans, might crush soil aggregates and make dirt more prone to flow.
That option will be a field-to-field decision, she said, and may not be appropriate as a blanket recommendation.
Looking longer term
Growers may have more options to avoid erosion in the long term.
“What you want to do is think about, ‘Where am I doing my tillage in my rotation?’” Riekman said. “There have been people who have practised ‘no till’ for potatoes — it’s not a common thing, but it has been practised in Manitoba — where you would actually direct plant the potatoes and then you hill them and you harvest them, which does a lot of soil disruption, but in the years between your potato production in the rotation, then they would no till the rest of it.
“What you’re doing is you’re helping to build aggregates and hold moisture and do all of those things outside of the potato years to try and benefit the soil within the potato years,” she said.
Compaction is a separate concern, Riekman said, pointing to a harder “plow pan” layer beneath the light topsoil at CMCDC.
Caused by both traffic and tillage shovels “scraping” the soil at depth, Riekman says compacted sandy soils may actually be more densely packed than compacted clay loam, despite being lighter, because of its small particles.
“If you’re going to do something like subsoiling, you want to make sure that it’s dry enough to till and dry to depth, so you’re not just causing more smearing deep down,” she said. “On a sandier soil, like a potato soil, there’s less chance that it’s going to be really moist because they have an easier time draining water out anyway.”
The province also suggests growers cast an eye to their tires. Tires should be at their rated pressure or below to limit compaction risk and producers should be aware of heavy equipment such as grain carts in the field.
Riekman estimated that heavy axle load on wet soils can cause compaction three feet deep or lower, well out of reach for equipment.
Alfalfa may help break up that deep compaction, Riekman said, although producers may be reluctant to take a field out of rotation and that solution might be measured in years.
The province says compaction risk is lower this year, given the dry conditions, although Riekman noted that many fields are still compacted from previous wet years.