The eroded knolls or hilltops common in Prairie farmland are typically the least productive, often yielding considerably less than other parts of a field.
Curtis Cavers, an agronomist with Agriculture and Agri-Food Canada based at Portage la Prairie, Man., says there are ways to boost crop productivity in these problem areas.
Cavers provided an assessment of several practices that can help, in a presentation he delivered at the Manitoba Agronomists’ Conference held in Winnipeg in December and later in an interview with Grainews.
More Fertilizer
One obvious solution is to apply more fertilizer. Cavers says it’s one of the more effective short-term fixes for restoring productivity on eroded knolls. He notes it’s also relatively quick and easy for farmers to do, as it doesn’t require a big change in management practices.
The biggest drawback, however, is cost. Because fertilizer is expensive, Cavers says, “you want to make that as much of an informed decision as possible before you go and spend a lot of money on something like that.”
Cavers recommends testing the soil to see if additional fertilization will be effective. Farmers need to be aware that for some badly eroded soils —sandier soils or those with very little soil organic matter, for example — no amount of fertilizer is likely to restore its original productivity, he says.
In some instances, farmers may opt to not apply any fertilizer at all on eroded knolls, as a way to minimize their losses. However, he says, this can make it more difficult to improve these areas later, if that’s something they decide to do.
“If you are purposely shorting these areas for some nutrients, it’s going to be really hard to get a stand reestablished there.”
Farmers may also consider applying livestock manure to improve eroded hilltop areas; Cavers says solid manure especially is an excellent source of organic matter.
Some potential drawbacks include the risk of over-application and odours associated with livestock manure. He says the practice also requires patience, since it take time for the benefits of manure applications to be fully realized.
More Seed
Because eroded knolls tend to be inhospitable for crops, it can be tough to get a good stand established in those areas after seeding, especially in dry conditions. Cavers says one possible solution for farmers is to crank up their seeding rates.
As Cavers points out, larger plant stands are more competitive against weeds, and they also help to reduce evaporation and store more moisture in the soil. The crop residues left behind at harvest also act to increase organic carbon in parts of the field where it’s needed most.
“Say you double your seeding rate in some of these cases, there’s a chance you’ll get a better stand in an area where more plants are needed to do that,” Cavers says.
When soils are really poor, however, increasing seeding rates may not make much difference.
“It’s going to be very site-specific from place to place, even from one hilltop to another in the same field. Some places are going to be more severe than others.”
Cavers notes cost is another consideration for farmers. “For less expensive seed, this might be attractive as a short-term fix. For some expensive seeds like canola, it may not be quite as appealing,” he says.
More Water
Another fix Cavers cites is to supply more water to eroded knolls through irrigation.
“This can overcome a slew of limitations and setbacks, even in soils we would probably classify as not being particularly healthy,” he says. “If they’re kept moist and there’s a reasonable supply of water, they can produce crops better than one would expect.”
Cavers sees this as a more feasible solution for farmers who already have irrigated cropping systems in place than for those who don’t.
A big reason for that is cost. As Cavers points out, irrigation systems cost a great deal to install, and there are other considerations such as water availability and getting the necessary regulatory approvals. Also, not all farmland is suitable for irrigation.
“With some steeply sloping land or land that doesn’t hold a lot of moisture, now you’ve got to watch out for risks like salinization and runoff.
“Like a lot of things, we can recommend practices to make things better, but the devil is in the details. If you’re not careful, things could be made worse if you don’t check all of the possible outcomes.”
Redistribute Crop Residues
Cavers notes crop residues can be an important source of nutrients and organic matter and can also help to reduce evaporation and runoff and conserve moisture in fields. Redistributing these residues so there’s more of this material on eroded hilltops is another way to increase productivity in these areas.
Because crop residues are a readily available resource, this can be something relatively quick and easy for farmers to do if they have the right equipment.
He notes one method would be baling straw from lower parts of a field and transporting it to hilltop areas, where the material could be broken up and moved around. Cavers cautions, though, that putting down too much straw at the wrong time could do more harm than good.
“If you add too much, you can quickly make a mess of the seed bed and have problems develop because of that.”
Cavers says he believes a better method could be to focus on redistributing chaff instead, using equipment such as a chaff collection unit attached to a combine.
“Not many people have those, so you may not want to invest in that until you see if this concept has traction in your situation. You might be better even just to play around a bit at the start with your harrows,” he says.
Grow Cover Crops
Most farmers are familiar with the many benefits of cover cropping for improving the quality of soil, reducing runoff and conserving moisture in problem areas.
If that area is an eroded hilltop, though, Cavers cautions cover crops on their own may not be the ideal solution for producers aiming to restore productivity.
These are usually the driest and most difficult parts of a field to try to get any crop established, he says, which means producers need to have realistic expectations around growing cover crops there.
Cavers says farmers shouldn’t expect to see a 100 per cent success rate with this practice, especially at first, and he maintains cover cropping is best used in combination with other methods for boosting productivity in eroded hilltop areas.
Move Topsoil
Cavers is a proponent of landscape restoration, which involves moving topsoil from the lowest areas of a field where it accumulates over time and placing it in the highest areas where it’s needed most.
“You’re taking it from a place that could probably stand to have it removed and not have a major long-term negative impact,” Cavers says, “and then you’re putting it up on the hilltops where we hope it would have the biggest and longest-term positive impact.”
Since 2020, Cavers has been conducting field trials at several Manitoba sites as part of his research into the effectiveness of landscape restoration. His current practice is to scrape off six to eight inches of topsoil from low areas and spread it around on topsoil-deprived areas higher up.
Taking too big of a cut out of the low areas might create an artificial pothole where water will pond, though, so farmers wanting to try this practice need to be mindful of that. They should also be aware it can take a year or two for soil biological activity to be restored and for productivity to return to normal in areas where topsoil is removed.
Cavers recommends transplanted topsoil be firmed up a bit once in place on eroded hilltops and that farmers then avoid doing tillage in the affected area.
“Try and do what you need to create a nice seed bed and give crops you’re going to plant up there as much opportunity for success as possible,” he says.
“If you’re practicing low disturbance no till or you’re very strategic in how you till once you move that topsoil up to the hilltops, hopefully it will stay there as long as possible.”
Cavers notes it’s important to ensure topsoil used for this purpose isn’t taken from saline areas, because salinity will make it even more difficult for crops to become established.
According to Cavers, restoring the landscape this way results in an immediate increase in soil organic matter, and it can be a one-time practice if it’s done right.
But he says farmers still need to have realistic expectations; in really dry years, for instance, there won’t necessarily be a positive yield response.
“Again, I want to temper people’s expectations. It’s not like you’ll do it once and now you’ve got the same or similar yields up on top than you do at the bottom,” Cavers says.
“The potential is there, but it might take a year or two of things settling and just getting everything lined up and doing what it’s supposed to do.”
Cavers says he sees landscape restoration as kind of a foundational practice for restoring the productivity of eroded hilltops and increasing field uniformity.
“You get the soils fixed as best you can first, and you can then overlay a conscious tillage practice going forward, whether that’s low disturbance no-till or very strategic tillage,” he says.
“Then you can layer one of the other practices on top of that. Whether it’s residue management or cover crops or being more strategic with your inputs, these are all things you can do to tweak the situation so that you’ve got a better chance of increasing productivity.”
