Successful potato growers know that even the best soils can produce inferior yields and quality if steps aren’t taken after harvest to prepare their fields for the following year, whether it’s being planted with potatoes or another crop in their rotation.
We asked the following experts to identify and discuss some of the best management practices they’d recommend for an effective post-harvest field care strategy: Yves Leclerc, McCain Foods director of agronomy for North America who’s based in Florenceville, N.B.; John Goff, a potato grower and co-owner of Corduroy Plains Farms Ltd. in Carman, Man.; and Doug Pryor, an agronomist and co-owner of Delta Ag Services based in Portage la Prairie, Man.
Planting Cover Crops
Leclerc, Goff and Pryor all agreed that when possible, planting cover crops after potatoes makes a great deal of sense, as it helps keep soil from being carried away by wind or water though the winter.
“One thing we need to promote as much as possible is cover crops after harvest. I know it’s not always possible to do that because we tend to harvest late, but whenever there’s an early harvest, [adding] a cover crop will help prevent soil erosion,” says Leclerc.
“If you can maintain your soil, especially in areas that are prone to water or wind erosion, that’s very critical.”
Pryor believes that planting a winter annual crop right after harvesting potatoes is essentially “a must” for growers who can manage it. “I’m a firm believer that every potato field should have a cover crop planted on it,” he says.
According to Pryor, this is particularly important in potato-growing areas like parts of Manitoba that have sandier soils, which are often more prone to soil erosion.
“Traditionally in our area in central Manitoba, we either look at winter wheat or fall rye. If you can get it in early enough, then we’ll seed winter wheat, and if it’s a little later than we’ll seed fall rye,” he says.
Goff says he’s “pretty much gone to 100 per cent cover cropping after our potato crop” because of the sandy soils on his farm.
“In our area, we have a lot of problems with sand blowing and losing our topsoil. We’ve found the most effective way to deal with that is to broadcast some fall rye right after we dig potatoes and then do a very light double disking just to knock down the potato hills. We then go and plant right into that the next year,” says Goff.
Cover crops can also add valuable organic material and associated nutrients to the soil, but on Goff’s farm, “it’s not so much to build up organic matter, it’s more about controlling soil erosion,” he says.
Another common soil-related headache for growers is compaction. Harvesting potatoes requires a lot of heavy equipment and massive machinery that can really tramp down the soil, particularly in parts of the field that are prone to compaction, such as wet spots and heavy traffic areas.
If you can maintain your soil, especially in areas that are prone to water or wind erosion, that’s very critical.
– Yves Leclerc
“Especially after potatoes, I think one of the biggest issues that we’ve got is compaction. It’s often something we don’t necessarily understand very well, but it’s huge,” says Leclerc.
“It creates some issues in the following year, and compaction is also additive with time. If you’re not able to remove that compaction, you’re creating issues with drainage, of course. With drainage problems come poor root growth and poor plant development and greater risk of diseases,” he adds.
Reducing compaction, Leclerc notes, is largely about traffic control. “At harvest, you should try to minimize as much as possible traffic that you create, make it as site-specific as possible, and then go back afterwards and remove that compaction,” he says.
Pryor endorses deep ripping as a way to break up compacted soil, even on potato farms with sandier soils. “People think with sandy soil water just goes through, but there are depression areas in sandy soils where water [collects]. These areas become severely compacted because of water laying and ponding, so there’s definitely a benefit to deep ripping sand as well,” he says.
Pryor believes post-harvest tillage is generally a good management practice for getting fields ready for the following year’s crop. “The most important step I would say is to improve the structure of the soil, to break up any compacted areas, to allow for good rooting of the crop in the future year,” he says.
“I recommend deep ripping in any field that’s going into potatoes. So if it’s going to be potatoes in 2016, I would be deep ripping it in the fall of 2015,” Pryor says.
“Growers can rip anywhere from 12 inches down to about 18 inches and it basically shatters any of the hard pan,” Pryor adds, noting that deep ripping can also help build a better seed bed has more tilth to it and enables better rooting of the plants. It also helps address the critical issue of soil erosion.
“You want to be able to change that internal structure of the soil in that top plough layer but still maintain cover in way that eliminates the risk of soil erosion,” he says, adding that the grower’s decision on which implement to use is often linked to how susceptible a field is to erosion.
“It depends on what the soil type is, what their experience is with soil erosion, and what they’re trying to accomplish,” Pryor says.
“There are implements out there that will rip down 18 to 20 inches and totally leave your stubble standing. There are other implements that have a little more surface action and will knock down some of the stubble, and then there are other ones that will blacken it up quite well,” he says.
Goff says he doesn’t do any deep disc tilling on his farm because “we don’t have any compaction issues [and] we don’t have any root penetration issues, so it doesn’t really make sense in our type of soil. We have found deep tilling delays getting on the soil in a wet spring before the frost is gone.”
Goff does work his fields in the fall before planting them with potatoes, however. “We always have wheat or canola prior to potatoes,” he says, and in these fields following harvest “we’ll rip it with a four inch shovel, just to kind of open the soil up.”
Right before planting the potatoes, Goff will condition wheat ground with a straight blade coulter. “We find that just chops up the residue and gives us a lot better soil contact for the seed piece,” he says.
“I have coultered it in the fall in the past to chop up the residue but I don’t find that it does quite as good a job. It works a lot better in the spring after the straw’s had a chance to rot a little bit through the winter.”
Leclerc says burning residual vines following harvest is something growers may want to consider if their potato crops have been particularly hard hit by disease or pests.
“I know that it can be a bit contentious, but [it can be useful] in some situations,” he says. “Here [in New Brunswick], for instance, we used to have a lot of corn borer issues, and one good measure to control the problem in the following years was to burn to vines. That could also be good for other types of pests and diseases as well.”
According to Goff and Pryor, vine burning isn’t a common practice on potato farms with sandy soils because any available organic material is needed to help sustain he soil.
“We do have a problem with baling vines after the potato crop,” Goff says, adding that he’s found that giving the field a light double disc following harvest helps address that. “That kind of cuts the vines up and keeps the wind from blowing and baling them up.”
Pryor says potato vines help hold the soil together and that reduces the risk of water or wind erosion. For this reason, he says, growers in his region will often perform a light discing of their potato fields in the fall to help push the residual vine cover back into the soil.