Addressing objections and providing solutions for maintaining soil health when growing potatoes
Potatoes can be one of the hardest crops on your soil. Deep tillage, hill formation, and heavy equipment all take their toll. In this article, I’m going go through some of the common hurdles and potential solutions to building or maintaining soil health in the year that potatoes are grown. In a companion article, I’ll present specific ways to work on soil health in the rotational years leading up to potatoes.
Let’s get the big one out of the way to begin with – tillage. There’s no doubt about it; potatoes disturb the soil. You could auger a very small hole and drop the seed piece, but you’d still need to dig out the tubers. Think about the tubers as they grow. A plant that produces 1.5kg of tubers displaces the same amount of soil as ten tennis balls!
When talking about building soil, remember that we are applying principles. This means that you don’t need to follow them all to get a benefit. Each works at a particular area of the system, and the integration of them all determines the soil’s health. You can’t no-till in the year of the potato, but you can still no-till or minimize tillage in all other parts of the rotation[i].
Recognize that you won’t get all of the benefits that long term no-tillers swear by, but don’t worry about it. I believe that a focus on the other principles can compensate for the effects of tillage. No-till gets the biology working in the top few centimeters of the soil, but living roots in the ground get the biology working 15cm or more into the soil.
There is evidence that tillage is not as bad as it was once thought to be. The harshest criticism of organic producers is that they rely on tillage more than their conventional neighbours. When the soil is studied, organic producers that incorporate the principles of soil health and work to reduce tillage can have soil that is just as healthy as conventional no-till[ii]. You can’t avoid tillage when growing potatoes, but you can make the soil resilient and able to handle the tillage.
Think about nature itself. Tillage is not avoided at all costs. Animals burrow into the soil and dig up insects to eat. In the area I live in, the western Canadian prairies, the grasslands were developed over thousands of years by the bison trampling the surface. Even healthy soil advocates talk about biological tillage. Earthworms move through the soil creating small tunnels throughout. Tillage radish is a long, thick root going deep into the soil. In the top 15cm it can leave a hole 5cm or more in diameter.
The second biggest objection to integrating the soil health principles into potato production is the integration of animals. This is tougher in a potato rotation, but not impossible. If you are set up to be able to graze your fields, then you may be able to add animals into one of the years between potatoes. If not, consider spreading manure or compost. Food safety protocols usually don’t allow manure application to potatoes in the year of production, and for a good reason. Fresh manure or even composted manure needs time to break down potential human and potato pathogens present. If you choose to add manure, I suggest after potato harvest. This gives lots of time for pathogen breakdown, and it gives a kickstart to regenerating the soil. It also gives a great chance to incorporate the manure. There will be tillage after potato harvest, so this is an excellent time to incorporate new material.
Now that the two toughest principles of soil health have been covered let's look at ways to apply the final three – keeping the soil covered at all times, increasing plant diversity, and planting cover crops.
Creating the hills leaves the soil uncovered and potentially exposed to wind and water erosion. Using plants for loosening the soil and building aggregates in the rotational years may mean being able to form the hills with less tillage in advance. Even though the hills may be sitting uncovered, greater aggregate stability and some residue incorporation into them may hold them better.
If the hills are marked out in the fall prior to planting a potato crop, a quick-growing cover crop could help bind the soil with roots and provide some cover to the surface. However, the cover crop could cause problems at planting, even if it has winterkilled. Powerhilling may be able to incorporate and break up the residue, but it also breaks up aggregates and can lead to a more erodable soil.
After the crop is planted and the rows are hilled there is a long period until the plants emerge and begin to cover the soil. In a study by John M. Jemison Jr,[iii] they were able to establish a cover crop after planting but before hilling with no detrimental effect. It may even help with insect control by encouraging the beneficials to establish in your field before pest invasions[iv].
What would happen if this cover crop could be established immediately after planting? A hiller that broadcasts a quick-growing cover could follow the planter. The potatoes don’t usually crack through the surface for at least three weeks. Even if there doesn’t appear to be much above ground growth, there would be roots in the hill holding the soil in place. At herbicide timing, this cover would be killed, but then it would leave the soil armor that potato fields desperately lack. It’s possible that this mat of residue would help to regulate the temperature of the hill, decreasing the chances of sugar end development. The cover also may help in early season irrigations by helping to channel the water into the hill rather than running off and into the furrow.
After harvest, the soil is at its least healthy state. It’s been tilled with multiple machinery passes that formed, planted, hilled and finally dug up the potatoes. Not only that, trucks used for hauling the potatoes off the field compact the soil. Harvest can be the most compacting time with nearly every square centimeter tracked with diggers and trucks. In addition, consider that the crop has just finished growing and so has depleted many of the nutrient reserves in the soil.
One quick fix to covering the soil is to spread straw right after digging. This can work well, but it has its limitations. The straw is not anchored into the soil and can still be blown around.
Another way to deal with the lack of soil cover after potato harvest is to spread a cover crop prior to digging. As the potatoes are dug, the cover crop is planted. This can work well, but the cover can be patchy. Where the seeds go too deep, there may not be much growth and where heavy wheel traffic has compacted the soil nothing may come through. Alternatively, a cover can be spread and tilled in or just directly planted with or without prior tillage to smooth the surface. In all cases, there is still a lag where there is uncovered soil. Depending on how late it is in the fall, it could be two weeks or more until something comes up.
It seems impossible to establish a cover crop so that there is no gap in soil cover after the potatoes have been dug but its time to apply some new thinking. Corn farmers thought that it was too late to plant cover crops after corn harvest. Corn is harvested late into the fall, sometimes bordering on when the snow flys. It seemed impossible to have a cover crop, but then farmers and researchers experimented with planting a cover crop between the rows just before the corn crop fills in[v]. The cover crop starts to grow but doesn’t do much as it is shaded by the canopy of the corn. As long as it’s a low growing plant (that doesn’t climb the stalks!), it won’t interfere with harvest, and the soil is already green once the combine has gone over.
Can a similar system be developed in potatoes? Diggers have been developed that only dig the row and leave the space in between untouched. If a cover crop were planted between the rows when the potatoes are 20-30cm tall, the potatoes would have the rows covered within 2-3 weeks. The cover crop would sit underneath the canopy not doing much until the vines start dying down. I recognize that vine killing with desiccants could pose a problem, and this would need to be solved. If the other benefits of the system can be proven, then we can work at ways to kill the vines without killing the cover crop. It might even be possible to seed the cover crop between the rows at vine killing and then have 2-3 weeks before digging to allow the cover crop to establish.
Imagine then, having a cover established that could be driven over and left in place. After harvest, there would be green strips through the field. This wouldn’t give full protection, but it would be better than no protection. A quick growing cover could still be spread in advance of digging or right after to fill in the dug up areas. Having plants growing in the furrows may aid harvest by drying down these areas and giving grip to the tires. A fall rain that soaks the ground may not hold up harvest as long with a cover between the rows as it would when there is nothing.
In this article, I’ve covered how to integrate soil health principles into potato production in the year that the potatoes are grown. Most of the ideas that I’ve presented are going to require designing new equipment and a new system for digging potatoes. The potential benefits are to hold the soil in place and have a firm surface for digging, even in adverse conditions. In a companion article, I’ll explore the ways soil health can be integrated into the rotational years.
Are you in need of help to build soil health while growing potatoes? Please feel free to reach out today with any questions, requests, or concerns. I can be reached at: email@example.com
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Sources & Further Reading
[ii] Joel Gruver & Michelle Wander . 2018. Use of Tillage in Organic Farming Systems: The Basics
[iii] John M. Jemison Jr. 2018. Use of Nurse Crops in Potato Production to Protect Soils from Erosion.