How to promote crop resilience and maximum productivity when conditions are less than ideal.
Moisture is the most universally challenging factor in potato production: there never seems to be the right amount at the right time.
“A potato has a bit of a Goldilocks complex when it comes to water,” said Amanda Crook, the lead agronomist for western North America for McCain Foods. “The potato is very symptomatic when it gets too much moisture and it’s very symptomatic when it gets too little.”
While Mother Nature holds ultimate control, there are ways growers can promote crop resilience and maximize productivity when conditions aren’t ideal. Spud Smart hosted an early summer roundtable webinar with three agronomy and production experts, including Crook, to dig into the pre-season and in-crop steps growers can make to support their potato crops.
Excess Moisture
Last fall, potato producers in Canada’s eastern growing regions were plagued by excessive rainfall that caused, among other issues, upwards of 30 per cent soft rot in some storages. As they know all too well, saturated soil stresses plants and dramatically increases the risk of disease.
“When the lenticels are impeded by saturated soil conditions, they try to increase their surface area for gas exchange. The problem is this is opening that tuber up to infections like soft rot,” Susan Ainsworth, agrologist and general manager of the Keystone Potato Producers Association, said in the webinar.
Soft rot isn’t the only disease risk from excess moisture. In-crop diseases of multiple kinds, from pythium, pink rot, white and grey mold, to powdery scab (which can vector mop-top virus) are all supported by high moisture.
Saturated soil can also bring hefty costs in soil health and productivity. On top of dramatically increasing soil compaction problems, excess water can push water soluble soil inputs like nitrogen or potassium out of reach in the soil profile or into waterways or, if nutrients are surface applied, allow them to volatilize away.
Equally problematic, crop protection products can be broken down when soil is too moist. Losing crop protection and nutrition decreases the crop’s total payable yield and storability, both by increasing disease rates and by encouraging over-early plant senescence.
What can producers do in excess moisture conditions? Crook recommended holding off on applying crop nutrition and crop protection products until the field is fit, recognizing applying into an over-wet field is essentially an expensive waste. Even more importantly, she said wet fields are a critical time to recognize the value of team support.
“The biggest factor to success in the case of too much moisture is to increase your communication efforts… whether it’s with the agronomist, the field rep or the scheduler,” says Crook. “We can assist in best management practice decisions and appropriately deliver your raw into the factory to help mitigate any on-farm challenges.”
Too Dry
Achieving prime payable yields in moisture deficient soil is also a challenge. Early season excess moisture can lead to sugar ends, which is a major quality factor impacting growers’ profitability.
Ainsworth recommended that producers stay on top of moisture needs during the tuber initiation stages, and maintain adequate levels while tubers are between dime and egg size when they are most susceptible to sugar ends.
“If they start to look pointy, you know that they have undergone some stress,” Ainsworth said. “The critical threshold for soil moisture to avoid this happening is staying above 65 per cent. If [moisture levels] are in that 55 to 65 range, you’re going to see problems. It really only takes a single stress event for this to occur.”
Excess dry followed by too much water while tubers develop makes the problem worse, not better.
“Any abrupt change in tuber growth rate is going to cause knobs. Usually if you have a tuber that has those misshapen or knobs on them, you’ll also have hollow heart. The conditions that contribute to this are when you have a lack of water, followed by an abundance of water,” said Ainsworth.
The most fortunate producers have access to adequate irrigation throughout the growing season. For those who can irrigate but are restricted in the total amount they can apply in a season, Ainsworth recommended: “Make sure to put it on up front [at tuber initiation] where it’s going to have the most impact on some of these quality issues.”
As it’s not possible to persuade a sunny sky to rain, managing drought requires longer-term thinking, primarily based on promoting soil’s water-holding capacity.
Soil’s Role in Moisture Management
Channels — from large macrochannels created by earthworms and plants with thick taproots, to tiny microchannels created by fine branching roots and smaller soil organisms — are essential for water infiltrating into the soil profile rather than running off.
“We should try as much as possible to minimize how much we till the soil going into the potato crop,” Cameron Ogilvie, a soil health educator with the Soil Health Institute, said. “I know there’s a lot of preparation that needs to happen, but the more you break down the good structure you’ve built up throughout your crop rotation, the less you’re going to see the benefit of that soil structure that you’ve worked so hard to achieve.”
He recommended this easy do-it-yourself test to check on soil’s structure.
“If you take a shovel full of soil from your field and you open it up like you would open a book, you want your soil to fracture randomly, kind of like chocolate cake. But when you open it up and you start seeing these horizontal fracture lines, that is a telltale sign of compaction. And one of the things that comes along with that is plant roots growing horizontally along that fracture, which isn’t ideal for plants to be able to access water.”
While some producers use tillage to try to break up compaction, doing so is a double-edged sword. (Check out this article to see the benefits of minimum tillage.)
“Often tillage creates a compacted layer just below wherever that implement was set because it removed a bunch of the soil structure. And then it leaves the soil that much more prone to compaction afterwards,” Ogilivie observed.
A much better solution to compaction, Ogilvie said, is getting more roots in the ground via cover crops and diverse crop rotations. Each plant has a unique root system architecture that builds soil structure in different ways: alfalfa, daikon radish and sunflower have strong taproots that power through soil to build deep macropores that allow water infiltration; rye, oat and millet have hair-like root systems that form smaller micropores that allow water storage. Promoting root growth and minimizing soil disturbance are two winning strategies for maximizing the soil’s resilience to too much or too little water.
Future Planning: What and Where to Plant
While producers can’t control the weather, they can implement some solutions long before the season begins. One part of that is potato variety selection.
McCain’s goal for 2030 is to replace most of the standard varieties with new varieties that aim to reduce required nitrogen inputs, improve water use efficiencies and improve yield. Some of the recommended potato varieties are shorter season, which will also offer opportunities for cover cropping and/or reduced overall water requirements.
“Some of the growers that have experience with these new varieties so far are reporting between five and ten per cent [improvement in yields and reduced irrigation],” Crook said.
Where growers plant can be as critical as what growers plant. When developing your crop rotation plan, prioritize the highest potential fields for potatoes.
“Whether that looks like selecting fields with higher organic matter or heavier soil texture to ensure that higher water holding capacity, a field that has high resilience to perform even in a drought year may be a winning approach to achieving both quality and yield,” Crook noted.
Thanks to McCain Foods for sponsoring Spud Smart’s summer production webinar, and to all three speakers for making time to share their knowledge! This article is just a small taste of a very in-depth and informative hour-long webinar. The entire webinar is available free for on-demand viewing at: https://spudsmart.com/new-moisture-management-webinar-now-available/.
