Fertility and Nutrients

One of the more than 70 USDA studies in Maine looking at the effects of crops like mustard, rapeseed and barley in potato rotations. Photo by USDA-ARS

If you’re dealing with some tough soil-borne diseases, adding canola, mustard or rapeseed to your potato rotation could help.

That important finding emerged from recent potato rotation studies in Maine, led by Dr. Bob Larkin, a research plant pathologist with the United States Department of Agriculture (USDA).

Over the last 12 years or so, the USDA researchers have conducted more than 70 trials to investigate the effects of different rotations on soil-borne diseases in potatoes and on potato yields. Although the results varied from year to year and field to field, overall, Larkin and his research team found that crops in the Brassicaceae family, such as canola, rapeseed and mustard, consistently reduced potato diseases like black scurf, common scab and Verticillium wilt, and significantly improved potato yields.

Now researchers in Atlantic Canada will be examining the effects of Brassica crops as part of a major potato rotation project.

Three-pronged attack
Larkin explains there are three general mechanisms by which rotation crops may reduce soil-borne diseases – and Brassica crops likely act in all three ways.

“The first mechanism is that the rotation crop serves as a break in the host-pathogen cycle,” he says. “This mechanism is in effect any time you have a rotation crop that does not have the same pathogens as your host crop. This is a general strategy of increasing rotation length by adding other types of crops. The longer the time between your host crop, the more its pathogen population declines.”

“The second mechanism is where the rotation crop causes physical, chemical or biological changes in the soil environment,” Larkin says. “It may stimulate microbial activity and diversity, it may increase beneficial organisms, and things like that, which then help compete with pathogens and reduce pathogen populations.” This mechanism varies with different rotation crops.

“The third mechanism is where the rotation crop has a direct inhibiting effect on either particular pathogens or general pathogens,” he says. The rotation crop may release suppressive or toxic compounds in its roots or residues, or it may release compounds that stimulate certain beneficial microbes that suppress pathogens. Only some crop species have this mechanism.

The first mechanism by itself may not be very effective for controlling some soil-borne pathogens that can survive for many years without a host plant.

Brassicas are well-known for the third mechanism. They contain compounds called glucosinolates, and when Brassica plant materials are incorporated into the soil, the glucosinolates break down to produce other compounds, called isothiocyanates. Isothiocyanates are biofumigants that are toxic to many soil fungi, especially fungal pathogens, weeds, nematodes and other pests.

Larkin’s research shows Brassica biofumigant activity is greatest when the crop is incorporated into the soil as a green manure. However, even when a Brassica crop is harvested and then the remaining crop residues are incorporated, there is still some biofumigant effect. The amount of the biofumigant effect also depends on the Brassica crop’s glucosinolate levels; canolas have relatively low levels, rapeseeds somewhat higher, and mustards have the highest.

“With any of those Brassicas, you will get some benefit from incorporating the crop residues. And it is a measurable and real effect on both potato yield and on reduction of potato diseases,” he notes.

As well, Larkin’s studies indicate Brassicas also provide the second mechanism.

Brassicas seem to have an ability to alter soil microbial communities in different ways which is not necessarily related to their amount of glucosinolates or their ability to act as a biofumigant. I think the aspect of how they change the soil microbiology is equally important to their biofumigant effect,” he says.

For example, the USDA researchers found that canola and rapeseed sometimes do a better job at reducing black scurf (Rhizoctonia solani) than some of the higher glucosinolate mustards, and the effect on black scurf works even without incorporating the Brassica crop.

However, Larkin’s studies also show that managing some other diseases – like powdery scab (Spongospora subterranean) and Verticillium wilt – requires a full green manure.

Two-year rotation is too short
If disease suppression is a major goal of your potato rotation, then Larkin’s research results provide some key factors to consider.

First, a Brassica’s disease suppression effect won’t last forever, so the potato crop should immediately follow the Brassica in the rotation to get the greatest benefit.

Second, a two-year rotation will not effectively reduce disease in the long run. Larkin found that no matter what crop was in a two-year rotation with potatoes, certain pathogens tended to build up over time.

For example, in one 10-year study the researchers compared two-year rotations in fields where common scab and Verticillium wilt were not problems at the beginning of the period. But by the end of the study, both diseases had become substantial problems in all of the two-year rotations. The canola-potato and rapeseed-potato rotations had significantly lower disease levels than the other rotations, but they still had gradually increasing amounts of common scab and Verticillium wilt.

“So we recommend a three-year rotation as your first line of defence, and then including a disease-suppressive rotation crop in one of the years of that three-year rotation,” Larkin says.

A Brassica green manure could be a good choice for the disease-suppressive crop, or you could grow a Brassica as a full-season crop and follow it with a disease-suppressive cover crop. “The addition of a cover crop like winter rye or ryegrass, in combination with your Brassica, can provide a significant addition to the disease reduction,” he notes.

Even though the grower would not be earning any direct income from a green manure or a cover crop, these options can be valuable tools to get serious soil-borne disease problems under control.

“That’s really how we first got into this research,” Larkin explains. “Some potato growers [in Maine] had some soils with substantial disease problems, and they wanted to try whatever they could to get those soils back to where their potatoes would be producing better. So they were willing to give up a seasonal crop for a year or two, to try to get the pathogen populations down to controllable levels.” (Two seasons of a green manure might be necessary if the field has very high pathogen populations.)

A third factor to consider is whether the rotation crops share any pathogens with potatoes. In Maine, the only shared pathogen that increased in potato-Brassica rotation trials was sclerotinia.

In his own studies, Larkin hasn’t had any sclerotinia issues because sclerotinia is not common in Maine potato fields. However, a researcher at the University of Maine found two fields with sclerotinia and did some rotational trials there. Sclerotinia increased in those two fields when canola or rapeseed was in a rotation with potatoes.

“So if you have a field with a history of sclerotinia problems, then a Brassica may not be the best rotation crop for you,” says Larkin. Alternatively, adding a cereal crop to a potato-Brassica rotation may help because cereals are not susceptible to sclerotinia.

Maritimes rotation project
The major potato rotation project now underway in Atlantic Canada is examining various crop options including canola and some other Brassicas.

Dr. Aaron Mills, a research scientist with Agriculture and Agri-Food Canada (AAFC) in P.E.I., is leading the project. He is conducting trials at AAFC’s Harrington Research Farm in the province, involving nine different three-year rotations.

The project is funded under Growing Forward 2, with support from AAFC and the Eastern Canada Oilseeds Development Alliance Inc. McCain Fertilizer division is collaborating by conducting a similar study in New Brunswick.

Generally, the project’s three-year rotations involve a year of potatoes, a year of another high-value crop, and a year of a more diverse crop mix or a biofumigant crop. “We’re looking at canola, soybean and corn [as the high-value crops], and at other, more diversified phases in the rotation, including blends of a Brassica, a grass and a legume all planted at the same time,” Mills explains.

He notes, “The canola acreage is increasing slightly in Prince Edward Island, it is one of the higher-value oilseed crops, and it does very well under our climate. And it’s important to diversify the cropping system, so if you can add in a different crop and it’s a higher value crop, then that’s a win-win situation.

“Canola has also been touted to have some biofumigatory effects, and the Brassicas in general produce certain compounds shown to have effects on diseases and insect pests,” Mills says. “Buckwheat is another [crop that supresses pests], based on research by my colleague Dr. Christine Noronha, so we’re also including buckwheat in the trials.”

Mills and his research team will be scouting all the crops in the different rotations for disease and insect pests. Sclerotinia is one of the issues they’ll particularly watch for. Mills notes, “We are starting to see an increase in sclerotinia [in P.E.I.], and a lot of the higher value crops in these rotations are hosts for sclerotinia.”

Along with collecting data on crop yields, diseases and insect pest issues, the researchers will also be monitoring such factors as crop biomass and soil organisms including nematodes. And Dr. Judith Nyiraneza, an AAFC nutrient management specialist, will be tracking nutrient dynamics in the soil.

The researchers conducted preliminary work in 2013, and 2014 was the project’s first full year. The current funding will take the project to 2017-18, but Mills hopes to run it for nine to 12 years. “You can’t really look at the trends until you get at least a couple of phases of each rotation. So one of the big determinants for the project’s success is how long we can run the rotations,” he says.  

Putting it all together
The effects of different rotation crops on potato diseases and yields may differ somewhat from region to region. Mills emphasizes the importance of evaluating rotations in different regions: “P.E.I. soils are different than those in Ontario or out west, and how the crops respond is not exactly the same.”

Mills’ overall advice for effective potato rotations is that more diversity is better. “From what we’ve seen so far with some of our other studies, it’s all about increasing the crop diversity. You can increase the length of the rotation by adding different crops. Or, if you have a shorter rotation, you can increase [the in-year diversity]. That seems to show some benefits to the soil and to the organic matter especially,” he says.   

Similarly, Larkin advises using multiple rotation-related practices for enhanced disease suppression. Examples include: increasing the rotation’s length, adding crops that also have the second and third mechanisms of disease suppression, and including cover crops and green manures.

His research shows that, although these practices will not completely eliminate potato diseases, they will reduce soil-borne potato diseases and improve potato yields.

As well, these kinds of sustainable practices provide other long-term benefits for a farm’s production capacity and potential longevity. These benefits include improving overall soil health, enhancing soil microbial diversity and activity, increasing soil organic matter and building a healthier agro-ecosystem. “All these practices are components of making a better, more sustainable system,” Larkin says.

For potato growers in Maine, Larkin’s general rotation recommendation is “a three-year rotation, with one year of a grain such as barley, then a cover crop like ryegrass or winter rye, then a Brassica, which could be a mustard green manure or a harvestable oilseed Brassica crop, and then potato in the third year of the rotation.”

He notes, “That recommendation is based on a lot of different studies looking at what is the best system for reducing disease, what is the best system for improving soil quality. Now [in our current studies] we are trying to combine those into a rotation that incorporates aspects of all of those things and seeing if it really does everything we hoped it would.”

 

Sept. 25, 2014, Prince Edward Island – A new method of applying fertilizer to potato crops, with the intent to grow a more desirable potato while cutting down on costly fertilizer waste, is showing promise in Prince Edward Island, reports The Guardian. | READ MORE

Southern Alberta is well known as cattle country, but the region also is home to significant commercial potato production. Now, a partnership between a potato grower and cattle producer has proven to be a fortuitous – albeit rather unorthodox – opportunity to unite the two industries for mutual benefit.

Harold and Chris Perry are co-owners of the Kasko Cattle Company, with feedlot owner Ryan Kasko, on 10 quarter-sections of land surrounding the Kasko Cattle Company feedlot east of Taber, Alta. Kasko owns and operates the feedlot itself, which raises about 14,000 head of cattle annually. Harold Perry says they partnered with Kasko in the recent purchase of the land surrounding the feedlot partially because it provided them with a ready supply of manure that they could convert to compost for use in their potato production.

The potato producer benefits primarily from the nutrient and micronutrient value delivered by the feedlot’s manure when it is applied on potato cropland in the form of compost, while the feedlot has a handy place to dispose of its significant accumulation of manure right nearby. The feedlot owner delivers the raw manure to a dedicated composting site with good drainage control where the potato producer converts it to compost. It is land applied in October and worked in before the potato hills are created for next year’s planting.

The Perry family’s expertise, which includes Harold and Chris’ father, Gerald, is in producing crops such as potatoes, sunflowers and peas on a total of 4,600 owned and rented acres. Their business is headquartered close to the town of Chin, about 40 kilometres from the feedlot – a typically hot, dry climate requiring irrigation, with plenty of frost-free days. The Perrys have a contract to produce 13,500 tonnes of potatoes for Frito Lay and 8,500 tonnes of potatoes for McCain Foods on about 1,300 acres that are under irrigation for that purpose.

For the past decade, the Perrys have used cattle manure compost as fertilizer in their potato-growing operation because of the nutrient and microbial benefits they’ve realized from using it. Harold Perry says they observed with growing potatoes on virgin potato growing soil versus soil that had been under cultivation previously in a four-year potato crop rotation that there was a dropoff in potato production on soil where potatoes had been grown in the past. They discovered that using compost on the potato rotation land not only provided organic fertilizer to the crop but also worked as an excellent soil amendment, adding many micronutrient and biological unknowns to the overall quality of potato-growing land that really made a difference in commercial potato production.

“We wanted to try compost because that is the natural way that things work,” says Perry. “When the buffalo were here, they ate and manured the grass at the same time, and that’s how the natural cycle worked. Fertilizer prices have also helped because compost makes sense if you go strictly by dollars. The cost of putting the amount of nutrients you put on your soil using compost is less than if you were to purchase that at a fertilizer dealership.”

Composting the manure deals with that issue, and it is also more economical to transport nutrients in this form than as raw manure. The Perrys can attest to that fact.

“Good compost has about 60 per cent of the weight of raw manure,” says Perry. “So if you get too far away from the feedlot, then the trucking just kills you.”

Research being conducted by Agriculture and Agri-Food Canada, specifically in Summerland, B.C., also is showing that the addition of compost could help in the prevention of verticillium wilt, also known as early dying syndrome.

Potato crops infected with this pathogen will typically see the tops of potato plants die off between early August and September, which can have a devastating impact on potato production in the case of a bad outbreak. The pathogen enters the plant through root lesions. The root lesions are caused by nematodes that live in the soil and feed on the roots.

So far, what the B.C. research has shown is that the addition of compost enhances the presence of a fungus that feeds on the nematodes, thus reducing the amount of root lesions and closing the pathway for the verticillium wilt pathogen to enter the plant. Results so far have been promising, although the theory hasn’t quite been proven yet, according to Dr. Frank Larney, research scientist in the area of soil conservation with Agriculture and Agri-Food Canada (AAFC) at the Lethbridge Research Centre in Alberta.

Before the Perrys became partners in the feedlot, they were purchasing their compost from a commercial supplier. It was partially because of compost quality issues that they agreed to invest in land surrounding the Taber area feedlot with Ryan Kasko so they could acquire their own supply of raw cattle manure to manufacture compost. The Taber feedlot and surrounding land were also near their potato growing operations, so all the pieces conveniently fell into place.

Harold Perry is in charge of compost production. “If I have a goal, it’s to have healthier soils, for healthier crops, for a healthier population,” he says.

The Perrys pay Kasko for the cattle manure, and he in turn hires a custom contractor to deliver the raw manure to the compost production site. The custom manure hauler creates the windrows needed to produce compost. During the first year of compost production, the feedlot delivered about 9,000 tonnes of manure to the site. Delivery of the manure resulted in four windrows measuring a distance of about half a kilometre each.

Once the windrows were created, Perry began monitoring the conversion process and used his compost-turning equipment as needed. He acknowledges feeling a bit anxious about delving into compost production because of the science required to ensure that the biological organisms have a healthy environment to carry out the conversion process but adds that learning to compost has been an enjoyable experience. To prepare himself, he took a composting course offered by Midwest BioSystems. The conversion process takes from July to mid-October.

To turn the compost, Perry purchased a 14-foot wide, pull-type, Sittler compost turner, which retails for about $45,000. He was able to recoup about half the cost by applying to a government program called the Growing Forward Manure Management Program. He checked the heat and moisture content in the composting windrows regularly to ensure that the organisms were working in an optimum environment. He also purchased a Sittler water wagon that can be towed along with the compost turner so that moisture can be applied to the windrows as needed. Perry says he turned the compost six or seven times with the main determining factor being when the temperature in the compost heap reached 160 F. At the beginning, the turning was done every four or five days because of the strong biological activity underway. Ideally, the conversion process should take 10 weeks, but Perry says he prefers to wait 16 to 20 weeks.

As part of the Perrys’ adventure into composting, they hired an agriculture consultant from Sunrise Ag in Taber to soil sample and develop topography maps to help determine how much compost should be applied at various points on their cropland. The consultant developed maps showing six zones where the compost should be applied to a lesser or greater extent to achieve ideal growing potential.

To spread the compost, Perry purchased a Bunning compost spreader with vertical beaters, which he pulls using a John Deere 8430 tractor equipped with hydrostatic drive. Perry recommends a tractor in the 180- to 200-horsepower range. The tractor moves at about 16 kilometres per hour, and the spreader broadcasts the compost over a width of about 40 feet. This results in an application rate of about four tonnes per acre. Increasing or decreasing tractor speed based upon the zone mapping displayed in the cab will increase or decrease the application rate.

Larney says he is not surprised by the results witnessed by the Perrys. He says using compost in the lighter, sandier soils under irrigation in southern Alberta delivers “a better bang for your buck” than perhaps it would in the soils where seed potatoes are grown in central Alberta. These soils typically contain more organic material. Given the amount of row crop type production in southern Alberta and because these crops do not return organic matter to the soil, Larney says, “the addition of compost is a very good way of replenishing soil organic matter . . . it’s the quickest way.”

He adds that compost also delivers other benefits, such as the addition of micronutrients not present in commercial fertilizer, and also improves the soil’s water holding capacity, making it more resilient to both wind and water erosion.

Given how close together both cattle and potato production are in southern Alberta, he says their co-operation is a natural fit.

“It kind of makes sense that it (manure) should end up on potato land,” says Larney. He is noticing more feedlot operators moving in the direction of composting the manure in advance versus simply land applying raw manure.

“I think a lot of feedlots are now realizing that they should look at composting because you can only rely on your neighbours for so long to take raw manure,” he says. “With the buildup of phosphorus levels in particular close to feedlots, I think the onus is on the feedlot owners to hopefully ensure that these nutrients are spread out over a wider area so that we are not getting high nutrient loading on land close to the feedlot.”

Potato crops require large amounts of most inputs and potato growers seek economical alternatives for what this high-value crop requires.
One day soon, you might be able to give your potato crop an extra boost from beneficial bacteria, thanks to some innovative studies by Ontario researchers.
Adjusting fertility programs by the tiniest increment could net a yield increase. All that might be required is better understanding the soil’s needs or choosing nutrient materials that will work more effectively in particular soil profiles. Three top potato experts share their tips for tweaking fertility that are valid for any potato operation. While most of the recommendations are not new, they may be getting overlooked or they may need to be combined with others in order to get better results.
A simple blood test at a medical laboratory can tell your doctor a lot about your health. From the test results, a doctor can suggest ways to improve your overall well-being. Human blood tests were the inspiration for Agriculture and Agri-Food Canada (AAFC) researcher Dr. Helen Tai to consider a test for nitrogen levels in potatoes. She wondered if a test could be developed that would tell potato growers if the amount of nitrogen in their plants is in the right range for a “healthy” plant. She took the idea to Dr. Bernie Zebarth, a soil scientist at AAFC, and the two Fredericton researchers began a collaboration that has resulted in a test. Now, they just have to make it accessible for plant “doctors.”

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