Potatoes and soil health

CN-MR-1-Potatoesby Tamara Scully

Soil health is increasingly being recognized as a key factor in plant health and yield, and is the key to successful non-chemical growing. When the soil structure is optimal and left intact, the soil microbial activity is thriving, and carbon is sequestered, the conditions are perfect for crop production. But what if you grow a crop that requires soil disturbances for planting and harvesting? How can soil health be optimized when the soil has to be disturbed?

“No crop can disturb the soil more than potatoes, except for maybe peanuts,” David Lamm, NRCS, Leader of the National Soil Health and Sustainability Team  said, as he introduced their conservation webinar, “Managing for Soil Health when Raising Potatoes – A Farmer’s Perspective.”

Although potato tubers do require soil disturbance when planting, and potatoes do need to be dug up for harvesting, growing potatoes and improving and promoting soil health are not mutually exclusive activities. In fact, a thriving potato crop and healthy soil go hand in hand at Rockey Farms.

No longer conventional

Brendon Rockey, of Rockey Farms, LLC, in San Luis Valley, CO, is a grower of specialty potatoes, with both field crop and certified seed potato production. The family farm has undergone some radical changes over the past 20 years, as the Rockey family has taken a close look at what wasn’t working on the farm, and opted to change things.

The result? It’s a system of farming which they call “biotic farming,” and it is based upon the philosophy of taking care of the soil.

Rockey said, no matter the crop, soil health is imperative, and “the fundamental principals are universal. The fundamentals are all going to be very similar.”

The issues that farmers of all types are concerned with are insects, weeds, and soil and foliar diseases. In conventional agriculture, a “very linear approach,” which is focused on applying a variety of herbicides, fungicides and pesticides to “try to kill the problem,” is standard, Rockey said.

Rockey Farms also used this approach, but realized that they were having increasing problems as a result of their “solutions.” If you go out and kill the problem, it works well initially, Rockey said. But ultimately, resistance builds, the effectiveness is decreased, and the natural living system which could have helped solve the problem has been decimated.

Eventually, they realized that they could “either be pro-biotic, or anti-biotic,” Rockey said. “We have the ability to wipe the slate clean and start again.”

So they did. They are now completely chemical-free, with less disease, insect and weed concerns. They have also increased soil fertility and structure, and decreased water usage. They are also harvesting potatoes of better quality than they did when farming conventionally.


Changing perspective

Rockey Farms consists of 500 acres, one-half of which are planted to potatoes each season. When not in potatoes, the land is in a cover crop. Their traditional rotation crop was barley. Today, it is a diverse mix of dozens of species of plants, co-mingled together is a buffet of food, to feed the soil as a green manure.

“We get the benefits of each of these species every single year,” Rockey said of the diversity of plants in his green manure mix. “Each of the green manure crops has a specific benefit,” and the plants collaborate, not compete.

After realizing good results from adding Sudan grass to his barley rotation, in an attempt to target nematode problems, Rockey began adding other crops, too. Buckwheat, oats, peas, turnips, radish and vetch were added to the mix, and “we were just absolutely hooked.”

Although they began slowly, implementing life-affirming, positive solutions as alternative solutions to typical problems, the nature of soil health meant that improving even one thing built upon itself to improve everything else, in an upward spiral. While it took them 20 years to implement all the soil-building strategies they now use in their biotic farming approach, growers can implement all these practices simultaneously for the quickest benefits.

Their biotic farming system approach considers: beneficial insects; soil structure; beneficial soil microbes; soil carbon; predatory insects; and the interaction of all these components. The results they’ve had using this approach include “huge changes in our soil-borne pathogens,” and “huge impact in our fertility,” Rockey said.


Problems with potatoes

Aphids are a serious insect pest problem on potatoes. Using the conventional approach of insecticides is detrimental to soil insects, and will ultimately negatively impact soil health, Rockey said. So they focused instead on bringing in predatory insects to control aphids, and on increasing foliar health, as healthy plants are less attractive to insects and diseases.

With a diverse insect population, aphids can not thrive. In order to support the multitude of predatory insects, a diverse flora is needed. The multi-species green manures, along with peas interplanted in the potato rows as a companion crop, provided the needed flowers. Rockey has now introduced a full flower mix, planted in strips in the potato field as well as in a perimeter planting, as a companion crop, to increase diversity.

Encouraging beneficial fungi on the potato is another way to deter aphids. The beneficial species of fungus are “very good at controlling diseases to begin with,” Rockey said. Using fungicide is self-defeating, as fungicides kill the beneficial fungi, too.

Parasitic nematodes are also a big concern. Rockey noted the worst infestations were being seen in areas where soil fumigants and soil fungicides had been used. The use of these products kills beneficial soil nematodes. Beneficial nematodes actually make up 90 percent of the nematode population in the soil.

Adding inorganic N-P-K fertilizers, which are water-soluble and leach out of the soils, can increase the salt concentration of the soils, and can be harmful to soil life with overuse. Frequent use of inorganic fertilizers can cause fertility issues.

Fertility imbalances cause weed issues, and the types of weeds in the field can give a good indication of what the soil is lacking. Weeds thrive in compacted water-logged soils, so increasing soil structure means less problematic weeds, and also less water usage. Increasing soil structure and fertility through organic products results in efficient water-use. Rockey Farms utilizes animal manure-based composts, as well as incorporating their green manure crops, and fish-based fertilizers.
In addition, his soil is much less compacted. And as he’s built soil structure by adding carbon, his irrigation pivots no longer get stuck in the field.

“Just” potatoes

The fact remains that potatoes — rather than a diversity of vegetables — are the only crop at Rockey Farms. Year after year, on a two-year rotation, the potatoes are planted in the same fields.

Aside from the potatoes, peas are planted every year, as a cover, manure and companion crop to the potatoes. They are in all fields, all the time. The two-year potato/diverse cover crop rotation — including peas in the mix at all times — has not depleted the soil or caused disease issues, however.

Rockey Farms may only be growing one primary crop, but they are doing so within a life-enhancing soil system, and making every effort to increase the soil structure and microbial life. It’s a choice between promoting, enhancing and nurturing life into the system, or being “anti-biotic” and preventing life, Rockey said. And anyone can make the choice to change.

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