Do not Poop on My Potato

Idaho spud seeing its fair share of dairy manure runs
By Gregory Jackson, Founder of Groundz recycling organization

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Marie Antoinette liked to wear potato flowers in her hair, while her husband Louis XVI fastened potato blossoms in his buttonhole, French aristocracy fashion at the time. It is the meat and potatoes of our diet. Most of us eat potatoes in the form of French fries, potato chips, baked potato, and mashed. Most likely a baked potato will be smothered in cheese. While we may eat a couple varieties of potato the International Potato Center in Peru has saved 5,000 varieties.

All sorts of colors, Maine Potato Lady and Seed Savers Exchange, which offer all open-pollinated seed sources (technically potatoes are grown from tubers, a modified stem tissue), are planted in late March.

Potato likes well drained, sandy loam acidic soil, moderate in organic matter. According to James D. Utzinger, from Ohio State University Extension (1983), if your soil is heavy clay you will have to plant cover crops (like rye, wheat, or legumes) planted in the previous fall, and tilled under before the cover plant reaches 12 inches, tilled 8-10 inches deep, and wait a week.

Joe Eck and Wayne Winterrowd, founding farmers of North Hill Farm in Vermont and Utzinger warn the use of manure-based compost for growing potato. Eck and Winterrowd agree that manure-based compost, no matter how old in the composting process, cause potato to scab.

Amber Moore and Nora Olsen from Idaho State Extension, presented “Manure Management and Potato Production” for Russet Burbank potato at the Idaho Potato Conference on January 20, 2010. Recent growth of the dairy industry expanding into prime Idaho potato fields of extensive and recent manure applications, have led to the increase in the use of manure for potato crop.

They found that soil nitrate, potassium, calcium, magnesium, sodium, and phosphorous had significant increase in the soil in the first year. Further, the nitrogen from manure compost affects potato yield as compared to adjusting phosphorous and potassium fertilizers.

Moore and Olsen also found that potato scabbing was likely with the application of lime and liquid dairy manure on acidic soils (increasing from 0.3 percent to 63 percent), but reducing soil pH reduces scabbing likelihood. Manganese becomes toxic to potato crops if pH is lower than 4.8; accumulation of potassium lowers starch content of the potato. At an organic-certified field in Kimberly, Idaho, Russet Burbank potatoes were given 8.9 wet tons per acre, at 6 inches deep in the spring, of fresh dairy manure that followed an autumn cover crop of barley tilled that same spring. Potato yield increased by 37 cwt/acre (or 3,700 pounds/acre) without scabbing.

Another consideration when growing potato with manure runs the risk of antibiotics accumulated in the crop, according to “Livestock Antibiotics Can End Up in Human Foods” a study in 2007 by the University of Minnesota. Other crops mentioned in the study especially sensitive to antibiotic accumulation in foods are corn and lettuce.

Since dairy farming has expanded in Idaho, spud farmers will have to consider manure-based compost in a larger soil organic mix. Growing potato should also include other organic materials like food waste and post-harvest waste (like dead plants, which provide excellent soil conditions for the production of siderophores to help plants uptake iron). If you want to grow potatoes in your own yard, never use manure-based compost. Plant a cover crop first, and then incorporate food/yard waste-based finished compost. Provide “Hilling” for the potato with soil when plants are 6-8 inches tall until ready for harvest at 15-18 inches (giving you a total mound around the potato at 5-inches at time of harvest) to prevent tubers from greening.

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