It's just a big pile of ground rocks. But a taconite tailings basin is a good place to grow alfalfa when biosolids from a municipal waste treatment facility are added, says Jim Takala.
Takala, of Iron, MN, has 180 acres of the crop on the flat top of a 150'-high tailings basin seven miles from his dairy farm. In this, the first production year, he expects to harvest about 4 tons/acre from three cuttings, despite an early summer dry spell. That's about the same yield he'll get from his other alfalfa fields.
“It's doing quite well,” he says.
He's finding out if alfalfa can be grown economically on the 500-acre basin, which is next to United Taconite's iron ore processing plant. The Western Lake Superior Sanitary District, Duluth, MN, spreads the biosolids, and University of Minnesota Extension of St. Louis County provides technical help.
County extension educator Kendall Dykhuis says it's the first time a crop has been grown on taconite tailings, which are an iron ore byproduct. There are six tailings basins on Minnesota's Iron Range, and none of the others are used for agricultural purposes, says Dykhuis.
Two years ago, Takala needed more feed as he expanded his herd from 80 to 220 cows and brought his son, John, into the operation. The sanitary district was already spreading biosolids on tailings basins for vegetative reclamation. Dykhuis had seen alfalfa growing at a reclaimed mine and thought it might do well on a tailings basin, too. United Taconite's parent company, Cliffs Natural Resources, agreed to participate, so Dykhuis brought the parties together.
He credits Takala for his willingness to try something new and mining company officials for their cooperation. “Their environmental department has been excellent to work with,” says Dykhuis.
In spring 2008, Takala seeded the alfalfa plus 300 acres of bromegrass, and Dykhuis established a 20-acre trial plot with switchgrass and other potential biomass crops. Tailings vary in size across the basin, so the dairyman put the alfalfa where the particles are fine, figuring that area would have the highest water-holding capacity. He planted an oats cover crop to control dust until the alfalfa established a ground cover.
No commercial fertilizer was applied, but 17 tons/acre of biosolids were spread the previous winter. Dykhuis says the tailings are suited for alfalfa production because they're high in potassium and calcium sulfate, and their pH ranges from 8.2 to 8.7. But they need the organic matter, phosphorus and nitrogen from the biosolids.
Concerned that the tailings' high pH might inhibit micronutrient absorption, Dykhuis had plant tissue samples analyzed both years.
“Everything's in the sufficient or high range except boron,” he reports. “The boron uptake is in the low range, but the alfalfa is not showing any symptoms of boron deficiency. There have been no problems with uptakes of any of the other minerals.”
This year's first cutting, harvested as baleage, tested 20% protein with a 150 relative feed value score. It yielded 1.7 tons of dry hay equivalent per acre, and the second cutting added 0.83 ton/acre. If rainfall is sufficient for a good third cutting, the season-long yield will be close to 4 tons/acre.
But the economics are iffy. Takala pays the mining company in the form of 200 tons/year of bromegrass mulch hay that he harvests on the basin. This year he's also being charged for the nitrogen in the biosolids in addition to paying to have them trucked about 50 miles, and it costs him roughly $13/ton to haul the round alfalfa bales home.
“We'll have to see if the cost structure works out with the additional charges for the biosolids,” says Takala. “We'll analyze it at the end of the year.”