Manure used to restore mined lands

Nov 9, 2012

Cattle manure applied to soil disturbed and contaminated by mining operations can help revegetate the landscape, a two-year USDA study shows.

Research soil scientist Paul White of the Agricultural Research Service (ARS) Sugar Cane Research Unit in Houma, LA, participated on a team that studied whether adding the compost would provide the carbon needed to support healthy plant cover at damaged postmining sites where there is limited organic soil carbon.

From 1850 to 1950, the Tri-State Mining District of southwestern Missouri, southeastern Kansas and northeastern Oklahoma produced 50 percent of the U.S. zinc and 10 percent of the lead in the U.S. The last active mine in the district closed in 1970.

Those thousands of acres with little or no vegetation remain throughout the region. Lead-contaminated soils, large amounts of mine tailings and toxic smelter sites remain.

ARS researchers wanted to determine if the compost could reduce levels of zinc and lead that could contaminate runoff during heavy rain. ARS is USDA’s main intramural scientific research agency.

They amended soils with 20 to 120 tons of manure compost per acre on experimental plots from the mine sites and created a cover crop of switch grass on all the plots. Then they took soil samples from the sites five times.

Now soils in the high-compost plots have significant increases in phosphorus, carbon, nitrogen, pH and available water. Nitrification potential, enzyme activity and microbial biomass also increased. Nitrifying bacteria are especially sensitive to toxic conditions, White said.

The binding enhances vegetative cover that reduces soil erosion and runoff.

The compost also lowered zinc and lead availability by about 90 percent. Heavy metals in soils disrupt soil microbe activity by harming cell membranes and damaging proteins. Lead is linked to serious health conditions, and high levels of zinc can hurt aquatic fauna in surface waters.

Soil microbes release nutrients from organic soil matter, producing enzymes that convert organic phosphorus into an inorganic form that can be used by plants. Heavy metals tend to bind tightly to organic matter in composted material, limiting their solubility. – Mark Mendiola, WLJ correspondent