Extractable Trace Elements in the Soil Profile after Years of Biosolids Application

The U.S. Environmental Protection Agency (USEPA) and some state agencies regulate trace element additions to soil from land application of biosolids. We generally consider trace elements added in biosolids (sewage sludge) to accumulate in the soil surface without significant transport below the plow layer. We used 11 yr of field‐study information from biosolids addition to dryland hard red winter wheat (Triticum aestivum L. “Vona” or “TAM107”) to determine the distribution of NH4HCO3 diethylenetriaminepentaacetic acid (AB‐DTPA)‐extractable Cd, Cr, Cu, Mo, Ni, Pb, and Zn in 0 to 20 (plow layer), 20 to 60, 60 to 100, and 100 to 150 cm depth increments. This study is unique since it involves multiple biosolids application in a dryland summer fallow agroecosystem. We applied five or six applications of biosolids from the cities of Littleton and Englewood, CO, to Weld loam (a fine, montmorillonitic, mesic Aridic Paleustoll) or Platner loam (a fine, montmorillonitic, mesic Aridic Paleustoll) at four locations. This paper focuses on the 0 (control), the 56 or 67 kg of N ha−1 fertilizer rates, and the 6.7 and 26.8 dry Mg of biosolids ha−1 rates that we added every crop year. We observed significant (P < 0.10) accumulations of the trace elements in the plow layer of the biosolids‐amended soils. Only Zn showed consistent increases in extractable levels below the plow layer at all four sites. The biosolids Zn concentration (average of ∼1300 mg kg−1) was larger than any other trace element resulting in larger loading of this element.