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Concentrations of zinc, copper, iron, and manganese (Zn, Cu, Fe, and Mn) are determined by combining a 10-gram scoop of air-dried of soil with 20 milliliters of DTPA (Diethylenetriamine-pentaacetic acid) extracting solution, and shaking for two hours. The sample is then filtered and the extract is analyzed via inductively coupled plasma optical emission spectrophotometer (ICP-OES). Results are reported as parts per million (ppm) of each metal in soil.