COPPER ACCUMULATION IN SOIL FROM NON-IRRIGATED MAIZE AND SOYBEAN FIELDS FERTILIZED WITH LIQUID SWINE MANURE, CALLAWAY COUNTY, MISSOURI

The application of liquid manure to cropland as fertilizer is used to solve two problems, namely the disposal of animal waste generated at the ever-growing number of concentrated animal feeding operations (CAFOs) and the replenishment of micronutrients including heavy metals into annually harvested cropland. However, if the amount of manure required to supply essential macronutrients is high enough that micronutrient supply exceeds plant uptake, heavy metals may accumulate in the soil and adversely affect crop production or the food chain. Furthermore, groundwater and overland flow, wind-borne dust, and fertilizer overspray may lead to a greater accumulation of metals in the surrounding non-harvested land. Using EPA guidelines, soil from a liquid swine manure (LSM) fertilized agricultural field in north central Missouri, its surrounding grassland and tree barrier, and a non-agricultural control area ~2 km distance from the field were sampled and analyzed by atomic absorption spectroscopy to determine EDTA-extractable copper soil concentrations. This 25 acre field has clay rich soil typical of the northern Missouri glaciated plain region, and has been annually fertilized with LSM over a 20 year period while following a standard soybean-maize crop rotation. Measured concentration of copper in the control area is ~2.6 ppm while the field averaged ~5.2 ppm. The surrounding grassland yielded intermediate value of ~3.1 ppm consistent with the relative immobility of metals in soils with pH greater than 5.5 as well as the low hydraulic conductivity of the clay rich soil. Assuming a linear accumulation of Cu in the soil, LSM from this CAFO could be applied to the field at the current rate for many centuries before soil copper concentrations would reach toxic levels.