Submitted to: World Journal of Agricultural Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 14, 2010
Publication Date: June 14, 2011
Citation: Ippolito, J.A., Ducey, T.F., Tarkalson, D.D. 2011. Interactive Effects of Copper on Alfalfa Growth, Soil Copper, and Soil Bacteria. World Journal of Agricultural Sciences. 3(2):138-148. Interpretive Summary: Copper sulfate foot baths are disposed of in wastewater lagoons that are utilized for irrigation purposes. We investigated the effect of copper applications to two soils typically found in south central Idaho in terms of alfalfa growth, soil extractable copper content, and soil microbial community diversity. Copper applications up to 250 mg/kg did not affect alfalfa growth, but above 100 mg/kg increased alfalfa Cu content. Forty-eight to 80% of the added Cu was still available for plants at the end of the study. To prevent excessive alfalfa Cu accumulation and negative impacts on the soil microbial community, it is recommended that available soil Cu not exceed 63 mg/kg in these agroecosystems.
Technical Abstract: Copper sulfate foot baths are a management practice used by dairy farms in an effort to control hoof infections. As an unintended consequence, agricultural soils experience Cu accumulation when spent foot baths are disposed of in wastewater lagoons that are utilized for irrigation purposes. We investigated the effect of Cu applications (up to 1000 mg/kg) to a Xeric Haplocalcid (Declo series) and a Typic Calciaquoll (Logan series) on alfalfa (Medicago sativa) growth and Cu concentration, soil total and diethylenetriaminepentaacetic acid (DTPA)-extractable Cu, and the soil microbial community diversity using ribosomal intergenic spacer analysis (RISA). Copper application up to 250 mg/kg did not affect alfalfa growth; above 500 mg/kg alfalfa did not grow. The 100 and 250 mg/kg Cu application rates increased alfalfa Cu content grown in Declo soil, while the 250 mg/kg Cu application rate increased alfalfa Cu content when grown in the Logan soil. Regardless of initial application rate, 48 to 80% of the added Cu was still plant-available at the end of the study. Comparing DTPA-extractable Cu to alfalfa Cu concentrations, 63 or 95 mg/kg of DTPA-extractable soil Cu for the Declo and Logan soils, respectively, would be detrimental in terms of cattle dietary Cu intake. For Declo soils, microbial diversity remained relatively stable across all Cu application rates; Logan soils saw a peak in microbial diversity at the 50 mg/kg Cu application rate. Cluster analysis revealed differences in the microbial RISA profiles between the lower and higher Cu application rates. To prevent excessive alfalfa Cu accumulation and negative impacts on the soil microbial community, it is recommended available soil Cu not exceed 63 mg/kg in agroecosystems associated with these soil series.