Copper Availability, Form, and Mobility in Soils from Three Annual Copper‐Enriched Hog Manure Applications

Abstract

AbstractRelatively high Cu concentrations occur in manure from hogs fed growth‐stimulating Cu levels. Concern exists that detrimental effects may occur in crop production from incorporation of the Cu‐enriched hog manure into agricultural soils. This research was conducted during three growth seasons to evaluate effects of Cu‐enriched hog manure applications on Cu availability, form, and mobility in one Alfisol and two Ultisols. Five field treatments applied to the three soils annually for 3 years were 33.6 and 67.2 metric tons/ha of wet manure from hogs on high‐Cu diets, Cu levels as CuSO4 equivalent to that in the manure, and a control. Copper concentrations in the hog feed ranged from 178 to 261 ppm during the 3 years. Amounts of Cu in manure used in the field experiments varied with Cu concentrations in the feed and ranged from 899 to 1,398 ppm. From 55.6 to 65.6 kg/ha Cu were incorporated into the soils over the 3‐years at the 67.2‐metric ton/ha manure rate. Application of these levels of Cu as either CuSO4 or Cu‐enriched hog manure did not decrease corn (Zea mays L.) grain yields on the three soils. In some cases, the Cu applications caused relatively small increases in Cu concentrations in corn ear leaves and grain. Diethylenetriaminepentaacetic acid (DTPA)‐extractable Cu data indicated that downward movement of Cu from Cu‐enriched hog manure application occurred in only one of the three soils. This soil contained relatively low amounts of clay and free Fe and Mn. Sequential Cu extraction data indicated that the applied Cu increased the potentially plant‐available soil Cu fractions and that a portion of the applied Cu reverted to relatively plant‐unavailable soil Cu forms.