Corn response to six annual Cu-enriched pig manure applications to three soils

The increasing use of land application of organic wastes presents a potential pathway for metals to enter the environment and cause phytotoxicity. Studies to evaluate the response of corn (Zea mays L.) to annual applications of Cu-enriched pig manure or CUSO₄ were established as ongoing field experiments in 1978 on three soils. The soils varied in texture from fine sandy loam to clay loam and ranged in CEC from 5.0 to 12.3 cmol(+) kg^?1. Five treatments in each field experiment consisted of a control, low and high Cu-enriched pig manure levels, and low and high CuSO₄ levels. After 6 yr 638 Mg ha^?1 of wet Cu-enriched pig manure containing from 185 to 198 mg Cu kg^?1 had been applied for the high treatments on the three soils. The Cu-enriched pig manure, which contained 1290 mg Cu dry kg^?1, was produced by pigs fed diets with 242 mg Cu kg^?1. In the sixth year, leaf blade Cu concentrations were increased by ≤ 3.3 mg kg^?1 due to the high Cu treatments but remained in the middle of the Cu sufficiency range. Grain Cu was 73 to 84% lower than blade Cu and was unaffected by the treatments. The DTPA (diethylenetriaminepentaacetic acid) extractable Cu was not related to either leaf or grain Cu levels. However, the DTPA extractable Cu was linearly related, r = 0.92, to applied amounts of Cu in the three soils. Overall, this research indicated that application of up to 638 Mg kg^?1 of wet Cu-enriched pig manure did not cause an environmental hazard.