Accumulation and availability of copper in citrus grove soils as affected by fungicide application

Purpose Copper is a trace element of environmental concern. Repeated applications of Cu-containing fungicides have resulted in a large scale of Cu contamination in agricultural soils. However, limited information is available regarding Cu accumulation and availability in soils under citrus production in the Indian River Area, South Florida, which has received increasing amounts of Cu fungicides to control canker and other diseases. The purpose of this study was to investigate Cu transformation, availability, and mobility in soils as affected by external Cu loading and soil properties. Materials and methods Soil samples (n= 18) were collected from representative commercial citrus groves in the Indian River area. These samples were characterized to understand the accumulation, availability to plant, and leaching loss, as influenced by soil properties, agricultural practices, and Cu fungicide inputs. Results and discussion Significant accumulation and increased availability and mobility of Cu occurred in the soils with increasing citrus production period. Soil acidification enhanced Cu leaching in soil profiles. Available Cu estimated by Mehlich-3 or NH4OAc extraction was highly correlated with total recoverable Cu, whereas the relationship between CaCl2-extractable Cu and total recoverable Cu was affected by soil pH, with a greater slope of the relationship curve at soil pH <6.5. Vertical movement of Cu in a soil profile was more pronounced at pH <6.5. A large portion of soil Cu was present as organically bound, ranging from 43% to 62%, which was significantly correlated with both recoverable Cu and Mehlich-3-extractable Cu (P <0.001). Conclusions Significant accumulation of Cu occurred in citrus grove soils due to anthropogenic inputs, and the availability and mobility of Cu in the soils were related to Cu accumulation and soil pH. Copper migration from Cu-contaminated soils to the environment was reduced when soil pH was 6.5 or higher.