Accumulations of copper in apple orchard soils: distribution and availability in soil aggregate fractions

The particle fractions of soil influence the retention and availability of heavy metal. However, the accumulations of Cu in aggregate size fractions of apple orchard soils due to the long-term application of Cu-based fungicides remain poorly understood. This study aimed to investigate the distribution and availability of Cu in various aggregate fractions of soils from different aged apple orchards. Soil samples were collected from orchards with 10, 20, 31, 45, and 50 years old. Soils were partitioned into four aggregate fractions (> 2000, 2000-1000, 1000-250, < 250 mu m) by dry sieving. Total soil Cu concentrations increased with increasing orchard ages, ranging from 29.1 to 147.9 mg kg(-1). The input Cu was mainly located in the < 250-mu m fraction for the 10-, 20-, 45-, and 50-year-old orchards, while it was mainly stored in the > 2000- and < 250-mu m fractions for the 31-year-old orchard soil. Generally, the Cu bioavailability and transferring capability have a tendency to increase with the increase of orchard age for both bulk soils and aggregate fractions. Additionally, among the four aggregate fractions, the < 250-mu m fraction had the greatest potential availability and mobility of Cu. The results of this study showed that sizes of soil aggregate fractions can significantly influence the retention characteristics of input Cu in orchard soils.