Influence of soil characteristics and leaching rate on copper migration: column test

Soil copper (Cu) supply is used to correct Cu deficiency in many crops grown in southern Mediterranean areas. Oversupply of this fertilizer may contaminate soil and groundwater. This study aims to assess Cu migration in different soils of Moroccan agricultural areas. Three soil samples were collected from different areas. For each soil, three annual leaching rates were tested: 35 mm, 237 mm, and 565 mm for a sandy soil; 35 mm, 70 mm, and 140 mm for a clay calcareous soil; and 35 mm, 103 mm, and 247 mm for silty clay soil. The leaching experiments were conducted in columns filled identically up to 30 cm with each soil sample. Then, 0.6 mg of Cu kg^-1 was added to the soil surface in the sulfate form (CuSO₄.5H₂O). The results showed that soil Cu loss increased mainly with leaching rate: y = 0.004 x - 0.10 (R² = 0.97) where y: soil Cu loss (10^-4 meq 100 g^-1) and x: leaching rate (mm). The regression analysis did not reveal a significant influence of the soil properties on Cu leaching. However, the Cu loss seems insignificant regarding the no recurrence of high annual leaching rate (over 500 mm), in south Mediterranean areas. Also, soil Cu accumulation risk occurred in all studied soils. For sandy soil, available Cu content was 78% higher in the top layer (0-10 cm) than its content in the middle (10-20 cm) and lower (20-30 cm) layers. Furthermore, a release of bioavailable Cu was recorded in silty clay and clay calcareous soils at a leaching rate of over 70 mm.