Distribution of Forms of Copper and their Association with Soil Properties and Uptake in Major Soil Orders in Semi-arid Soils of Punjab, India

Profiles of semi-arid-zone soils in Punjab, northwestern India, were investigated for different forms of copper (Cu), including total Cu, diethylenetriaminepentaacetic acid (DTPA)–extractable Cu, soil solution plus exchangeable Cu, Cu adsorbed onto inorganic sites, Cu bound by organic sites, and Cu adsorbed onto oxide surfaces. When all soils were considered, total Cu content ranged from 7 to 37 mg kg ⁻¹, while DTPA-extractable and soil solution plus exchangeable Cu contents ranged from 0.30 to 3.26 mg kg ⁻¹ and from 0.02 to 0.43 mg kg ⁻¹, respectively. Copper adsorbed onto inorganic sites ranged from 0.62 to 2.6 mg kg ⁻¹ and that onto oxide surfaces ranged from 2.0 to 13.2 mg kg ⁻¹. The Cu bound by organic sites ranged from 1.2 to 12.2 mg kg ⁻¹. The magnitudes of different forms of Cu in soils did not exhibit any consistent pattern of distribution. Organic matter and size fractions (clay and silt) had a strong influence on the distribution of different forms of Cu. The content of all forms of Cu was generally greater in the fine-textured Alfisols and Inceptisols than coarse-textured Entisols. Soil solution plus exchangeable Cu, Cu held onto organic sites, and and Cu adsorbed onto inorganic sites (crystalline) had significant positive correlations with organic carbon and silt contents.The DTPA Cu was positively correlated with organic carbon, silt, and clay contents. Total Cu content strongly correlated with silt and clay contents of soils. Among the forms, Cu held on the organic site, water soluble + exchangeable Cu, and Cu adsorbed onto oxide surface were positively correlated with DTPA-extractable Cu. The DTPA-extractable Cu and soil solution plus exchangeable Cu seems to be good indices of Cu availability in soils and can be used for correction of Cu deficiency in the soils of the region. The uptake of Cu was greater in fine-textured Inceptisols and Alfisols than coarse-textured Entisols. Among the different forms only DTPA-extractable Cu was positively correlated with total uptake of Cu.