The status and dynamics of cadmium in a savanna soil with long history of phosphate and farmyard manure fertilization

Abstract

Long-term applications of phosphatic fertilizers can lead to cadmium (Cd) accumulation in soils. This study was conducted to investigate the effect of phosphatic fertilizers with or without farmyard manure (FYM) on the Cd dynamics of a savanna Alfisol after 50 years of continuous cultivation. Total Cd (Cd_T) was very low (13 – 54 µg kg⁻¹) in the surface layer, and decreased sharply below the surface layer. The DTPA extractable Cd accounted for between 16 and 77% of Cd_T in the surface layer of the soil and between 3 and 5% in the subsurface layer. Mass balance calculations to assess the levels of anthropogenic Cd input indicated a net positive mass balance of 2.3 g ha⁻¹ in NPK fertilized field, whereas the FYM and FYM + NPK fertilized fields lost 113 and 187 g ha⁻¹ respectively after 50 years of cultivation as compared to a natural or an uncultivated site. Although net positive balances of Cd occurred in the NPK-fertilized plots, the increases were not significant to curtail or regulate current levels of phosphate fertilization in this savanna soil.

Keywords:

• Cadmium
• phosphate fertilizer
• soil management
• savanna

Acknowledgements

I thank the Alexander von Humboldt Foundation for the fellowship that enabled this work to be done. The facilities provided by the Institute of Soil Science, University of Giessen, and Prof. Dr Peter Felix-Henningsen, Director of the Institute, are duly acknowledged.