Arsenate-induced Phosphate Release from Soils and its Effect on Plant Phosphorus

Adsorption of arsenic onto soil was investigated as a means of understanding arsenic-induced release of phosphate. In batch adsorption experiments As adsorption was accompanied by P desorption. At low As additions, the ratio As adsorbed: P desorbed remained constant. At higher As additions, P desorptionreached a maximum while As adsorption continued to increase. The P desorption maximum coincided with an increase in pH.Barley plants were grown on soils spiked with arsenate(0–360 mg As kg^-1) to investigate the effect on plant growth and P uptake. As arsenic concentration increased, above ground plant yield decreased and the plants showed symptoms typical of As toxicity and P deficiency. At low As additions to the soil, uptake of As and P by barley increased. At higher As additions P uptake decreased. It is argued that this was due to the change in As:P ratio in the soil solution. It is concluded that input of arsenic to thesoil could mobilise phosphate. Crop yield is likely to be affected, either due to reduced phosphate availability at low arsenic additions or arsenic toxicity at higher additions.