Phosphate Rich Soil Additive Baked Pig Manure Effectively Reduces Arsenic Concentration in Japanese Mustard Spinach (Brassica rapa var. perviridis) Grown with Arsenic Contaminated Irrigation Water

A pot experiment was conducted to assess the efficiency of baked pig manure (BPM) application in Japanese andosol to reduce the arsenic (As) concentration in Japanese mustard spinach (JMS) (Brassica rapa var. perviridis) grown with As-contaminated irrigation water. Irrigation water was artificially spiked with As to 0.5 mg L-1 dissolving di-sodium hydrogen arsenate heptahydrate (Na2HAsO4.7H2O). BPM was applied to soil at the rate of 1, 2, and 3%; each treatment had four replications. The plant was grown for 30 days. Plant samples were analyzed for As and other elements. Plant As concentration decreased significantly with BPM application and based on the plant dry weight (DW) the As concentration reduced by 39, 52 and 66%, with the application of 1, 2 and 3% BPM, respectively, compared with those of control plant. There was no significant change in the As uptake (µg plant-1) after the application of BPM. Plant FW and DW increased significantly with increasing amounts of BPM, which might function to decrease the As concentration in plants as ‘dilution effect’. The phosphorus (P) contents of JMS increased significantly with BPM application, whereas the Fe, K and Mg contents decreased. The decreased As concentration and increased P concentration in plant indicated the competitive absorption of As and P in plant but this effect was not so strong because the As uptake (µg plant-1) was not significantly reduced. Moreover, BPM might have properties that enable the adsorption of As because BPM contained charcoal due to the baking treatment. It is possible that the surface of BPM might adsorb As and thereby hindered the As absorption by the plant root. It is suggested that the phosphate rich BPM could be an environment friendly, cost effective and non-toxic soil additive for reducing As concentration in vegetable plant grown with As-contaminated irrigation water