Effect of Long-Term Fertilization on Cd, Zn, Se and As in the Field Soils of Northern Japan, Hokkaido.

The Abashiri area in Hokkaido Prefecture is one of the most important agricultural areas in northern Japan. As a result of long-term, excessive Phosphorus (P) fertilization, in this area, most of the agricultural soil has highly accumulated available P. P fertilizer can potentially serve as a source for cadmium (Cd), Arsenic (As), and Selenium (Se) accumulation in croplands. In addition to this, typically about 40 Mg ha^-1 of animal manure have been applied every three years. The manure in this area contains 120-650 mg kg^-1 of Zinc and regarded as remarkable zinc source. In order to assess the increase of Zn, Cd, As, and Se with long-term fertilization, we evaluated the amounts of these metals in soil before and after agricultural use. We sampled the soils at a depth of 0 to 80 cm from five field cites and adjacent forest of each field for comparison in July 2013. Soil Zn, Cd, As, and Se was measured by Atomic Absorption Spectrometry and a hydride generation system following digestion of the sample with HClO₄-HNO₃-HF. As a result, the amounts of Zn, As, and Se observed for surface soils (0-20 cm) in the fields tended to be higher (84-112 mg Zn kg^-1; 0.9-3.1 mg As kg^-1; 0.16-0.58 mg Se kg^-1) than those for forest soils (73-96 mg Zn kg^-1; 0.7-2.7 mg As kg^-1; 0.03-0.43 mg Se kg^-1). It was considered that the long-term use of organic or inorganic fertilizers increased these metals. For Cd, however, except of one area, the Cd content of surface soils was higher for forest soils (0.35-2.43 mg Cd kg^-1) than field soils (0.05-6.65 mg Cd kg^-1), Cd increase due to agriculture was not clearly observed.