Abstract
Two Andosol field plots had been spread with two kinds of sewage sludge compost twice a year for twenty-odd years. since 1978, and corn (Zea mays L.) and barley (Hordeum vulgare L.) were grown in summer and in winter every year, respectively. 1) The contents of zinc and cadmium in the upper soil horizon (0 to 10 cm depth) were increased during the first ten years by the application of H compost (sewage sludge compost mixed with rice husks) and S compost (sewage sludge compost mixed with sawdust) and thereafter, the rates of increase became small or non-existent during the next ten years. A similar pattern was found for lead in the plot amended with H compost. The contents of copper in the plots amended with H and S composts and lead in the plot with S compost were similar to the values in the original soil. 2) Lateral movements of zinc and cadmium in the soil were clearly observed at the borders of plots in the examination of the cross direction sampling over the borders, and movements were probably caused by a mechanical transfer of the soil during cultivation. 3) The total amounts of zinc found in the upper soil horizon in the H compost and neighboring chemical fertilizer plots were 53.4% and 6.5%, respectively, the zinc added by the H compost. The zinc in the chemical fertilizer plot was transferred by lateral movement from the H compost plot. About 43% of zinc added by the H compost was found in the middle soil horizon (10 to 20 cm depth) in our previous report. Thus, almost all zinc added by composts was retained in the agricultural land.
