Abstract
A case study was conducted with a paddy field in Aomori Prefecture to examine the contribution of lateral percolation to the amount of outflowing water and the quality of water outflowing from a paddy field. The result showed that about a half of the water outflowing from a paddy field was due to vertical percolation and the contribution of lateral percolation was little. Surface runoff of nitrogen and phosphorus during a plowing and irriganting period accounted for about 70% and 60%, respectively, of their total export from a paddy field during a cropping period. Mass balance of nitrogen suggested that the paddy field examined was a week exhaust type.
