Field surveys on the outflow characteristics of nitrogen and phosphorus from farmland soil were conducted. The concentration of NH4-N in the pore water in the paddy fields in pooling period was found to be the highest in soil layers at the depth 10cm below the surface. The concentration of nitrate nitrogen (NO
2, 3-N) was lower than 1.0mg /l in soil layers 90cm below the surface, although the concentration increased in each layer after harvesting rice. A higher concentration of NO
2, 3-N was detected in the paddy field where a secondary crop of barley is cultivated, but the paddy fields generally did not contribute to nitrate contamination of the groundwater. The median diameter of the soil particles in the run-off from farmland during rainy weather was below 10μm. Run-off phosphorus was mainly contained in a fine particle fraction over 0.22μm. The concentrations of P in the soil particles over 1μm were as large as 5.5mg/g and 3.9mg/g for paddy fields and farmlands respectively. Run-off of phosphorus-accumulated farmland soil particles should be carefully attended as the eutrophication factor.
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