The amounts of N and P accumulated in farmland soils of 50 cm depth were equivalent to the amount of chemical fertilizer supplied for 50–70 years. The values of N/P of surface soils in farmlands were 1.0–4.3, lower than expected. The median diameter of soil particles in run-off waters was generally less than 10 μm. The mean values of particulate fractions over 1 μm and over 0.22 μm were 19% for N, 27% for P, and 39% for N, 64% for P respectively. Fine particles of soil containing concentrated phosphorus should be carefully monitored as potential sources related to eutrophication.
Study on the potential of farmland soils as non-point sources of nitrogen and phosphorus in Japan
M. Ukita, X. Shi, T. Higuchi, Y. Arkin, M. Fukada; Study on the potential of farmland soils as non-point sources of nitrogen and phosphorus in Japan. Water Sci Technol 1 January 2006; 53 (2): 119–130. doi: https://doi.org/10.2166/wst.2006.045
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