| A field experiment was conducted to study dynamic changes in ammonium（NH+4-N）, nitrate（NO-3-N） concentrations, dissolved total N（DTN）, total N（TN）, total P（TP） and dissolved total P（DTP） concentrations in the surface waters of paddy fields applied with different treatments of N and P fertilizers in the northern region of Erhai Lake. Results showed that TN and DTN peaked after 1~3 days, and decreased rapidly and then leveled off after 9 days of the basal fertilizer applied, while TN and DTN reached their respective peak values in concentrations quickly during milk stage. Dynamic changes of DTN fitted a quadratic equation（Y=AX2+BX+C）. NH+4-N peaked 3~5 days after the basal fertilizer applied, but NH+4-N peaked 1~2 days after the milk fertilizer applied. TP and DTP concentrations were exponentially declined after basal fertilizer application. However, there were no differences in these indexes 12 days later, this change could be described with an exponential equation（Y=C0×ekt, k<0）. Therefore, 9 days after fertilizing were the key period for controlling the N loss from the paddy fields, but two weeks for controlling the P loss. Fertilizing season should avoid rainfall period to reduce nutrient losses through runoff. |
