Abstract: This paper studied the time series variations of agricultural non-point source nitrogen and phosphorous losses and their relationships with rainfall-runoff in the Daijiagou small watershed (0.67 km²) in Three Georges Reservoir area, based on the 2007-2009 field observation data. In 2007-2009, the peak values of the rainfall and runoff in the watershed had the same variation trend, with the correlation coefficient as high as 0.904. The total nitrogen (TN) and total phosphorus (TP) losses also showed a same variation trend, but the TN loss was more sensitive to the variation of rainfall-runoff, as compared to TP loss. The TN loss fluctuated with rainfall-runoff, but the TP loss showed an increasing trend year by year. The variation pattern of N/P ratio accorded with that of TN concentration, and showed a good coupling relationship with the runoff fluctuation. The peak time of the cumulative percentage of rainfall-runoff was not consistent with that of TN and TP losses, suggesting that the agricultural non-point source nitrogen and phosphorous pollution in the watershed was of random and dispersive, and there was no strict parallelism relationship between the nitrogen and phosphorous pollution.

Key words: Predacious ladybird, Biological control efficiency, Function assessment