Abstract: It was significant to study the nitrogen and phosphorus losses from surface runoff in double cropping rice filed for guiding the rational fertilizer and protecting water environment.The surface runoff losses under different nitrogen and phosphorus application in double cropping rice field in Hunan was studied based on field experiment data combining with runoff plot.The results showed that both nitrogen and phosphorus concentrations increased with application increasing in single runoff.Ammonium nitrogen and saltpetre nitrogen were the predominant forms of nitrogen surface runoff.Ammonium nitrogen was dominant in prophase of double rice growth season and saltpetre nitrogen in anaphase.The ratios of dissoluble phosphorus to total phosphorus of runoff water were 11.0%～94.0%.Nitrogen and phosphorus losses from surface runoff under their different application were 3.710～7.290kg·ha-1 and 0.200～0.320kg·ha-1,and erosion coefficients were 1.870%～3.771% and 0.327%～0.966%.There was good linear correlation between nitrogen and phosphorus losses from surface runoff and their application.Their coefficients were 0.978 and 0.997.Reducing nitrogen and phosphorus application in double cropping rice filed appropriately could decrease the losses from surface runoff and mitigate damage to surface water quality.

Key words: Hunan, Hunan, Nitrogen and phosphorus, Double cropping rice field, Loss from surface runoff