Abstract: Aiming at the characteristics of water and nutrient management of rice cultivation,a model (precipitation-runoff-N loss simulation model,PRNSM) simulating rainfall-runoff-N-loss from paddy field was established with major parameters specified based on the data of field measurements and from the literature. Simulated calculation was carrid out on the basis of the daily precipitation data in the 56 years from 1951 to 2006,using a self-written computer program to study relationship of runoff and N loss therewith with rainfall in Nanjing. Results show that besides amount of rainfall and flux of runoff,interval between the date fertilizer was applied and the date relatively strong runoff took place was also a major factor affecting amount of N loss with runoff. Further analysis revealed that the first 7 days after fertilization is the key period to reducing N loss with runoff during the rice growth period,and transplanting rice in mid-June contributes to the reduction of N loss with runoff.

Key words: runoff in paddy field, N loss, system simulation