[Simulation of relationship between dissoluble phosphorus loss and runoff time]

The environmental sensitive phosphorus point of a cinnamon fluvo-aquic soil was 69.4 mg/kg (Olsen-P) evaluated by fitting soil Olsen-P and CaCl2-P content using Heckrath split-line model. The relationship between dissoluble phosphorus (DP) lost from runoff in soils applied different P rate and runoff time was studied using circular water method. The first-order kinetics model was used to simulate the dynamics of DP transported from soil to water with time. The results indicated that this model could simulate the transport suitably. When the applied P less than 400 kg/hm2, the velocity constant K which is average 1.095 h(-1) unchanged; while when the applied P rates were 800 and 1600 kg/hm2, K decreased by 17.2% and 38.9%, respectively. The exponent function was used to simulate the velocity of DP from soil to water with time and the results showed that it was a suitable model. When the applied P less than 400 kg/hm2, the velocity constant K' which is average 1.037 h(-1) unchanged; while when the applied P rate was higher than 800 kg/hm2, a declining tendency was found for K'. There was significant relationship between soil Olsen-P or CaCl2-P content and soil DPLP or VP0 when surface runoff occurred. This result showed that soil Olsen-P or CaCl2-P content could be used to direct the runoff risk as a gist of estimate soil environment.