A field plot experiment with 4 phosphorus application rates in 4 replications was conducted on the calcareous paddy soil in the Jianghan Plain under rice plant in the year 2005

in order to estimate the loss risk of phosphorus.Results show that: the P concentration in surface water has great relation with the P application rate

so considering of the environment impact

economic benefit and the need amount P of rice growth

we recommend the P application rate is 66 kgP2O5/hm2 by linear plateau model;during the days after P application

the concentration of P in surface water takes on a course that fall rapidly at first

then fall slowly and to be steady

and the P concentration of the surface water still keep high in 7 days after P application

so it is dangerous for P drainage;the logarithm model related to time can predict the concentration trend of the P(except SOP)

r is 0.715 1 ~0.963 9(P<0.05)

so we can utilize this model to predict the drainage safe time

and we find the safe time for water drainage is about 24 days after P application under the common P application rate;the soluble inorganic phosphorus(SIP) is main form of the total phosphorus(TP) in surface water

except the treatment P0

and the particulate phosphorus(PP) increases along with the increase of P rate

it indicates that the influence of PP can not be neglect when we estimate the P surface water contribute to the water eutrophication.