Study On Impact Factors And Potential Evaluation Index Of Soil P Loss In Runoff

118 Soil samples were collected from the middle reaches of The Yangtze River in Hubei province to research the impact factors of soil P runoff, and lab experiments were done to study the sorption-desorption character, the threshold DPS(Degree of Phosphorus Sorption) of the main soil styles in Hubei, and the potential of different land utilization styles on red soil. The results obtained were as follows:1. 118 soil samples were classfied into paddy field soil, red soil and fluvo-aquic soil styles, analyze the relationship between the pH, OM, Olsen-P (Mehlich-3P), active Fe, active Al, exchangeable Ca, exchangeable Mg, available K, <0.001, <0.005, <0.01, <0.05mm soil particles and the CaCl₂-P through the Stepwise method in SPSS, the impact factors of soil P loss are different, the active Fe(X₂) and Olsen-P(X₁) are the factors to impact the P loss in paddy soil, and the correlation equation is Y=0.027X₁- 1.088X₂+8.669; the factors to impact the P loss in red soil are active Fe(X₂), then the Olsen-P (X₁)and active Al (X₃)next, and the correlation equation is Y= 0.052X₁ - 1.241 X₂ -0.03X₃+10.305, in the fluvo-aquic soil, the main factors are exchangeable Ca(X₂), Olsen-P(X₁) and OM(X₃), the correlation equation is Y= 0.037X₁-1.001X₂- 0.012X₃ +12.011. The concentration of CaCl₂-P(Y) can be predicted through these 3 models.2. The Olsen-P, Mehlich-3P, deionized water-P and CaCl₂-P were linearly related to TP (total phosphorus), and the 4 methods were linearly related to each other (R²=0.6291⁰.8010), it shows that the method used in environment and agriculture has something in common, and the concentrations for a given soil vary as M-3P>Olsen-P> deionized water-P> CaCl₂-P.3. Lab experiment were done to study the sorption-desorption character on the 8 agrotype in Hubei province. The Langmuir equation can describe the sorption-desorption character of soil P, and the Q_m, desorption ratio, PSI, desorption ratio per sorption a can reflect the soil P loss potential through Principal Component Analysis in SPSS. The Q_m is related to PSI, and PSI is easy to get, desorption ratio contributes great to the Principal Component, so PSI and desorption ratio can be used together to forecast the potentiality of soil P loss.4. The threshold DPS of 8 styles soil is 19%, higher than classifying 8 styles into 3 styles (12.8%～19%), so the scale should be considered when using DPS to evaluate the potential of the soil P loss. In this research, the threshold DPS for fluvo-aquic soil, red soil and paddy soil are: 19.0%, 13.2%,12.8%, and the corresponding CaCl₂-P concentration are 2.21,0.92,0.57 mg.L^-1 for each style soil. The four ranges None, Low, High and Very High are assigned different P loss ratings, for fluvo-aquic soil: <5%, 5～10%, 10～19%, >19%, red soil <7%, 7～13%, 13～20% and paddy soil:<6%,6～13%, 13～17%, >17%.5. Use the impact factors of soil loss to evaluate the potential of P loss risk in the dry farmland and paddy soil, namely the P loss risk present the opposite of the active Fe concentration, the potential of P loss in different land utilization type is dry farmland>tea garden>paddy soil>wasteland, the order is the same compare with the risk forecast made by the DPS, but, it still has something different compare with the sorption-desorption character, such as to the paddy soil. In conclusion, it is stable to use the impact factors to evaluate the potentiality of P loss risk, so it should be taken in consideration during the coming research on P loss risk.