Release And Migration Of Colloidal Phosphorus In Paddy Soil Under Different P Fertilization

Colloidal phosphorus (P) is an important form of P, widely existing in various environmental media. It constituted a part of P pool in soil, which was affected by soil physical and chemical properties, fertilizer application, rainfall, vegetation root system, etc. We collected literatures related to soil colloidal P, and summarized certain factors on occurrence and release of soil colloidal P. The field experiments on release and migration of soil colloidal P were carried out in paddy system. Size distribution of P, change of molybdate-reactive phosphorus (MRP) and molybdate-unreactive phosphorus (MUP) in paddy surface water under different fertilization were compared and analyzed. Contents and interrelation of elements on colloids and the active intensity of P in different sizes were explored. Effects of fertilization on total P, the mass of soil colloidal particles, colloidal P and dissolved P in soil profile were studied. The main results were shown as follow:1. Fertilization lead P concentrations of surface water arrived at peak. It reduced quickly in the first week, and maintained 0.12 mg P/L at late stage. Major component of P changed from particle P to dissolved P, and colloidal P occupied 7%～18% of total P, which could stably exist. Particle P and colloidal P were increased by manure application. Colloidal P content was small, and influenced by factors such as fertilization, adsorption, so the MRP and MUP in colloidal P constituted unsteadily. Fitting curve could be used for predicting the P loads in paddy suface water.2. P loads in surface runoff in paddy were impacted by both fertilization and rainfall. Particle P accounted for above 50% of total P, while colloidal P concentration was generally 0.01～0.02 mg/L. Manure increased export of particle and colloidal P by 6.0% and 29.4%, respectively. There were positive correlations among colloidal P, colloidal Fe, colloidal Al and colloidal TOC. The active coefficients of various P were: particle P>colloidal P>dissolved P.3. P fertilization mainly affected soil P distribution in top 30 cm soil layer. Long-term excessive fertilization eventually resulted in P accumulation in the topsoil.The mass of soil colloidal particles increased by soil depth, and manure played a positive role. It decreased remarkably in topsoil during the flooded period of rice production. Colloidal P occupied at least 85% of the P in a soil colloidal solution and 0.1%～2% of the total P in the soil. Compared with inorganic fertilizer, there was a remarkable effect in manure treatment. Changes of the mass of soil colloidal particles and colloidal P after rice harvest may be due to the vertical transport of colloidal P. MRP was the main part of colloidal P in soil profile after oilseed rape harvest. Colloidal P in topsoil under different treatment after rice harvest had no difference, including MRP and MUP, but dissolved P increaseed with the rate of fertilization.