Phosphorous fractionation of paddy fields and their relations with physical and chemical properties of soils (Case study: Some-e-Sara city, Guilan province)

Long-term effects of Rice (Oryza Sativa L.) cultivation with different management on soil P fraction are important to understanding from soil nutritional and environment point of view.Soil P fraction gives an idea about the soil supplying capacity to plants. This experiment was conducted to evaluate different soil P fractionation under paddy fileds condition and their relation with soil properties at rice root depth (0-30 cm).Soil samples were collected from 103 paddy fields at Some-e-sara city in Guilan provience with grids of 2x2 km.Soils were analyzed to determine of their characters (pH, CEC, T.N.V, Clay, O.C) and sequentialy extracted to determine organic and inorganic P fractions.The results showed total phosphorus concentration range between 218- 1677.5 (mean of 563), inorganic phosphorus 60-1427.5 (mean of 353 mg/kgsoil) and organic phosphorus with range of 25-525 (mean of 210). The persent of inorganic phosphorus were observed 62.6% of total phosphorus in comparison of organic phosphorus, 37.4%. Inorganic phosphorus fractionations in study area were Ca-p (mean=226), Al-p (mean=15.63), Fe-p (mean=220.4) and soluble and weak bounded phosphorus (Sol-p) (mean= 0.655 mg/kg soil), whereas the available phosphorus with mean of 29.02 mg/kg soil was more than Iranian paddy fields critical level.The Ca-p with pH,TNV, and OC%, Fe-p with pH, TNV, OC%, Clay content and CEC, Al-p with OC% and CEC, Sol-p with OC%, organic phosphorus with CEC, OC%, pH, TNV and Clay content available phosphorus with CEC, TNV and OC% showed significant correlation, respectively. The linear multiple regression equations the available phosphorus was affected from Al-p more than other fractions in rice fields.