Optimizing Extraction Process Organic Phosphorus Fractionation from Dark Brown Soil at Apple-pear Orchards

Dark brow soil at the apple-pear orchards at Yanji in the Korean Autonomous Prefecture of Yanbian in Jilin province was sampled for the experimentation on organic phosphorus fractionation. The process was optimized by using the Bowman-Cole method modified by Xiong Heng-duo and Fan Ye-kuan. The fractionation included the following major steps:(1) to the acidic soil pretreated with chloroform, 0.5 molL-1 of NaHCO3 were added with ultrasonic treatment for 10 minutes followed by oscillation for 30 minutes to extract the labile organic phosphorus into the supernatant; (2) to the soil left after the initial extraction, 0.1 molL-1 of NaOH was added with ultrasound for 10 minutes followed by oscillating for 4 hours to leach the stable and the moderately labile organic phosphorus fractions into the alkali solution; (3) to the above alkali supernatant, acid was added to adjust the pH to 3.00 to precipitate the highly stable organic phosphorus and allow the moderately stable fraction remain in the solution; and finally, (4) to the soil, 1 molL-1 of H2SO4 was added with a constant oscillation for 3 hours to extract the moderately labile organic phosphorus. In comparison to the existing methods, the current fractionation process on the acidic orchard soil in north China appeared to have optimized the conditions with improved efficiency.