TRANSFORMATIONS OF ORGANIC PHOSPHORUS SUBSTRATES IN SOILS AS EVALUATED BY NaHCO3 EXTRACTION

The sodium-bicarbonate (NaHCO3) method of Olsen et al. was primarily designed to extract inorganic P (P1) and to correlate this P-pool with plant response. This procedure was used to follow the transformations of organic P (P0) substrates in soil. Various commercial P0 substrates were added to a sandy loam soil, and were extracted immediately and after 1 to 18 days of incubation at field capacity. Glycerophosphate and all 3‘ nucleotide components of RNA were completely mineralized and accounted for in the NaHCO3 solution after 3 days. While RNA degraded in 18 days, sodium inositol hexaphosphate (Na-phytate) was relatively unaffected during this time and unrecoverable in the NaHCO3 solution upon immediate extraction. Thus, the labile compounds, like RNA, its four 3’ nucleotides, and glycerophosphates were recoverable in the 0.5-M NaHCO3-extracting solution (pH 8.5) of Olsen et al., while the Na-phytate, a relatively resistant compound, was not. Native P0 was only slightly affected, however. A relatively constant amount of native P0 was extracted, irrespective of extraction periods lasting 0.5 to 6 h.