Macromolecule‐P associations and inositol phosphates in some chilean volcanic soils of temperate regions

Total organic P, humic and fulvic acid‐P associations and inositol phosphates in nine volcanic soils of southern Chile were determined. The concentration of organic P (Po) ranged from 654 to 1942 ppm accounting for 49% to 64% of total soil P. Phosphorus associated to humic (HA‐P) and fulvic acids (FA‐P) accounted for 51–68% and 32–49% of Po, respectively. Inositol penta‐ and hexaphosphates represented 42% to 67% of Po suggesting that significant amounts are associated with both humic and fulvic acids. Po content was significantly correlated to organic C, total soil P and HA‐P. HA‐P and FA‐P fractions obtained from the most representative soil were examined by dyalisis and gel filtration. While approximately 96% of HA‐P presented a molecular weight higher than 100,000 daltons, 53% of FA‐P had a molecular weight under 12,000 daltons. It is suggested that these more labile organic P forms would be more easily mineralized, thus increasing the available P pool.