Plant and Soil

, Volume 147, Issue 2, pp 243–250 | Cite as

A new method for estimating gross phosphorus mineralization and immobilization rates in soils

  • Xiaoming Zou
  • Dan Binkley
  • Kenneth G. Doxtader


Phosphorus availability in soils is controlled by both the sizes of P pools and the transformation rates among these pools. Rates of gross P mineralization and immobilization are poorly known due to the limitations of available analytical techniques. We developed a new method to estimate P transformation rates in three forest soils and one grassland soil representing an Alfisol, an Ultisol, and Andisol, and a Mollisol. Three treatments were applied to each soil in order to separate the processes of mineral P solubilization, organic P mineralization, and solution P immobilization. One set of soils was retained as control, a second set was irradiated with Γ-rays to stop microbial immobilization, and a third was irradiated and then autoclaved, also stop phosphatase activity. All three sets of samples were then incubated with anion exchange resin bags under aerobic conditions. Differences in resin P among the three treatments were used to estimate gross P mineralization and immobilization rates. Autoclaving did not affect resin-extractable P in any of the soils. Radiation did not alter resin-extractable P in the forest soils but increased resin-extractable P in the grassland soil. This increase was corrected in the calculation of potential P transformation rates. Effects of radiation on phosphatase activity varied with soils but was within 30% of the original values. Rates of P gross mineralization and immobilization ranged from 0.6–3.8 and 0–4.3 mg kg-soil-1 d-1, respectively, for the four soils. The net rates of solubilization of mineral P in the grassland soil were 7–10 times higher than the rates in forest soils. Mineralization of organic P contributed from 20–60% of total available P in the acid forest soils compared with 6% in the grassland soil, suggesting that the P mineralization processes are more important in controlling P availability in these forest ecosystems. This new method does not require an assumption of equilibrium among P pools, and is safer and simpler in operation than isotopic techniques.

Key words

forest grassland nutrient cycling organic P P transformations 


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Copyright information

© Kluwer Academic Publishers 1992

Authors and Affiliations

  • Xiaoming Zou
    • 1
  • Dan Binkley
    • 2
  • Kenneth G. Doxtader
    • 3
  1. 1.Terrestrial Ecology DivisionUniversity of Puerto RicoSan JuanUSA
  2. 2.Department of Forest SciencesColorado State UniversityFt. CollinsUSA
  3. 3.Department of AgronomyColorado State UniversityFt. CollinsUSA

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