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| Titel |
Temporal dynamics of available and microbial phosphorus and organic phosphorus mineralization in a grassland soil |
| VerfasserIn |
Frank Liebisch, Fabrizio Keller, Emmanuel Frossard, Olivier Huguenin-Elie, Astrid Oberson, Else Bünemann |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036259
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| Zusammenfassung |
| Turnover of phosphorus (P) through the microbial biomass and P mineralization have been
reported as two main biological factors controlling P availability in soils. This is
particularly true for grassland soils where organic matter is accumulated in the
topsoil and microbial activity is high. The amounts of plant available inorganic P
and microbial P can fluctuate over the season, but their interaction and responses
to changes in environmental conditions, fertilization and cutting are not yet well
understood. Also, gross P mineralization has not yet been measured in grassland
soils.
We studied P mineralization and immobilization in a species rich grassland managed at
low intensity (with three harvests per season) under different P inputs. The trial was
established in 1992 in Watt (Switzerland). Three different P input treatments were selected:
no P (NK), mineral P (NPK) and organic P (NPKorg) fertilization, with 17 kg P ha-1yr-1
applied as superphosphate and slurry, respectively (rates according to Swiss fertilizer
recommendations).
We used two different approaches. Firstly, available (anion exchange resin extractable)
and microbial P (hexanol labile P) were measured in fresh samples periodically taken
throughout the vegetation period. Secondly, an isotopic dilution technique was applied on
composite topsoil samples (0-5 cm) to determine rates of basal P mineralization and
microbial immobilization of P in an incubation experiment.
During the season available P ranged from 0.9-3.5, 5.3-11.2 and 1.9-6.7 mg kg-1 soil-1
and microbial P from 20-44, 43-59 and 61-93 mg kg-1 soil-1 in NK, NPK and NPKorg,
respectively. Thus, microbial P was highest in NPKorg whereas available P was highest in
NPK. Both P pools were lowest in NK. Average annual yield was lowest in NK (4.5 t ha-1),
NPKorg (6.5 kg ha-1) and highest in NPK (7.5 t ha-1). However, no consistent
relationship between changes in microbial and available P and plant productivity
was found. Changes in weather conditions were reflected by changes in available
and microbial P measured in the field. Phosphorus flushes were observed after dry
periods (microbial P reduced and available P increased). Whereas fluctuations show
microbial P release and P immobilization, an expected counteraction of microbial and
available P could not be fully confirmed. In the incubation experiment microbial and
available P were similar to average values in the field. A higher respiration rate
measured in NPKorg indicated a higher microbial activity than in the other two
treatments. Despite the differences in microbial P and respiration, the 33P recovery in
the microbial biomass between 3 and 30 days of incubation was about 30% in all
treatments.
In conclusion we found complex interactions of available and microbial P with climate,
fertilization, sward cutting and plant growth. An increased immobilization of P indicated by
higher microbial P in the organic fertilized treatment was not confirmed in the isotope study.
Gross and net mineralization data are still under analysis and will be presented at the
conference. |
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