The significance of stable P forms in soilSabina BraunSLU
Photo: Jenny Svennås-Gillner, SLU
Soil P test(P-AL)
Which crop?
Expected yield?
Fertilizer recommendation
ßIs this the best test?
What about P availability?
For all soils?
Solution P Labile P Stable P
SOIL P TEST TARGET TODAY
So what are we doing?
Long-term fertility experiments
Photo: Magnus Simonsson och Gunnar Börjesson.
P-balancesChanges in P pools
Sink methods
Iron oxide coated filter papersPhoto: Sabina Braun
Dialysis membrane tube filled with ferrihydratePhoto: Sabina Braun
P desorption rates
Isotopic exchange kinetics31P
31P
31P31P
31P
31P 31P
31P
31P
33P
31P
31P
31P
31P
33P33P
33P
31P
33P31P
31P
31P
31P
31P
31P
P exchange ratesAmount of exchangeable P
Sorbed soil P
Summary• P balances over 50 yrs
• Changes in P pools
• Desorbable P
• Exchangable P
• Soil properties
In the end: A model to more accurately predict the plant-available P pool, considering both:
– The size of the labile and stable P pool
How should it be measured?
and
– The transfer of P between labile and stable pools
What soil properties control this transfer?
Transfer between
pools
Size oflabile pool
Which crop?
Expected yield?
Fertilizerrecommendation
ß Estimated by relevant soil properties