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