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Phosphorus Buffering Index (PBI) is used in conjunction with the Colwell Phosphorus measurement and gives an interpretation of a soils ability to “lock-up” P. Soils with a high PBI will quickly bind P to “exchange sites” and make it unavailable for plant uptake. Conversely, soils with a low PBI will lock up only small amounts of P, leaving the majority of fertiliser applied P available for plant uptake.
Managing high PBI soils generally involves applying higher rates of P fertiliser. Doing this over many years will gradually fill more and more exchange sites, therefore leaving more fertiliser P available for the growing crop.
In some Australian soils, where PBI is particularly low, phosphorus leaching can occur.