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This paper reviews current information about potassium (K) in the soils of New Zealand, based on work conducted since the 1920s. The forms of K existing in soils are discussed and related to the K status of the genetic soil groups. The methods used in New Zealand to assess Ksupplying power, K-releasing power, and plantavailable K are discussed. The historical development of the methods for computing the K fertiliser requirements of pastures and crops in New Zealand is reviewed with emphasis on the Computerised Fertiliser Advisory Service (CFAS) established in 1984. The CFAS model is discussed and amendments are suggested.

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