Chemical soil test prediction of pasture responses to potassium on recent soils of the South Island west coast

Abstract

Pasture yield responses to potassium (K) fertiliser were measured at 13 sites which had low levels of exchangeable K but varying amounts of non-exchangeable K. Of soil tests which measured available K (STK), exchangeable K (K_ex), and non-exchangeable but plant-available K (TPBK) in the top 7.5 cm of soil, K_ex gave the best correlation with relative yield. Further down the profile where exchangeable levels were low but non-exchangeable K levels were very high, only the TPBK test indicated the size of this potential source of K. Information from these soil tests can be used in mathematical models to predict fertiliser requirements for pasture.

Keywords:

• potassium
• soils
• soil test
• analytical methods
• reserve K
• exchangeable K
• plant-available K
• plant response