Comparison of soil analytical methods for estimating plant-available potassium in highly weathered soils

Context The NaHCO3-extractable soil K test (Colwell K) is the most frequently used method for across Australia, but there still uncertainty about suitability of testing guidelines heavy-textured soils.Aims To determine whether Colwell suitable predicting plant-available on loam- and clay-textured types developed from highly weathered parent materials in Western Australia (WA).Methods Nine methods were to 21 with a wide range properties collected three depths northern, central southern farmlands WA.Key results Quartz K-feldspars dominant minerals all soils, while limited white mica (1–2%) was identified less than 10% samples. amount extracted by silver thiourea only 70% amounts NaHCO3 NH4OAc. Soil non-exchangeable nitric acid sodium tetraphenyl borate similar pools, aqua regia 1–6times higher these values.Conclusion There no systemic difference or proportional bias between NH4OAc K, both had good model performance (R2>0.86) total uptake wheat single growing season soils.Implication In this diverse soils formed materials, reliance exchangeable plant suggests that will be vulnerable rundown due negative balances.