Context: The NaHCO₃-extractable soil K test (Colwell K) is the most frequently used method for soil K across Australia, but there is still uncertainty about the suitability of K testing guidelines for heavy-textured soils.

Aims: To determine whether Colwell K is suitable for predicting plant-available K on loam- and clay-textured soil types developed from highly weathered soil parent materials in Western Australia (WA).

Methods: Nine soil K testing methods were used to determine plant-available K on 21 soil types with a wide range of properties collected from three depths on the northern, central and southern farmlands in WA.

Key results: Quartz and K-feldspars were the dominant minerals in all soils, while limited white mica (1–2%) was identified in less than 10% of samples. The amount of K extracted by silver thiourea was only about 70% of the amounts extracted by NaHCO₃ (Colwell K) and NH₄OAc. Soil non-exchangeable K extracted by nitric acid and sodium tetraphenyl borate were from similar K pools, while aqua regia K was 1–6 times higher than these values.

Conclusion: There was no systemic difference or proportional bias between NH₄OAc K and Colwell K, and both had good model performance (R² > 0.86) for total K uptake by wheat in a single growing season in a wide range of soils.

Implication: In this diverse range of soils formed from weathered parent materials, the reliance on exchangeable K for plant K uptake suggests that plant-available K will be vulnerable to rundown due to negative K balances.

背景： NaHCO ₃可提取土壤钾测试（Colwell K）是澳大利亚最常用的土壤钾测试方法，但钾测试指南对重质土壤的适用性仍存在不确定性。

目的：确定 Colwell K 是否适合预测西澳大利亚 (WA) 由高度风化的土壤母质发育而来的壤土和粘土质地土壤类型上的植物有效钾。

方法：采用九种土壤钾测试方法测定从西澳州北部、中部和南部农田三个深度收集的 21 种具有广泛特性的土壤类型的植物有效钾。

主要结果：石英和钾长石是所有土壤中的主要矿物，而在不到 10% 的样品中发现了有限的白云母 (1-2%)。_{硫脲银萃取K的量仅为NaHCO 3} (Colwell K)和NH ₄ OAc萃取量的约70% 。硝酸和四苯硼酸钠提取的土壤非交换性钾来自类似的钾库，而王水钾比这些值高1-6倍。

结论： NH ₄ OAc K 和 Colwell K之间不存在系统性差异或比例偏差，且 对于多种土壤中小麦单生长季总钾吸收量均具有良好的模型性能（ R ^{2 > 0.86）。}

含义：在由风化母质形成的多种土壤中，植物吸收钾对交换性钾的依赖表明，由于负钾平衡，植物可利用的钾很容易流失。