Farmers and crop advisors rely on soil testing to evaluate soil nutrient status and to plan fertilizer applications. Plants require at least 14 essential plant nutrients, which can be classified into macro-(N, P, K, S, Ca, Mg and Na) and micronutrients (Cu, Zn, Mn, B, Mo, Si, Ni, and Cl) (Kirkby, 2012). Several different soil testing methods have been developed to estimate the capability of soil to provide nutrients for crops, without clear consensus on which method to apply (Hochmuth & Hanlon, 2010;Stockdale et al., 2002;Wuenscher et al., 2015). Several regional soil testing methods have been applied for decades to identify crop-limiting factors and to guide fertilizer applications (Berger & Truog, 1939;Spurway, 1948;Vuorinen & Mäkitie, 1955). Soil testing is also used to monitor the build-up and draw-down of