Comparison of Soil‐Test Extractants for Potassium, Calcium, Magnesium, Sulfur, and Micronutrients in Idaho Soils

Abstract

Core Ideas Multinutrient extractants were correlated to standard tests on alkaline calcareous soils For the tested nutrients Mehlich‐3 generally extracted greater and H3A less than the common tests used in the Western United States Mehlich‐3 extracted large amounts of Ca when inorganic‐C as CaCO3 was greater than 3.3 g kg−1 resulting in poor correlation with the ammonium acetate test Soil fertility and nutrient management programs across Idaho and the western United States should consider the effective comparison of various extractants for nutrient analyses. Common extractants for K, Ca, Mg, S, and micronutrients (Zn, Cu, Mn, Fe, B, Na) vary (e.g., ammonium acetate [AA], Olsen, etc.). The desire to develop effective correlation equations among common tests in the region and those of multinutrient extractants used or proposed in other geographical regions (i.e., Mehlich‐3 [M‐3] and Haney, Haney, Hossner, Arnold [H3A]) has increased due to the interest in nutrient management planning and in relation to soil health measurements. To investigate these multinutrient tests, 46 primarily alkaline soils were sampled from the 0‐ to 30‐cm depth in agricultural fields in Idaho. Linear regressions between AA and Olsen K and both M‐3 and H3A resulted in a significant positive fit (R2 = 0.69–0.90). Notable issues with increased Ca concentrations occurred in soils with large amounts of inorganic C. Removal of these samples improved the relationship between standard and multinutrient soil tests. Specific micronutrient regressions were problematic when both alkaline and acidic soils were analyzed but improved when separated. Mehlich‐3 and H3A extractants were generally well correlated, with the exceptions noted above, to common extractants used in western soils. Thus, this research provides specific correlation equations that could be used for comparison among tests as well as provides evidence of the potential suitability of multinutrient extractants in the region.