Evaluation of Soil Test Phosphorus Extractants in Idaho Soils

Abstract

Core Ideas Bray‐1, Mehlich‐3, Haney–Haney–Hossner–Arnold, and Olsen‐P were compared on primarily alkaline calcareous soils. Mehlich‐3 was correlated with the Olsen‐P extractant regardless of pH or inorganic C content. Soil P testing is critical to ensure the accuracy of fertilizer recommendations and to optimize crop yield while minimizing negative environmental consequences. Olsen‐P is the most commonly used soil P test for alkaline calcareous soils found in Idaho and the western United States. The Bray‐1 test is commonly used in the Pacific Northwest on neutral to acidic soils but underestimates P in alkaline calcareous soils. Mehlich‐3 has been evaluated throughout various regions in the United States. Few data evaluating Mehlich‐3 exist for soils in the western United States. Additionally, the comparatively newly developed Haney–Haney–Hossner–Arnold (H3A) test, a component of the soil health tool, has not been widely evaluated on alkaline calcareous soils. Soil samples from the 0‐ to 30‐cm depth were collected from agricultural fields throughout Idaho and analyzed with Bray‐1, H3A, Mehlich‐3, and Olsen‐P extractants. The results indicate that Olsen‐P was correlated with Mehlich‐3, whereas Bray‐1 and H3A were not correlated with Olsen‐P. Both Bray‐1 and H3A resulted in lower values of extractable P than the Olsen‐P test, whereas Mehlich‐3 resulted in greater values. A threshold point in CaCO 3 (i.e., inorganic C) of 6.7 and 5.1 mg kg ‐1 for the Bray‐1 and H3A was obtained, respectively, which indicated that inorganic C concentrations at or above these levels resulted in a reduction in extractable soil P. Thus Mehlich‐3 could be evaluated for use in alkaline calcareous soils, whereas Bray‐1 and H3A have notable issues that would limit their applicability.