Evaluation of Soil Test Phosphorus Extractants in Idaho Soils

Abstract

© Soil Science Society of America. This is an open access article distributed under the CC BY license (https://creativecommons.org/licenses/by/4.0). 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 CaCO3 (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.