Evaluating buffer methods for determinining lime requirement on acidified agricultural soils of the Palouse

Authors: MCFARLAND, CAROL - Washington State University; SANTOSH, SHIWAKOTI - Washington State University; CARPENTER-BOGGS, LYNNE - Washington State University; SCHROEDER, KURT - University Of Idaho; BROWN, TABITHA - Idaho Department Of Water Resources; Huggins, David

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/21/2020
Publication Date: 6/5/2020
Citation: McFarland, C., Santosh, S., Carpenter-Boggs, L., Schroeder, K., Brown, T., Huggins, D.R. 2020. Evaluating buffer methods for determining lime requirement on acidified agricultural soils of the Palouse. Soil Science Society of America Journal. https://doi.org/10.1002/saj2.20111.
DOI: https://doi.org/10.1002/saj2.20111

Interpretive Summary: Soils in the Palouse region of Eastern Washington and Northern Idaho are acidifying and acid soils negatively impact crop yields. Lime applications can address the problem, but calibrated soil buffer tests, used to determine lime requirements, are lacking. We evaluated six different buffer tests and determined which ones can estimate optimal lime requirements for Palouse agricultural soils. We concluded the following: (1) The Modified Mehlich, Woodruff 6 and Woodruff buffers were the best buffer tests for determining lime requirements for Palouse soils; (2) The two buffer tests that are currently used by regional laboratories are not well suited and should be replaced; and (3) soil tests of organic matter and either extractable aluminum or pH in combination were also useful for estimating lime requirements. These results will be useful for commercial soil laboratories, farmers, NRCS and scientists interested in determining lime requirements to correct acid soil conditions in the Palouse region.

Technical Abstract: Ameliorating acidified soils in the Palouse region of Eastern Washington and Northern Idaho is of increasing concern. Soil buffer tests can provide lime requirement estimates to address acid soils; however, locally calibrated tests are lacking. Our objective was to evaluate buffer tests and determine which can produce optimal lime requirement estimates for Palouse agricultural soils. Samples from ten regionally dominant agricultural soils (initial pH < 5.33) were assessed for pH changes after incubation with nine levels of CaCO3, for 90 days under laboratory conditions. Achieving a target pH of 6 in the top 15 cm of the soil profile required 3.36 to 8.36 Mg ha-1 of CaCO3. Laboratory incubations were compared with six buffer tests: Shoemaker, McLean, and Pratt (SMP), Adams and Evans, Woodruff, and Woodruff 6, Sikora and Modified Mehlich (MM). The SMP (R2=0.47) and Adams and Evans (R2=0.56) demonstrated the lowest correlation with observed lime requirement, and are not recommended for use on Palouse soils. The Modified Mehlich (R2=0.90), Woodruff 6 (R2=0.78) and Woodruff (R2=0.75) buffers produced the strongest correlation between test estimates and the lime requirement determined by laboratory incubation. Soil test variables of organic matter (OM) and either KCl extractable aluminum (KCl Al) or pH, were also predictive of lime requirement (R2=0.72). The recommendation from this study is to assess lime requirement on Palouse soils using the Modified Mehlich test or to utilize soil analytical results and compute lime requirement from OM and KCl Al or pH.