Updated Lime Requirement Recommendations for Oregon

The Oregon State University Soil Fertility Program has completed a formal evaluation of the Sikora buffer to replace the SMP buffer for estimating lime requirement in Oregon. Twenty-four acidic soils from Oregon were tested for actual lime requirement using a lab incubation of lime and soils. The actual amount of lime needed to reach pH targets of 5.6, 6.0, and 6.4 was highly correlated to the SMP buffer (r2 = 0.91-0.93) and the Sikora buffer pH (r2 = 0.91-0.93). These correlations are the basis for new updated lime recommendations for both Sikora and SMP buffer pH methods (Table 1) and will be used to update OSU extension guides containing lime recommendations. The new SMP recommendations are included for the time being for the remaining labs still using the SMP method, but may be phased out over time as more labs switch to Sikora. We thank the Oregon Tall Fescue Commission for providing the necessary support to complete this project.