Comparison of Bray‐1 and Mehlich‐3 extraction of P and K in Wisconsin silt loam soils

Abstract

AbstractPhosphorous (P) and potassium (K) fertilizer rate recommendations are based on soil nutrient concentrations, which can be measured using a variety of lab methods. In Wisconsin, Bray‐1 extractant is used to measure soil test P (STP) and soil test K (STK), while most neighboring states measure STP and STK using Mehlich‐3 soil test extractant. This research aims to quantify the relationship between Bray‐1 and Mehlich‐3 extraction methods for both STP and STK for silt‐loam soils in southern Wisconsin. Soil samples were collected from three fields in November 2021. STK and soil test phosphorus STP were measured using both Bray‐1 and Mehlich‐3 extraction methods. The relationship between Bray‐1 and Mehlich‐3 extractants was quantified using linear regression. Soil test phosphorus as measured using Bray‐1 extractant was linearly related to STP as measured using Mehlich‐3 extractant (p < 0.001; Adj. R2 = 0.97), and the relationship between STK results from Bray‐1 extraction and STK results from Mehlich‐3 extraction was also linear (p < 0.001; Adj. R2 = 0.91). For the same soil samples, Mehlich‐3 extractant removed slightly more P and K as compared to Bray‐1 extractant. Due to the strong linear relationship between Mehlich‐3 and Bray‐1 extractants, simple regressions can be used to estimate Bray‐1 STP or STK from a soil test report that was generated using Mehlich‐3 lab methods, and vice versa, on WI silt‐loam soils.