Comparison of four phosphorus extraction methods on three acid southeastern soils

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Abstract
Phosphorus extractants have not been tested extensively in the Southeast. An experiment was carried out to compare four P extractant methods using samples from a field P‐K factorial experiment with soybeans (Glycine max (L.) Merr.) at three locations in Georgia over four years. There were five P rates ranging from none to 80 kg ha‐1. Soils and plant tissue were sampled at mid‐summer and yields were recorded. The four P extractants compared were Olsen, Mehlich 1, Mehlich 2, and Bray 1. Quadratic regressions for soil P versus plant P and P rates were not significant compared to linear regressions. There were no significant yield responses to P. All extractants except Olsen were similar in their response to added fertilizer P as measured by linear r2 values. Olsen P gave lower linear r2 values both with P rate and with plant P. Mehlich 1 values were highly correlated with Mehlich 2 (0.94**) and Bray 1 (0.96**). Mehlich 2 and Bray 1 gave nearly the same soil P values with linear regressions of slope of 1.0 and low intercepts. Results from these experiments show that Mehlich 1, Mehlich 2, or Bray 1 could be used successfully on these soils, but that Olsen should be avoided.