Relating High Soil Test Phosphorus Concentrations to Plant Phosphorus Uptake

Abstract

Abstract The median P soil‐test concentration in Michigan has increased above the point at which a yield response is expected from fertilizer P application. This study was conducted to determine whether several soil‐P extractants reflect plant P uptake under high residual soil P conditions and to estimate the reduction in soil‐test P concentration as a result of crop removal. Initial P concentrations of the surface 0‐ to 15‐cm layer of ten Michigan soils were determined with Bray‐Kurtz P1, Bray‐Kurtz P2, Olsen, and anion‐exchange resin (AER) as extracting solutions. Ten consecutive crops were grown for 5 wk each on each soil. Phosphorus uptake by each crop was calculated from yield and composition. Linear correlation coefficients among the Bray‐Kurtz P1 and P2, Olsen P and AER P methods ranged from 0.79 to 0.99. Linear correlation coefficients between initial test P concentrations and cumulative P uptake were from 0.40 to 0.74. The highest correlation was with the Olsen extractant and the lowest was with Bray‐Kurtz P1 (1:20). A comparison of change in extracted soil‐P content with P uptake showed that the Bray‐Kurtz P1 extractant at a soil/solution ratio of 1:20 and the Bray‐Kurtz P2 extractant most closely estimated the magnitude of P removed by plants. On the cultivated soils, there was a change of 0.13 to 0.31 mg P kg −1 soil in the Bray‐Kurtz P1 soil test for each mg P kg −1 soil removed by plants.