Lime effects on phosphorus availability in a calcareous soil

Crop yields are sometimes reduced on irrigated calcareous soils with elevated lime concentrations. This study was conducted to determine the influence of lime on P availability. The effects of acid-equivalent lime concentrations and P fertilization rates on NaHCO3-soluble P, anion resin-extractable P, P-adsorption isotherms in 0.01 M CaCl2, and P uptake by sudangrass [Sorghum bicolor (L.) Moench] and potato (Solanum tuberosum L.) were investigated in the greenhouse on soil samples from the Portneuf silt loam (coarse-silty, mixed, mesic Durixerollic Calciorthid). Plant P uptake was increased by P fertilization and decreased by increasing lime concentration. Phosphorus uptake was curvilinearly related to solution P (extracted by 0.01 M CaCl2). Solution P concentrations increased linearly as the resin-extractable P/equilibrium buffer capacity (EBC) ratio increased, where EBC is the slope of the P-adsorption isotherm at the indigenous equilibrium P concentration. The EBC increased as the lime concentration increased. Phosphorus applications increased solution P and resin-extractable P and decreased EBC within a given lime concentration. These data indicate that the soil-test P concentration or P fertilization rate should increase as the lime concentration increases to provide the same degree of P availability and plant P uptake in this calcareous soil