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 NaHCO 3 ‐soluble P, anion resin‐extractable P, P‐adsorption isotherms in 0.01 M CaCl 2 , 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 CaCl 2 ). 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 resinextractable 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.