Disposition of Fertilizer Phosphorus Applied to Winter Wheat

The disposition of fall‐applied fertilizer P (30 kg P ha −1 ) to winter wheat ( Triticum aestivum L.) on four Southern Plains soils was investigated over a 4‐yr period under field conditions, using 32 P as a tracer. Wheat was harvested 70 d after planting and P fertilization. An average increase in wheat dry‐matter yield (0.86‐1.94 Mg ha −1 ) and Bray‐1 P content of 0‐ 50‐mm surface soil (8.4‐34.4 mg kg −1 ) was observed following each fertilizer P application over the 4 yr. The major proportion of applied fertilizer P at wheat harvest remained in the soil as inorganic P (60‐76%) with little conversion to organic P (8‐15%). The proportion as Bray‐1 P ranged from 17 to 51%, decreasing with an increase in P sorption capacity of the soil. With consecutive fertilizer applications the proportion of fertilizer P as Bray‐1 P increased. Little movement of fertilizer P was observed below the 50‐mm depth (3‐7%). Recovery of fertilizer P by winter wheat decreased with consecutive fertilizer applications, ranging from 23 to 9% of that applied. The recovery was inversely related to the residual Bray‐1 P content of surface soil (Bray‐1 P content prior to each fertilizer application). Thus, although dry‐matter yield of winter wheat increased with consecutive fertilizer applications, fertilizer P recovery decreased as residual P made an increasing contribution to uptake of P by winter wheat. Consideration of residual soil P levels may, thus, reduce costly maintenance fertilizer P applications.