Effect of Fertilizer Phosphorus Placement on the Availability of Phosphorus

Abstract Greenhouse studies were conducted with oats ( Avena sativa L.) to determine why band applications of fertilizer P are often more effective than broadcast applications of equal rates. Phosphorus fertilizer solutions tagged with 32 P were applied to the soil with different spacing distances between solution application points. All the P fertilizer was applied at approximately equal distance from oat seeds (48 mm), while application points were spaced 0, 16, 32, and 48 mm from one another. Investigations were conducted using two soils, a Uly silt loam subsoil (fine‐silty, mixed, mesic Typic Haplustolls) with soil pH 8.4, a calcium carbonate equivalent of 4.2%, and 1.2 mg kg −1 NaHCO 3 ‐extractable P; and a Thurman loamy fine sand (sandy, mixed, mesic Udorthentic Haplustills) with soil pH 5.9 and 11 mg kg −1 Bray and Kurtz no. 1‐extractable P. On the high pH calcareous silt loam soil, yield and P uptake were greatest when application points were spaced far apart. However, on the acid loamy fine sand, no relationship was found between the spacing of the application points and P uptake. It was concluded that on the loamy fine sand, movement of P from a single spot increased the probability that root‐fertilizer contact would occur, whereas no such movement occurred in the silt loam. The amount of P uptake by oats was nearly proportional to the volume of soil containing the applied P fertilizer. Apparently, the early beneficial effects of banding are obtained mainly from placing all of the fertilizer where contact by active roots is likely, rather than from any increase in availability that may be obtained from decreased soil‐fertilizer contact associated with banding. If this is the case, then soils in which P is relatively immobile, most efficient use of P fertilizer will be made by the young plants if the fertilizer is mixed thoroughly with the soil near the seed into which a high concentration of roots will grow.