The Absorption of Phosphorus from Phosphate Fertilizers Applied to Established Meadows: III. Effect of Phosphorus Source and Placement and of Meadow Composition

Three experiments were conducted to determine the absorption of phosphorus from concentrated superphosphate and calcium metaphosphate when applied to established meadows. They were located on Ida silt loam, a loess derived calcareous (pH 7.8) soil in western Iowa; Seymour silt loam, a loess derived acid (pH 5.8) soil in southern Iowa; and Floyd loam, a glaciated acid (pH 5.6) soil in northeastern Iowa. The differential phosphate treatments supplied 40 pounds of P₂O₅ per acre as concentrated superphosphate and <10 and <40 mesh calcium metaphosphate. Each phosphate source was applied broadcast or drilled in rows 7 inches apart and about an inch deep to compare placement. It was found that either broadcasting or drilling the phosphate fertilizers studied was an effective means of supplying additional phosphorus to established meadows; however, the drilling operation appeared to decrease the forage yields slightly at all three locations. In addition, the plant absorption data for phosphorus showed that broadcasting was more effective than drilling as a method of applying calcium metaphosphate. The finer <40 mesh calcium metaphosphate supplied a greater percentage of the plant phosphorus than did the <10 mesh material. The data indicate that superphosphate was more readily available to plants than was calcium metaphosphate, and that it might be preferred on extremely phosphorus-deficient soils. Otherwise it seems that calcium metaphosphate might be used on a phosphorus equivalent basis. In general, the legumes derived a greater percentage of their phosphorus from the fertilizer than did the associated grass, especially in case of the first hay cutting and with calcium metaphosphate. These differences were not as consistent in the second cutting and in case of superphosphate.