RESIDUAL EFFECTS OF FERTILIZER PHOSPHORUS AS MEASURED BY CROP YIELDS, PHOSPHORUS UPTAKE, AND SOIL ANALYSIS

Monocalcium phosphate was broadcast at 0, 50, 100, and 200 kg P/ha to a calcareous soil, very low in NaHCO 3 -extractable P. Wheat (Triticum aestivum cv. Selkirk) and flax (Linum usitatissimum cv. Marine) were seeded in the 1st yr and barley (Hordeum vulgare cv. Montcalm) and flax were alternated in 3 subsequent yr. Subplot treatments consisted of 0, 5, 10, 20 and 40 kg P/ha applied as monoammonium phosphate with the seed. Wheat and barley responded well to broadcast or seed-drilled P. The latter was the most effective method of application; this was apparent even on plots receiving large amounts of broadcast P. In contrast, flax was not responsive to newly applied P, and yields decreased with application of seed-drilled P in combination with large amounts broadcast. The solubility of P in the untreated soil was between that of octacalcium phosphate (OCP) and hydroxyapatite (HA). The solubility of P in the treated soils was greater than in the untreated soils for the duration of the sampling period (3 yr) and was slightly less than that of OCP for the 50 kg/ha treatments, about that of OCP for the 100 kg P/ha treatment and greater than that of OCP for the 200 kg P/ha treatment. These studies indicate that the reaction product most likely governing the solution concentration of P was OCP.