Objectives The fixation of phosphorus (P) is a vital reason for low fertilizer effectiveness. Therefore, mobility of different phosphate sources under different application methods was compared in this paper, to provide reference for phosphorus fertilizer management.
Methods A chamber simulation experiment was carried out at (27 ± 1.0)℃, using calcareous clayey and loamy soils as tested materials. The amount of applied P was 0.0581 g/column in loamy soil and 0.0594 g/column in clayey soil. The tested P sources included polyphosphate, pyrophosphate and urea phosphate, which were all applied once on the surface and evenly divided into four parts and applied with watering in 7 days intervals (split application). Soil columns without adding P were used as the controls. After 28 days of treatment, the soil columns were immediately frozen and solidified at ‒80℃, then sliced in every 5 mm within the first 0‒100 mm depth and in every 20 mm afterwards. The contents of water soluble P and Olsen-P in each layer of soil were determined.
Results Under single application, the down movement of P from polyphosphate, pyrophosphate and urea phosphate were 90, 60 and 50 mm in loamy soil, and 80, 70 and 60 mm in clayey soil, respectively. Under split application, the down movement of P from polyphosphate in loamy soil (95 mm) was 46.2% and 35.7% higher than those from urea phosphate (65 mm) and pyrophosphate (70 mm), and that from polyphosphate in clayey soil (90 mm) was 28.6% and 20.0% higher than those from urea phosphate (70 mm) and pyrophosphate (75 mm), respectively. In loamy soil, the half-depth of soil, which was the down distance with the water soluble P content half reduced, for polyphosphate, pyrophosphate and urea phosphate under single application were 15.1 mm, 11.4 mm and 10.5 mm, under split application were 20.0 mm, 14.4 mm and 14.3 mm; in clayey soil, the half-distance of polyphosphate, pyrophosphate and urea phosphate under single application were 17.7 mm, 15.8 mm and 14.8 mm, and under split application were 51.3 mm, 27.1 mm and 41.4 mm. Correlation analysis results showed that whether single or split application, the Olsen-P contents increased more in clayey soil than in loamy soil with the increase of water soluble P content. At the same water soluble P content, the discrepancy of Olsen-P contents between the loamy soil and clayey soil became narrow under split application of polyphosphate; the Olsen-P content in both soils was agreeable for pyrophosphate; the Olsen-P content increased more in clayey soil under single application of urea phosphate and opposite under split application.
Conclusions In the calcareous loamy and clayey soil, the vertical downward movement distance of P is in order of polyphosphate > pyrophosphate > urea phosphate under both single and split application. And the mobility and availability of P in the soil columns are higher under split application than under single application. At the same water-P content, the availability of P in clayey soil is higher than that in loamy soil, and the effect of improving P availability in clayey soil is better than that in loamy soil under split application.
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