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Fluid Journal : Winter 2016
MAP-, and (DAP)-derived P in a highly calcareous Australian soil and two mildly calcareous soils from the U.S. (Idaho and Western Kansas). Methodology Soils. A five-week laboratory-based incubation experiment was set up that used three soils containing various amounts of free calcium carbonate [CaC0 3 ] (none had a history of being fertilized): 1) a mildly calcareous Entisol soil collected from southwest Idaho, 2) a mildly calcareous Inceptisol soil collected from western Kansas, and 3) a highly calcareous Inceptisol soil collected from South Australia. The Kansas soil pH was 8.34 and soil texture a silt loam (SiL), with an effective CaC0 3 of 7.7 % total P 625 mg kg- 1 , and Mehlich P 15.6 mg kg- 1 . The Idaho soil pH was 8.02 and soil texture a sandy loam (SL), effective CaC0 3 10.9 0 /0, total P 468 mg kg- 1 , and Mehlich P 31.8 mg kg- 1 . The Australian soil pH was 8.63, soil texture an SL, effective CaC03 83.3 0 /0, total P 681 mg Kg-1, and Mehlich P 39.1 mg kg- 1 . Fertilizer. Three P fertilizer sources were chosen for incubation: monoammonium phosphate (MAP), di-ammonium phosphate (DAP), and ammonium polyphosphate (APP). Monoammonium phosphate and DAP were added in granular form and APP was added as the fluid P source. The granular or fluid fertilizer containing an equivalent amount of P, approximately 9.8 mg P, and the nitrogen (N) balanced using urea, was placed in the center of petri dishes filled with one of the 3 soils at a moisture content equivalent to 60 percent of its maximum water-holding ca pa city. Treatments totaled 4, including a control treatment. The 5 replicates of each treatment on the 3 soils were covered and incubated in petri dishes for five weeks at 250C. Soil samples. After five weeks, the soil was collected in 4 concentric rings from the central point of application: 0-7.5 mm, 7.5-13.75 mm, 13.75-25 mm, and 25-43.5 mm. The soil samples were analyzed for total P using aqua-regia digestion, pH (1: 10) in water, resin extractable P using Meyers et al.  for P extraction. P determination was completed using the Murphy Riley Methods. P mass. The Percent P added was calculated by dividing the net increase of the total P mass for each dish ring 5 KS pH Figure 1. Soil pH: Kansas calcareous soil 1:J 0.0 0 KS Percent PAdded :mo.oo a "'U . 11I.00 "'U . 0-15 ... "'U C tiO_ a.. .15-13..15 ... .... :c . 40.00 . 13.15-25 ... u - . a.. . :l5-43..5 ... 20_ 0.00 IMP nAP APP P T..It:db.R:II'" Figure 2. Kansas Percent P Added: Significantly more P added remained at the point of application for the DAP treatment than for APP treatment. For the second section] there was significantly more P fertilizer movement for APP than either granular treatment. Table 1. P XANES data - Kansas Soil Soil P species (oÆ>) Section 1: 0-7.5 mm Treatment pH Calcium Alumina- Strengite Reduced Phosphate Adsorbed P Chi-Square Control 8.68 72.1 27.9 -- 0.020 MAP 8.02 54.5 -- 45.5 0.006 DAP 8.43 79.2 20.8 -- 0.030 APP 7.70 47.5 22.1 30.4 0.010 The Fluid Journal Winter 2016