Soil Permeability in an Ammonium and Phosphorus Application Zone
- R. Myers and
- S. J. Thien
Soil organic matter plays a primary role in the development and maintenance of aggregate stability necessary for good soil permeability. Studies showing that some N and P fertilizers dissolve soil organic matter raise questions about effects these fertilizers have on permeability. In this work, filtration rates (FR) in Kennebec silt loam (fine-silty, mixed, mesic Cumulic Hapludoll) were monitored after addition of NH4OH and NH4 phosphates to determine whether organic-matter dissolution occurring after fertilizer application affected soil permeability. Twenty combinations of NH4OH and either monoammonium phosphate (MAP) or triammonium pyrophosphate (TPP) were applied to soil columns 70 mm in diameter. The columns were incubated for 0.5, 1, 2, 4, 8, 16, or 32 d at 35 °C. Soil from the application zone was removed from the column and analyzed. Increasing NH4OH levels usually decreased FR. Compared with FR when no NH4OH was applied, NH4OH levels of 1500, 3000, and 6000 mg kg−1 reduced FR 20, 30, and 33%, respectively. Treatments including P had variable effects on permeability. With the following P sources and levels (mg P kg−1): 0 P, 300 MAP-P, 300 TPP-P, 600 MAP-P, and 600 TPP-P, average FR (1 + log mL min−1) were 2.13, 1.99, 1.88, 2.25, and 1.72, respectively. The NH4OH and P treatments dissolved between 0.1 and 4.8% of the total organic matter in the analyzed samples. Increases in dissolved organic matter were highly correlated with decreases in FR (R2 = 0.78-0.98). Increased dissolution of organic matter increased soil dispersion and lowered permeability in the application zone.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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