contents, and pH. Analytical methods used to assess the soilcharacteristics are reported in Table 1. Briefly (Figueiredo et al.,2013b), the determination for non-exchangeable NH4+–N wasbased on 1.0 g soil (<1.49 mm) treated with an alkaline potassiumhypobromite (KOBr–KOH) solution to remove exchangeable NH4+and soil organic N. The clear supernatant liquid was decanted anddiscarded, while the residue was transferred into polyethylenecentrifuge tubes and washed with 0.5 M KCl to remove residualexchangeable NH4+. This operation was repeated three times.Finally, the residue was treated with a 5 M HF–1 M HCl solution andplaced in an orbital shaker for 24 h to disintegrate the clay mineralscontaining the “fixed” NH4+. The non-exchangeable NH4+ releasedby HF–HCl was then determined by spectrometry at 660 nm.Floodwater samples were directlyfiltered and analyzed forsoluble N content and pH using the same procedures as reported inTable 1.
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