Ammonium Adsorption and Desorption in Sandy Soils
2000
Wang, F. L. | Alva, A. K.
Leaching of fertilizer N in sandy soils is both an agricultural and environmental concern and depends, in part, on the N holding capacity of the soils in the vadose zone. We examined NH₄ adsorption and desorption in surface (0–30 cm) and subsurface (30–60 cm) samples of Wabasso (sandy, siliceous, hyperthermic Alfic Alaquod) and Candler (uncoated hyperthermic, Typic Quartzipsamment) sands using a batch technique. Samples of a 90- to 100-cm depth horizon of the Wabasso sand were also used in the study. The NH₄ quantity–intensity (Q/I) relations showed that the potential buffering capacity (PBC) of the soils ranged from 0.26 (Wabasso, 30–60 cm depth) to 3.9 (Wabasso, 90–100 cm depth) cmolc kg⁻¹ M ⁻¹/² Labile NH₄, as determined from the Q/I, was 4.9 × 10⁻³ (Candler, subsurface) to 13.8 × 10⁻³ (Wabasso, surface) cmolc kg⁻¹ Positive linear relationships were observed between organic C content and Q/I plot parameters (potential NH₄ buffering capacity and labile NH₄) of all soil samples except in the Wabasso 90- to 100-cm depth horizon. Although NH₄ adsorption capacity of the surface soils was greater than that of the subsurface soils, desorption was greater from the former soils than that from the latter. This study clearly demonstrated that the potential NH₄ buffering capacity and labile NH₄ for the sandy soils studied were much lower than those for clay and silt loam soils.
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