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Sorption and Desorption of Ammonium from Liquid Swine Waste in Soils

^a Dep. of Natural Resources & Environmental Design, North Carolina A&T State Univ., Greensboro, NC 27411
^b Dep. of Crop and Soil Science, 3111 Miller Plant Sciences Bldg., The Univ. of Georgia, Athens, GA 30602-7272
^c Dep. of Agronomy, Throckmorton Hall, Kansas State Univ., Manhattan, KS 66502-5501

View larger version (20K): [in a new window]   Fig. 1. Changes of sorption of NH4+ in Kennebec and Haynie soils with time. The two soils were exposed to the liquid swine waste (closed symbols) and the (NH4)2SO4 solutions (open symbols) at a soil/solution ratio of 1:10. The measured pH values of the liquid swine waste–soil mixture were 8.0 and 8.2 for Kennebec and Haynie soils, respectively. The pHs of the (NH4)2SO4–soil mixtures were adjusted to the same values as that of the corresponding waste-soil mixtures. Both solutions initially contained 495 mg NH4+–N L–1.

View larger version (20K): [in a new window]   Fig. 2. Langmuir sorption isotherms (solid lines) for NH4+ in the Kennebec and Haynie soils exposed to the liquid swine waste (solid symbols) and the (NH4)2SO4 solutions (open symbols). The dashed lines indicate a different stage of sorption. The initial NH4+ concentrations in both solutions varied from 75 to 2085 mg NH4+–N L–1. Ce and qe are the equilibrium concentrations of NH4+ in the supernatant (mg NH4+–N L–1) and sorbed in the soils (mg NH4+–N kg–1), respectively.

View larger version (20K): [in a new window]   Fig. 3. Percentage of sorbed NH4+ desorbed from NH4+–saturated Kennebec and Haynie soils after 2-h extraction with 0.01 M CaCl2 solution. NH4+ was initially sorbed onto the two soils by equilibrating them with the liquid swine waste (black bar) and the (NH4)2SO4 solutions (white bar) both containing 1075 mg NH4+–N L–1 for 72 h. Different letters indicate statistically significant difference (p < 0.05).

View larger version (17K): [in a new window]   Fig. 4. Ammonium remained sorbed in Kennebec and Haynie soils after sequential extraction with 0.01 M CaCl2 for 1 h. The soils were originally equilibrated with the liquid swine waste (closed symbols) and the (NH4)2SO4 solutions (open symbols) containing 1075 mg NH4+–N L–1 for 72 h.

View larger version (30K): [in a new window]   Fig. 5. (a) Ammonium sorption and (b) desorption in Kennebec (closed symbol) and Haynie (open symbol) soils exposed to the modified swine waste solutions containing varying dissolved organic C concentrations (circle symbols) and (NH4)2SO4 solutions (square symbols) for 24 h. The initial NH4+ concentration of all the solutions was 250 mg NH4+–N L–1. The pH and the concentrations of all the major cations and anions in the solutions matched that of the liquid swine waste shown in Table 2.

View larger version (29K): [in a new window]   Fig. 6. Ammonium sorption in Kennebec and Haynie soils exposed to the swine waste and the (NH4)2SO4 solutions at pH 4.0, 6.0, and 8.0 for 24 h. The initial NH4+ concentration of the solutions was 250 mg NH4+–N L–1. Different letters within each bar group indicate statistically significant difference (p < 0.05).