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Calcium and Magnesium Effects on Ammonia Adsorption by Soil Clays

^a Dep. of Agronomy, Purdue Univ., West Lafayette, IN 47907-1968
^b USDA-ARS, National Soil Erosion Research Lab., West Lafayette, IN 47907
^c Currently at the Univ. of Mississippi, duty station: U.S. Army Engineer Research and Development Center, 3909 Halls Ferry Rd., Vicksburg, MS 39180

View larger version (23K): [in a new window]   Fig. 1. Schematic diagram of ammonia distribution in the soil. M is metal exchangeable cation; OM—organic matter. Species not present in model clay system are marked in gray.

View larger version (27K): [in a new window]   Fig. 2. Change in the weight of the Mg-exchanged Fayette sample as experiment progresses. Dashed vertical lines indicate times at which spectra shown on Fig. 3 were taken.

View larger version (27K): [in a new window]   Fig. 3. Fourier transform infrared (FTIR) spectra of dry Fayette Mg sample before ammonia injection (a), immediately after ammonia injection (b), and 25 min after injection (c). Difference between Spectra c and a (d).

View larger version (19K): [in a new window]   Fig. 4. Correlation between amount of ammonium adsorbed and water displaced for Blount and Fayette soil clays.

View larger version (42K): [in a new window]   Fig. 5. Nitrogen retention in Blount and Fayette soil clays as a function of the exchangeable cation and relative humidity (RH). "Wet" samples were equilibrated at 90% RH, while "dry" were at 2% RH. Significant differences at 0.05 probability level are indicated by the different letters within the same measure: NH+4, NH3, and NH+4 + NH3.

View larger version (14K): [in a new window]   Fig. 6. Correlation between ammonium and water content for Blount and Fayette clays, and Fayette without organic matter (OM) at 2% relative humidity. Each point represents one sample.

View larger version (46K): [in a new window]   Fig. 7. Effect of organic matter (OM) removal on NH3 sorption by Fayette clay. "Wet" samples were equilibrated at 90% RH, while "dry" were at 2% RH. Significant differences at 0.05 probability level are indicated by the different letters within the same measure: NH+4, NH3, and NH+4 + NH3.

View larger version (16K): [in a new window]   Fig. 8. Correlation between ammonia and water content for Blount and Fayette soil clays at 2% and 90% relative humidity.