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ARS Home » Midwest Area » West Lafayette, Indiana » National Soil Erosion Research Laboratory » Research » Publications at this Location » Publication #178438
Title: CALCIUM AND MAGNESIUM EFFECTS ON AMMONIA ADSORPTION BY SOIL CLAYS

Author
item DONTSOVA, K - PURDUE UNIVERSITY
item Norton, Lloyd
item JOHNSTON, C - PURDUE UNIVERSITY

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/21/2005
Publication Date: 8/30/2005
Citation: Dontsova, K.M., Norton, L.D., Johnston, C.T. 2005. Calcium and magnesium effects on ammonia adsorption by soil clays. Soil Science Society of America Journal. 69:1225-1232(2005).

Interpretive Summary: Nitrogen is one of the most commonly applied plant nutrients and often is applied as anhydrous ammonia. Its nitrogen use efficiency is controlled by the ability of the soil to hold it and release it to plants as needed. Loss of nitrogen is a major problem to producers and can result in adverse water quality through natural processes. We conducted a study in the laboratory to measure how much ammonia could be held by clays at different moisture content, adsorbed cations and organic matter from two common Midwest USA corn-belt soils. We found through spectroscopic techniques that ninety percent more ammonia was held at high moisture content than at low despite a decrease in the amount of ammonium adsorbed. We also found that magnesium clays held significantly more nitrogen in both ammonia and ammonium forms at high moisture content than the same calcium rich clay. A soil from the western corn-belt held more nitrogen that one from the eastern corn-belt because of the nature of the clay type. Removal of organic matter caused the clays to hold more ammonia. The impact of this research is that better guidelines can be developed for application of ammonia to soils to improve nitrogen use efficiency knowing soil conditions.

Technical Abstract: Anhydrous ammonia is a widely used nitrogen fertilizer and its interactions with soils and soil clays play an important role in its environmental fate. This study was conducted to determine the quantity and forms of ammonia adsorbed by clay-sized fractions of soils as a function of water content, exchangeable cation, and organic matter. Fourier transform infrared spectroscopy was used to evaluate in situ the mechanisms of interaction of H2O, NH3 and NH4+ with the clay size fractions of a Blount loam (fine, illitic, mesic Aeric Epiaqualfs) and a Fayette silty clay loam (fine-silty, mixed, mesic, superactive Typic Hapludalfs). Due to NH3 dissolution in adsorbed water more total N was sorbed at high (90%) than at low (2%) relative humidity despite decrease in the amount of NH4+ sorbed. At high relative humidity, the amount of NH4+, NH3 and total N increased by 12 - 23% on the Mg-exchanged compared to the Ca-exchanged soil clays. Of the two soil clays, the smectitic sample (Fayette) sorbed more of both N species than the illitic sample (Blount). Samples with organic matter removed adsorbed significantly more ammonia than untreated samples. The mechanism suggested for ammonia sorption by soil clays is a combination of protonation on water associated with metal cations, coordination to the exchangeable cations and dissolution in pore water. Soil clays can retain significant amounts of ammonium in excess of the CEC and out of competition for exchange sites. Dissolved NH3 constituted the majority of N adsorbed by the sample at high relative humidity, which is typical of field conditions.