Reactions of Ammonia With Soil. I

Sorption isotherms and heats of sorption of NH, gas on soils, Wyoming bentonite and silica gel were measured at 27 OC after preliminary drying at 22"-290 "C. Sorption of NMe, was also measured on some of the materials.Sorption on soils was not very sensitive to change in drying temperature, even though soil water content was markedly affected. Sorption on bentonite was dependent on drying temperature because this affected ease of lamellar separation.The results suggest that under the conditions employed, NH, sorption on the English soils studied is predominantly due to its protonation at pHdependent charge sites and partly to co-ordination with exchangeable Mg or Ca (but not Na or K). Sorption through mechanisms involving hydrogen bonding is apparently negligible.

show abstract

REACTIONS OF AMMONIA WITH SOIL, III SORPTION OF AQUEOUS NH₃ BY HOMOIONIC SOIL CLAYS

Ashworth

Pyman

1979

Journal of Soil Science

Self Cite

View full text Add to dashboard Cite

Homoionic clay suspensions were equilibrated at 25°C with aqueous NH, (0.01 to 0.30 M) by agitating for several days. Using clays extracted from three different soils, sorption of NH,, measured by titntion, followed the order Na > Ca > NH,-chy. The difference in NH, sorption between Na-clay and NH,clay was matched by an increase in Na' ion conantration in the aqueous phase of suspensions of Na-clay treated with NH,, but there was no such effect with Ca-clay.Sorption of NH, on NH,-clay in aqueous suspendon is considered due to proton donation at sites of pHdependent charge, and the additional sorption on Na-clay to dir placement of Na' by NHf ions. The additional aorption on Ca-clay r e m s largely due to co-ordination of Ca" ions with molecular NH , . Exchangeable cations affect NH , wrption differently when an aqueous phase ia present than when dried homoionic materials are treated with NH, gas. Intraluction LARGE-SCALEuse of ammonia as a fertiliser began in the 1930s when it was added to irrigation water in Californian orchards. Jenny et ul. (1945) studied sorption of aqueous NH, on Californian soils, and the availability of sorbed NH3 to plants and nitrifying bacteria.Since the 1950s, most NH, has been injected into soil in bands, either as aqueous or, especially in the U.S.A., as anhydrous NH3. Almost all subsequent nsearch (see McVickar et uL, 1966, for reviews) has involved using NH, gas and dried soil or clay. However, studies involving an aqueous phase have an obvious relevance to practical agriculture, and the various mechanisms proposed for NH3 sorption on dried materials might have different relative importance under aqueous con& tions.Various workers, using dried homoionic soils and clays, have studied the effects on NH3 sorption of altering the exchangeable cation. Some (Mortland et uf., 1963;James and Harward, 1964; Russell, 1965;Mortland, 1968) have emphasised the importance of sorption mechanisms actually involving exchangeable cations; previous papers in this series (Ashworth, 1973 and1978) have drawn attention to the contribution to overall sorption due to reaction of NH, at sites of pHdependent charge.

show abstract

Reactions of Ammonia With Soil. I

Cited by 6 publications

References 22 publications

Nitrogen

Nitrogen