A proposed mechanism for the volatilization of ammonia from fertilized neutral to alkaline soils

Ammonia volatilization from five soils, ranging in clay content from 7,6 to 49,9%, were determined after pH values of the soils were adjusted to 8,0. Ammonium sulphate, limestone ammonium nitrate, urea, monoammonium phosphate and diammonium phosphate were applied on the soil surface at levels equivalent to 0,15, 30, 60,120 and 240 kg N ha−1. After a contact period of three days ammonia losses were determined. Ammonia was lost from all soils under all treatments, losses increasing with increasing levels of application. Loss of ammonia from the various fertilizers was ranked as follows: LAN < MAP < (NH4)2)SO4 < DAP < urea. Surprisingly, ammonia losses increased with an increase in clay content or cation exchange capacity of the soil. The apparently anomalous role of the cation exchange complex of the soils to ammonia volatilization can be ascribed to the buffer capacity of the soils. An explanation for the volatilization mechanism is proposed. S. Afr. J. Plant Soil 1986, 3: 31–34