Ammonia Volatilization from Surface‐Applied Urea: Effect of Hydrogen Ion Buffering Capacity

Abstract

AbstractThe influence of soil pH and soil cation exchange capacity on ammonia volatilization from surface applied ammoniacal nitrogen has been reported in previous studies. Since the hydrolysis of ureacontaining N fertilizers causes an increase in alkalinity, a soil's inherent H+ buffering capacity (defined as the soil's total acidity, comprised of exchangeable acidity plus non‐exchangeable, titratable acidity), should exert a dominant influence on the maximum soil pH at the site of urea fertilizer application. The objective of this study was to demonstrate the importance of a soil's H+ buffering capacity in affecting NH3 volatilization from surface‐applied urea. The H+ buffering capacity of two soils was increased by adding hydroxy‐Al polymers to one soil, and weak and strong acid cation exchange resins to the other soil. Care was taken to keep cation exchange capacity and initial pH close to the same on amended and unamended (control) soils. Urea was surface‐applied to amended and unamended soils and ammonia volatilization and soil surface pH were measured. The increase of H+ buffering capacity of soils was found to reduce soil surface pH and NH3 volatilization after application of urea. It is concluded from this work that H+ buffering capacity of a soil is a better indicator of NH3 loss potential than a soil's initial pH.