The effects of temperature and rate of application on NH3-N volatilization from NH4+ salts applied to the surface of a calcareous soil were investigated in the laboratory. Total NH3-N losses were only slightly influenced by temperature over a broad range of NH4+-N application rates with a precipitate forming NH4+ compound such as (NH4)2SO4 in a calcareous soil. The rates of NH3-N loss were highly influenced by temperature. High temperatures increased the initial rates of NH3-N loss although they were proportionally reduced at later stages. The lowest temperature resulted in the lowest initial NH3-N loss rate but became highest for the last 76 hours. Total ammonia nitrogen losses were dependent on the rate of NH4+-N application. The quantity of NH3-N loss varied from 19 to 50% of the applied NH4+-N at 33 to 550 kg NH4+-N/ha, respectively.
The increasing temperature increased losses of NH3-N from NH4NO3 which does not form precipitates with CaCO3 or appreciable (NH4)2CO3. In 100 hours, NH4NO3 lost 14, 18, and 26% of the applied NH4+-N at 12, 22, and 32C, respectively. Both the total 100-hour NH3-N losses and rates of NH3-N loss were increased by increased temperatures; however, the percent of NH3-N volatilized was unaffected by rates of NH4+-N application.
Ammonium sulfate losses from a noncalcareous Wilson clay loam buffered to the pH of the calcareous soil produced NH3-N losses equivalent to NH4NO3 at 12C and lower than NH4NO3 at 32C. Ammonia nitrogen losses, both total NH3-N and rates of NH3-N loss, were similar to losses of NH4NO3 from the calcareous soils. Therefore in the calcareous Houston Black clay the NH3-N loss caused by reaction of (NH4)2SO4 with CaCO3 ranged from 0 to 70 or 80%.
Regression equations were developed that predict NH3-N losses at certain temperatures, time, and rate of NH4+-N application.