Modeling of Ammonia Emissions from Soils

Abstract

Using a dynamic flow-through chamber system in conjunction with a Thermo Environmental 17C Chemiluminescence ammonia (NH3) analyzer, emissions from slurry-amended, that is, effluent from the lagoon (∼33 kg N ha-1) and nonamended soils were calculated at a swine farm in eastern North Carolina. The average NH3-N flux values during the period when the soils were not amended with any slurry were ∼54 ng N m-2 s-1, while the average NH3-N flux values measured immediately following the application of slurry to the soil were 1723.9 ng N m-2 s-1. An empirical model relating soil temperature to NH3 flux for nonamended soils explained over 70% of the variability in NH3 emissions; however, a similar empirical model relating soil temperature to NH3 flux for slurry-amended soils was able to explain only 39% of the variability in NH3 emissions. A mass transport model, based on physical and chemical processes to estimate NH3 emissions from recently amended soils is also presented and compared and contrasted to the empirical model. The variables used in the mechanistic model are pH, soil temperature, and total ammoniacal nitrogen content. When using the mass transport model, the percentage difference between predicted and measured values for the nonamended and slurry-amended soils were 164 and 16%, respectively, indicating that the mechanistic model is only applicable for periods when nitrification/denitrification, plant uptake, and immobilization are small enough in comparison to the chemical and physical processes following slurry application that they can be ignored. The percentage of the nitrogen (N) applied, which was emitted as NH3, increased at its greatest rate immediately following slurry application (1–2 days) and then began to level out at a value of approximately 20% by day 4. Previous laboratory studies found these volatilization events to be short lived (few days–2 weeks), and this study corroborates those findings.