Estimating Ammonia Volatilization from Swine‐Effluent Droplets in Sprinkle Irrigation

Abstract

Irrigation of swine effluent is one of the most economical ways to dispose of swine manure. The determination of appropriate application rates requires the quantification of volatilization losses of ammoniacal N. In this research, a mechanistic model was developed to estimate droplet volatilization loss (excluding drift losses) of ammoniacal N from swine effluent in sprinkler irrigation. Field experiments were conducted to validate the model. The model combined energy balance, mass balances of ammoniacal N, and water to predict equilibrium temperature of a droplet, and losses of ammoniacal N and water from a droplet. Trajectory analysis was employed in the model to estimate a droplet's exposure time in air. Mass and heat transfer coefficients developed in boundary layer theory were incorporated in the mass and energy balance equations to predict fluxes of heat, ammoniacal N, and water. Equilibrium constants of transformation reactions were used in the model to establish relationships among component species of ammoniacal N. Field experiments measured concentrations of ammoniacal N in swine‐effluent samples collected at the nozzles and ground surface to determine the loss of ammoniacal N caused by droplet volatilization. The measured concentration decreases were combined with water loss percentages to estimate percentage losses of ammoniacal N. Results from both field experiment and mathematical modeling indicated that loss of ammoniacal N from droplet volatilization was only a few percentages which was considered insignificant compared with common soil surface volatilization loss of 20 to 50% at the end of 1 wk after application.