Experiments conducted between August 1999 and April 2002 evaluated anhydrous ammonia manifold distribution during field application at 84- and 168-kg N/ha (75- and 150-lb N/acre) application rates. Multiple manifolds including the conventional (Continental NH3 Model 3497, Dallas, Tex.), Vertical-Dam (Continental NH3 Dallas, Tex.), RotaflowTM(H.I. Fraser Pty Ltd, Sydney, Australia), Equa-flowTM(PGI International, Houston, Tex.), FD-1200 prototype (CDS John Blue Co., Huntsville, Ala.), and the Impellicone prototype manifold were tested. Temperature and pressure data were collected along the flow path.

Results showed high distribution variation by the conventional manifold at both application rates, with average coefficient of variation (CV) values in excess of 16%. At the 84-kg N/ha (75-lb N/acre) rate, all other manifolds tested had significantly lower application variation (. = 0.05). At the 168-kg N/ha (150-lb N/acre) rate, the conventional manifold grouped statistically with the Vertical-Dam with a corn ring and the FD-1200 prototype, producing CV values between 9.5% and 16.2%. All other manifolds had significantly lower application variation. The Impellicone, Rotaflow., and Equa-flow., manifolds performed with the lowest measured variation at both rates, yielding best performance at the 168-kg N/ha (150-lb N/acre) rate with CV in the 6% range.

Analysis of recorded temperature and pressure data indicate that NH3 flowing through the system very closely follows the saturation line and acts as a saturated mixture. Predictions of NH3 quality based on calculations of an ideal adiabatic mixture are supported by this result. Investigation for correlation between CV, air temperature, and percent of volume in the vapor phase of NH3 resulted in only a visual trend that may suggest a reduction in CV with lower percent of volume in the vapor phase.

Results suggest that replacement of a conventional manifold with a Vertical-Dam manifold or any of the other manifolds tested could reduce application variation between 7.0% and 16.5% at 84 kg N/ha (75 lb N/acre) and 1.0% and 10.2% at 168 kg N/ha (150 lb N/acre). This change could reduce application rate by eliminating the need for over-application to compensate for variations.