IN-SITU MEASUREMENT OF AMMONIA EMISSIONS FROM ORGANIC FERTILIZERS IN PLOT EXPERIMENTS

Ammonia volatilization from slurry in the field is either measured und er open atmosphere from large field plots (integrated horizontal flux [IHF], mass balance) or in closed, ventilated chambers (e.g., wind tun nels), which allow the measuring of small plots but influence the clim atic conditions. We conducted this study to evaluate a new method for measuring NH3 volatilization on small experimental plots under ambient climatic conditions (including rain and,wind). Various pretreated cat tle slurries were applied to small plots (2 by 2 m) in tillering winte r wheat (Triticum aestivum L.). Ammonia collected by passive samplers on manured plots was compared with NH3 collected on standard plots. wh ere known rates of NH3 were being released via a tubing system (standa rd comparison [SC] method). Forty-five manured plots were measured sim ultaneously by comparison with two standard plots. The specific detect ion limit of this experiment was 2.5 mu g NH3-N m(-2) s(-1) (90 g NH3- N ha(-1) h(-1)). Below this value, the coefficient of variation of mea sured NH3 release exceeded 30%. Slurry was applied to plastic gutters on two control plots. Measured NH3 Losses front these plots accounted for 78% of the absolute NH4-N losses determined by sampling and analyz ing slurry from the gutters. Measurement of the control plots was repe ated during the ripening of the wheat. A strong deviation between the measurements of the two plots suggested that the accuracy of the new m ethod is limited in dense vegetation. The results are discussed with r espect to measurement accuracy and possible sources of error. A compar ison with literature reports indicated that the accuracy of the SC met hod compared favorably to micrometeorological methods and wind-tunnel systems.