Techniques for Measuring Ammonia Emissions from Land Applications of Manure and Fertiliser

Land application of manures represents a major source of ammonia (NH₃) emissions to the atmosphere in Europe, often accounting for 30-40% of the total national emission. A number of techniques have been developed to quantify NH₃ emissions for the construction of national inventories, so that the impacts on the environment can be assessed and the effectiveness of abatement strategies evaluated. These techniques are equally applicable to the measurement of emissions from fertiliser applications. Generally, the techniques fall into one of two categories: micrometeorological methods (usually used for large land areas) and enclosure methods (commonly used on small plots). Most techniques require the measurement of NH₃ concentration and air flow or wind speed, or, alternatively, direct measurement of NH₃ flux. This paper will briefly present a range of available techniques and then concentrate on the three techniques most often used in Europe.

The integrated horizontal flux (IHF) mass balance technique is the most widely used micrometeorological measurement technique, employing either acid–filled absorption flasks (‘bubblers’) for measurement of NH₃ concentration or, more commonly now, passive flux samplers (‘shuttles’) for direct NH₃ flux measurement. Wind tunnels are the most commonly used small-plot technique, with acid-filled absorption flasks employed to measure NH₃ concentration. The equilibrium concentration technique lies somewhere between a classical micrometeorological technique and an enclosure technique and uses passive diffusion samplers (PDS) for the measurement of NH₃ concentration. A series of experiments was conducted to assess the variability and accuracy of the samplers used in each technique and the variability of the techniques as a whole in measuring emissions from different manure types. For the samplers, coefficients of variation (CVs) were 21, 10 and 14% and limits of detection were 70, 50 and 2.5 ug N for ’bubblers’, ‘shuttles’ and PDS, respectively. For the emission measurement techniques as a whole, CVs following spreading of different manure types were in the ranges of 23-57, 31-76 and 22-39% for the IHF, wind tunnels and equilibrium concentration techniques, respectively. Lower CVs were associated with measurements following slurry application compared with solid manure application. The equilibrium concentration technique was considered to be the least robust of the methods as the PDS were susceptible to under- or over-exposure. The development of a reliable, non-intrusive technique for measuring emissions from small plots is still required.

⁽¹⁾Institute of Grassland and Environmental Research, North Wyke, Okehampton, DevonEX20 2SB, UK 2ADAS Gleadthorpe, Meden Vale, Mansfield, Nottinghamshire NG20 9PF, UK
*Corresponding author