Ammonia emission measurement with an online wind tunnel system for evaluation of manure application techniques

Field application of liquid manure contributes substantially to atmospheric ammonia. Low emission application methods are commonly used to reduce ammonia transfer to the atmosphere. To document which application method results in lower ammonia volatilization there is a need for high precision measurements to ensure that small differences in total emission and emission patterns can be quantified. This paper presents the evaluation and application of a new system of dynamic chambers (wind tunnels) with online cavity ring down spectroscopy measurements of ammonia. The system allows for high time resolution of 104 min throughout the measuring period (>= 90 h) when testing two treatments and one reference in triplicates. Measurement variability is low with a coefficient of variation of 13 +/- 8% within triplicates. The system was used to investigate the effect of trailing shoes compared to trailing hoses on different soil and crop types, where the expected differences in ammonia volatilization are low. The results show that when applying pig slurry on coarse sand a significant reduction of 47 +/- 20% was obtained, whereas the reduction when applied on loamy sand and sandy loam was lower and occasionally insignificant. During ten experiments on three different soil types, an overall average reduction of ammonia volatilization from using trailing shoes compared to trailing hoses was found to be 19 +/- 12%. Furthermore, the importance of correct use of trailing hoses was examined by comparing with application above the crop canopy. Application at the ground surface gave an ammonia emission reduction of 40 +/- 13% compared to application 20 cm above the canopy.