A system for the measurement in the field of losses of ammonia through volatilisation

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Abstract
A detailed description is given of the construction and operation of a system of small wind‐tunnels used in the measurement of ammonia volatilisation from grass swards. In the design of the system, emphasis was placed on the requirements that (i) natural sward conditions should be influenced as little as possible, and (ii) airspeed through the tunnels should be controllable in the range normally encountered in the field. An analyser is described which incorporates an ammonia‐sensing probe; it was used to monitor automatically and continuously the concentration of ammonia in air entering and leaving the tunnels. The tunnels were found to have only small effects on sward conditions. Differences between simultaneous measurements of temperature made inside and outside the tunnels were rarely more than 1°C for air temperature and 2°C for soil temperature at 3 cm depth. The potential of the system was examined in a study comparing the loss of ammonia through volatilisation from swards treated with natural urine or an artificial urine. There were marked differences in the rates of volatilisation from the two urines although the total loss of nitrogen was similar from both, amounting to about 3% of the nitrogen applied.