Measurement of emission and deposition patterns of ammonia from urine in grass swards

Currently, legislation is being considered to reduce NH3 emissions in the U K. The major sources of NH3 and their relative contributions are well known , however, the processes that control the rates of emission ale still poorl y defined. A series of wind-tunnel experiments has been carried out to dete rmine the effects of various management practice on NH3 losses. The tunnels were modified to enable NH3 emission and subsequent deposition to the adja cent swards in the field to be measured. The wind-tunnels were used to exam ine the effects of herbage length, cutting and N status on rates of NH3 flu xes, which together with the prevailing environmental conditions affected t he rates of NH3 emission and deposition. Results showed that between 20 and 60% of the NH3 emitted was deposited within 2 m. Compensation points of be tween 1.0 and 2.3 mug m(-3) were calculated for the grass sward. (C) 2001 E lsevier Science Ltd. All rights reserved.