AMMONIA VOLATILIZATION FOLLOWING SURFACE-APPLIED PIG AND CATTLE SLURRY IN FRANCE

Field experiments were carried out in Brittany (Western France) in 1993 to measure ammonia losses from surface-applied pig and cattle slurry. Experiments were conducted on grass, stubble (wheat and maize) and arable land using a wind tunnel system. Ammonia losses were followed during periods ranging from 20 to 96 h after slurry application. Rates of slurry applied varied from 40 to 200 m(3)/ha. In two experiments, losses from cattle slurry were respectively 75 and 54% of the ammoniacal nitrogen applied in the slurry. Ammonia emissions from pig slurry applied at a rate of 40 m(3)/ha, during spring and summer experiments, were higher on grass (45-63% of the total ammoniacal nitrogen applied) than on wheat stubble (37-45%). On average, 75% of the total loss in all experiments occurred within the first 15h after spreading. Significant correlations were found between ammonia losses (kg N/ha) and mean soil temperature and slurry dry matter content (%) using simple linear regressions and stepwise procedures. The time of application was also found to influence the magnitude of ammonia loss: 83% of the total loss occurred within 6 h when the slurry was applied at midday compared with 42% when it was applied in the evening.