Odour emission arising from application of livestock slurries on land: Measurements following spreading using a micrometeorological technique and olfactometry

Abstract

Livestock slurries were applied to grass or arable land, following which a simplified, micrometeorological technique was used in the collection of odorous air samples. On arable land, pig slurry was either left on the soil surface as a control or incorporated by means of a plough, rotary harrow or rigid tines. Odour concentration (odour units per m3 air) was subsequently determined by dynamic dilution olfactometry and rates of odour emission (odour units per second) calculated. From grassland, odour concentrations were greater for pig than for cattle slurry, especially when the former had been withdrawn from the settled layers near the bottom of a storage pit. The pattern of odour emission decayed exponentially with time; high rates of emission during the first few hours were followed by much lower rates between 6 and 60 h after application with small diurnal fluctuations. On arable land, ploughing immediately after application reduced the rate of odour emission during the first hour by 85% and rotary narrowing reduced it by 45% whereas the result when rigid tines were used was similar to the control. A worthwhile reduction (52%) in total emission (odour units) over 48 h was achieved only by immediate ploughing. No reduction in total emission was detected when incorporation, by any means, was delayed for 3 to 6 hr after slurry application.