Nitrous oxide, methane and ammonia emissions following slurry spreading on grassland

Abstract

Abstract In Sweden, 90% of ammonia (NH 3 ) emissions to the atmosphere originate from agriculture, predominantly from animal manure handling. It is well known that incorporation of manure into soil can reduce NH 3 emissions after spreading. However, there is a risk of increased nitrous oxide (N 2 O) and methane (CH 4 ) emissions caused by bacterial activity and limited oxygen availability under these conditions. A full‐scale injector was developed and evaluated in a field experiment on grassland. Cattle slurry was either injected in closed slots 5 cm below ground or band spread on the soil surface above the crop canopy at a rate of 25 t ha −1 . In a control treatment, no slurry was applied. During a 5‐day period after application, NH 3 emissions were measured using an equilibrium concentration method. Gas samples for estimating CH 4 and N 2 O emissions were also collected during 7 weeks following slurry application. Injection in closed slots resulted in no detectable NH 3 emissions. After band spreading, however, NH 3 emissions corresponded to nearly 40% of the total ammoniacal nitrogen in the applied slurry. The injection of slurry gave rise to a broad peak of N 2 O emissions during the first 3 weeks after application. In total, for the measuring period, N 2 O emissions corresponded to 0.75 kg N ha −1 . Band spreading resulted in only a very small N 2 O release of about 0.2 kg N ha −1 during the same period. Except for the first sampling occasion, the soil was predominantly a sink for CH 4 in all the treatments. The use of the injector without slurry application reduced grass yield during unfavourable growing conditions. In conclusion, shallow injection in closed slots seems to be a promising technique to reduce negative environmental impacts from NH 3 emissions with a limited release of N 2 O and CH 4 .