The aim of this study was to investigate the effect of different application techniques on greenhouse gas emission from co-fermented slurry. Ammonia (NH3), nitrous oxide (N2O), and methane (CH4) emissions were measured in two field experiments with four different application techniques on arable and grassland sites. To gather information about fermentation effects, unfermented slurry was also tested, but with trail hose application only. Co-fermented slurry was applied in April at a rate of 30 m3 ha(-1). Measurements were made every 4 h on the first day after application and were continued for 6 wk with gradually decreasing sampling frequency. Methane emissions were <150 g C ha(-1) from co-fermentation products and seemed to result from dissolved CH4. Only in the grassland experiment were emissions from unfermented slurry significantly higher, with wetter weather conditions probably promoting CH4 production. Nitrous oxide emission was significantly increased by injection on arable and grassland sites two- and threefold, respectively. Ammonia emissions were smallest after injection or trail shoe application and are discussed in the preceding paper. We evaluated the climatic relevance of the measured gas emissions from the different application techniques based on the comparison of CO2 equivalents. It was evident that NH3 emission reduction, which can be achieved by injection, is at least compensated by increased N2O emissions. Our results indicate that on arable land, trail hose application with immediate shallow incorporation, and on grassland, trail shoe application, bear the smallest risks of high greenhouse gas emissions when fertilizing with co-fermented slurry.

Ammonia emissions after spreading animal manure contribute a major share to N losses from agriculture. There is an increasing interest in anaerobic co-digestion of liquid manure with organic additives. This fermentation results in a change of physical and chemical parameters of the slurry. Among these are an increased pH and ammonium content, implying a higher risk of NH3 losses from fermentation products. To compare different application techniques and the effect of fermentation on NH3 volatilization, we used the standard comparison method and tested it for reliability. This method seems to be perfectly suited for experiments with a large number of treatments and replicates if prerequisites concerning the experimental layout are considered. We tested four different application techniques on arable and grassland sites. The more the substrate was incorporated into the soil or applied near the soil surface on the grassland site, the less NH3 was lost. Injection of the substrate reduced losses to less than 10% of applied NH4+ on both sites, whereas losses after splash plate application amounted to more than 30%. Trail shoe application on grassland performed as well as injection. Harrowing on arable land also reduced emissions efficiently, if harrowing occurred within the first 2 h after application. Emissions from trail hose-applied co-fermentation product were not greater than from unfermented slurry. Better infiltration of the less viscous substrate seemed to have compensated for the increased loss potential.