Reducing Ammonia Emissions from Digested Animal Manure: Effectiveness of Acidification, Open Disc Injection, and Fertigation in Mediterranean Cereal Systems

Ammonia poses a risk to human health and terrestrial and aquatic ecosystems. In Spain in 2022, the agricultural sector was responsible for 97% of ammonia emissions to the atmosphere, with the application of animal manure as fertilizer accounting for 24.4% of these emissions. The search for effective mitigation strategies in the application of animal manures is imperative to support the implementation of policies that contribute to the sustainability of the agricultural sector. The aim of this study is to evaluate three digestate application techniques, namely, acidification, open disc injection, and fertigation, in a wheat–maize rotation and compare them to traditional trail hose application. In spring wheat topdressing, acidification is the most efficient method for reducing ammonia emissions, followed by disc injection and, finally, fertigation. In the summer base dressing to maize, acidification is the best method, with more than 70% reduction compared with trail hoses. In terms of both base dressing and side-dressing fertilization, the most efficient method is fertigation, with a 70% reduction, followed by acidification and disc injection (>25%). Although the three methods reduce ammonia emissions, they have certain drawbacks: fertigation requires previous solid/liquid separation, acidification requires ad hoc equipment, and disc injection requires high mechanical traction.