Greenhouse gas balances and yield-scaled emissions for storage and field application of organic fertilizers derived from cattle manure

Summary

Manure treatment such as anaerobic digestion and solid-liquid separation has shown a potential to abate
greenhouse gas (GHG) emissions, but few studies have considered GHG emissions from both storage and field
application regarding crop yield. In this study, four different organic fertilizers were studied: untreated cattle
manure (CA); digestate of cattle manure anaerobically co-digested with grass-clover (DD); a liquid fraction from
the separation of DD (LF); and a liquid fraction derived from a biogas desulfurization biofilter enriched with
sulfur and ammonium (NS). The CH4, N2O and NH3 emissions during storage of CA, DD and LF between August
and November 2020 (11 weeks) were quantified. Storage continued until April 2021 when these materials, as
well as the NS fertilizer and a mineral NKS fertilizer, were applied at a rate of 100 kg total N/ ha to spring
barley. N2O emissions and soil mineral N content were monitored during the growing season. Overall, CH4
emissions during storage were the main source of GHG emissions independent of treatments, accounting for 85
%, 40 % and 11 % of total GHG emissions (based on field application of 100 kg/ ha total N) from treatments CA,
DD and LF, respectively. Anaerobic digestion and separation significantly reduced CH4 emissions during storage
due to the diminished content of degradable organic matter available for methanogens. The N2O emissions from
treatments CA, DD, and LF during storage were not significantly different. Treatments DD and LF emitted more
NH3 than CA during storage, presumably because of higher pH and ammonium content. In the field experiment,
the dilute solution of NS emitted the most N2O, while emissions from treatments CA, DD and LF were comparable.
Yield-scaled GHG emissions for treatments CA, DD, LF and NS during both periods of storage and field
were 44.4, 17.1, 8.5 and 24.3 kg CO2 eq/ hkg grain yield, respectively. Anaerobic digestion with or without
separation were thus effective strategies for the mitigation of GHG emissions from cattle manure in this study.
Yields and nitrogen use efficiencies of the processed manure materials were not significantly different from those
observed with the same N application rate as inorganic fertilizer, and hence anaerobic digestion with or without
separation were promising GHG mitigation strategies