Integrated evaluation of greenhouse gas emissions (CO₂, CH₄, N₂O) from two farming systems in southern Germany

Agricultural practices contribute to emissions of the greenhouse gases CO₂, CH₄ and N₂O. The aim of this study was to determine and discuss the aggregate greenhouse gas emission (CO₂, CH₄ and N₂O) from two different farming systems in southern Germany. Farm A consisted of 30.4 ha fields (mean fertilization rate 188 kg N per ha), 1.8 ha meadows, 12.4 ha set-aside land and 28.6 adult beef steers (year-round indoor stock keeping). Farm B followed the principles of organic farming (neither synthetic fertilizers nor pesticides were used) and it consisted of 31.3 ha fields, 7 ha meadows, 18.2 ha pasture, 5.5 ha set-aside land and a herd of 35.6 adult cattle (grazing period 6 months). The integrated assessment of greenhouse gas emissions included those from fields, pasture, cattle, cattle waste management, fertilizer production and consumption of fossil fuels. Soil N₂O emissions were estimated from 25 year-round measurements on differently managed fields. Expressed per hectare farm area, the aggregate emission of greenhouse gases was 4.2 and 3.0Mg CO₂ equivalents for farms A and B, respectively. Nitrous oxide emissions (mainly from soils) contributed the major part (about 60%) of total greenhouse gas emissions in both farming systems. Methane emissions (mainly from cattle and cattle waste management) were approximately 25% and CO₂ emissions were lowest (circa 15%). Mean emissions related to crop production (emissions from fields, fertilizer production, and the consumption of fossil fuels for field management and drying of crops) was 4.4 and 3.2 Mg CO₂ equivalents per hectare field area for farms A and B, respectively. On average, 2.53% of total N input by synthetic N fertilizers, organic fertilizers and crop residues were emitted as N₂O-N. Total annual emissions per cattle unit (live weight of 500 kg) from enteric fermentation and storage of cattle waste were about 25% higher for farm A (1.6 Mg CO₂ equivalents) than farm B (1.3 Mg CO₂ equivalents). Taken together, these results indicated that conversion from conventional to organic farming led to reduced emissions per hectare, but yield-related emissions were not reduced.