Closing cycles on the farm and in the region

Today, many farms in arable regions of eastern Austria and elsewhere operate without livestock and depend on external fertilizers whose prices are subject to increasing inflation. Clover grass is essential for organic farms to supply nitrogen to the crop rotation. Cutting and taking away clover grass biomass increases the amount of nitrogen fixed, but the biomass has no use as fodder on stockless farms.

In the EIP-AGRI project Closing Cycles, innovative measures for utilizing residual materials on the farm and in the region were tested in practical trials. Two different forms of cut-and-carry were investigated, one using clover grass as transfer mulch, the other incorporating hay into the soil of arable fields; cooperations between farms exchanging clover grass for manure or slurry; and a cooperation in which clover grass was delivered to a biogas plant in exchange for digestate. Also, three different composting methods were tested.

Nitrogen and carbon balances were calculated for all measures. All substrates used in the various processes, such as clover grass, hay, straw and wood chips, were sampled and analyzed before being composted, fed, exchanged, or transferred on farms. The resulting organic fertilizers such as compost, manure, or slurry were also analyzed. Carbon footprints were calculated and an economic assessment was conducted while the participating farmers provided evaluation concerning practicality.

The closed-loop management measures enable a targeted use of the nitrogen produced by the clover grass for crops that require a copious nitrogen supply. Due to the lack of information published on the carbon footprints of commercial organic fertilizers suitable for organic farming, the measures were compared against mineral nitrogen fertilizer as a benchmark. These calculations showed that, compared to the use of synthetically produced nitrogen fertilizer, net savings of 200-600 kg of greenhouse gases (CO₂e) per 100 kg of nitrogen applied were achieved with all measures. Carbon footprint results, however, vary strongly depending on the type of machinery used.

As transport distances of residual materials and received organic fertilizers increase, the share of emissions caused by transport rises steeply. At a distance of 0.5 km, transport CO₂e emissions accounted for an average of 3.4% of total emissions. At a distance of 4 km, transport emissions rose to 22% of total emissions, and at 10 km, transport accounted for 41%.

Compared with other commercial fertilizers suitable for organic farming priced at 7 € per kg of nitrogen, all tested measures of closed-loop management, except for the examples of clover grass/slurry cooperation and clover grass composting with charcoal, achieved net cost savings of about 130-400 € per 100 kg N. These figures do not take into account the price increase in 2022. Additional benefits of closed-loop measures such as erosion control, protection from evaporation, micronutrient fertilization and increase of soil organic matter were not included in the calculation.

The results show that closing cycles on the farm and in the region is favorable regarding the carbon footprint as well as financially, if it is ensured that transport distances are kept short and that machinery input is kept as low as possible.