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The crop rotation has a direct influence on GHG emissions of the farm. Each crop requires specific soil management (e.g. tillage), fertilizer applications, plant protection measures, irrigation practices, and harvest techniques (e.g. drying). All of these require different amounts of fossil fuels to be performed and thus have the direct implications for GHG emissions.
Nowadays, conventional farming systems work with narrow crop rotations or even without any rotation. Conventional crop rotations commonly consist of 2-3 crops of which usually 2 are cereals. In particular conventional cattle farms are characterized by a high percentage of maize cropping, used as livestock feed. These cereals are cultivated with high inputs of synthetic nitrogen fertiliser, requiring a high-energy use to be produced. Further, as most of the cropped cereals, such as maize, are additionally associated with the problem of soil organic matter losses, a new approach is needed which reduced GHG emissions and other associated problems of the common crop rotation systems.
In organic livestock farms, grass-legume (alfalfa, red and white clover, etc.) leys are a relatively common element, as the grass-legume mix can be used as fodder and the positive effects on soil fertility, pest management and nitrogen fixation in the soil are well known. However, for stockless farms even under organic management, the grass-legume biomass would have to be mulched, which involves a loss of financial value, nutrients and evokes nitrous oxide release.
The use of leguminous crops in the crop rotation cycle can help to stabilize or enhance soil fertility, sequester carbon (C), fixing N and therefore reducing GHG emissions. Also, the introduction of cover crops into the crop rotation as green manure increases soil organic carbon (SOC) stocks without a decline in yields.
What are the SOLMACC farmers doing?
In order to reduce GHG emissions on the farms, SOLMACC farmers implement different changes in their crop rotation systems, depending on their farm structures, size and technical/financial possibilities. For example, they:
- Introduced/extended grain legumes: farmers integrated grain legumes, such as soya, beans, winter peas and lupines into their crop rotation systems. These legumes substitute cereals and help to fix nitrogen and additionally sequester carbon.
- Introduced/extended forage legumes: farmers increased the share of forage legumes in the crop rotation. This was done by enriching the proportion of N fixing plant species in the current green manure mixture.
Stockless farms also implemented optimized crop rotations with grass-legume leys and the harvested biomass was used by agreed cooperating livestock or biogas producing farms, respectively. The farm residues of the livestock/biogas farm, be it farmyard manure or biogas digest, are brought back to the cropland of the stockless farm in amounts equivalent to the amount of nitrogen removed with the grass-clover biomass.
Two different cooperation models were established:
- Cooperation between stockless and livestock farms (stockless farm exports grass-legume, imports manure) are established.
- Cooperation with biogas producing farms: Biogas plants are often associated with intensive maize monocultures with all related negative environmental effects (soil erosion, fertiliser application, biodiversity decline); the use of grass-legume in biogas plants can help to increase the sustainability of biogas plants (increased carbon stock in soil under grass-legume mixtures, higher biodiversity, soil structure improvement and increased resilience to extreme weather events, biological nitrogen fixation).
These cooperations between livestock and stockless farms demonstrate a win-win situation for both farms, environmentally but also economically. As the grass-clover biomass will not be left anymore as much on the field but be removed instead, the associated nitrous oxide emissions will decrease along with an overall increase of the N-fixation performance of the grass-legume system. The livestock and/or biogas farm receives additional feed stuff and can, therefore, increase its intensity without further land use expansion. The cooperation is also economically viable since biogas can be produced by using the grass-legume and thereby using fixed nitrogen and increase the overall efficiency of the system.