Abstract

Due to increasing specialization, intensification and reduced use of bio-fertilizer, we have in Sweden today regions where we lose organic matter in arable land. Two regions in Skåne and Västra Götaland, characterized by cereal-dominated crop rotations and low animal density, were selected for the evaluation. The calculations showed that we currently lose carbon from arable land in the Västra Götaland region to an extent that contributes almost four times the equivalent of the greenhouse gas contribution from diesel use in farming. To reverse this trend, an increased supply of carbon is required, which can be obtained for example through higher supply of crop residues or by applying bio-fertilizer. In the alternate future scenarios analyzed, the crop rotations were changed to include grass in 2 of 6 years. In these regions, there is little demand for grass for animal feed, and the grass was instead used as an energy crop for biogas production. This choice was also made to illustrate the conflict as energy crops replace food / feed crops on arable land, and the advantages and disadvantages it may entail. The biogas produced was adopted use as fuel replacing diesel, and the produced bio-fertilizer was used in cultivation where it replaced mineral fertilizer. The soil carbon development in these alternative scenarios could be reversed, in Skåne to make farmland a carbon sink, in Västra Götaland so that today's soil carbon content could be maintained. To introduce grass in cereal crop rotation in these regions, 274,000 hectares, could contribute with 6.8 PJ per year of biogas, which is more than the entire current production in the country's biogas plants (5.6 PJ in 2014). The climate benefit in cultivation would be equivalent to 0.2 million t CO2-equivalents per year, and the use of biogas as a replacement for diesel would a similar emission reduction in addition. While the sustainability of arable land use was improved from a soil quality perspective, the grain production fell by 270 000 t (of which 2/3 spring barley) per year, equivalent to just over 10 % of today's cereal use for animal feed, and by more than 100 000 t of rapeseed, which is equivalent to 10 % of today's Swedish rapeseed-based biodiesel use. The life cycle assessment (LCA) also revealed other environmental impacts, such as that particle emissions would increase in production, but decrease as biogas replaced diesel and provide an overall decrease. The introduction of grass in the crop rotations reduced nitrogen leaching, but the biofertilizer utilization increased emissions of ammonia to air, resulting in an increased contribution to both eutrophication and acidification. The investigated change is thus not unambiguously positive, which shows the importance of a broad perspective in the evaluation of environmental impacts. The total socioeconomic value of the change amounted to 160 – 260 € per ha (per ha throughout the studied crop rotation), despite the negative contribution to eutrophication and acidification. In the surveyed regions, a support for environmental measures of 50 € per ha can be obtained for forage cultivation, where the aim is to stimulate sustainable crop cultivation and reduce leaching of nutrients. Forage is, despite this, only cultivated on a small portion of the arable land. We investigated which grass price that would be required for sustained revenue compared to the current crop rotation. This price was used to calculate the cost of the biogas produced in a newly built facility with grass as the only raw material. At current gas prices, grass would under these conditions be too expensive as biogas feedstock, a reduction in feedstock price of 20%, or an increase in gas price by 6% would be required to obtain a profitable production from biogas perspective. One condition would be that the production chain meets the demand on 60% reduction of greenhouse gas emissions that apply to new installations from 2015. This a prerequisite for biogas to be exempt from the CO2 tax in Sweden until 2020, and without this advantage, the biogas cannot compete with fossil fuel alternatives. Greenhouse gas reduction should be calculated according to the methodology in the EU renewable energy directive (EU RED). In this method, however, certain aspects, such as the soil carbon impacts of including grass in the crop rotation, are excluded. The climate benefits when using the EU RED methodology are thus much lower than at the LCA-based calculation, and grass for biogas could just barely meet the requirement of 60% reduction. As a comparison, calculations was also made for a region in Småland with high cattle density and grass cultivation on more than 80% of the arable land. Here, the evaluated modification was based on intensification of current grass production, and that the excess grass would be added to an existing biogas plant with cattle manure as the main feedstock. This option was under assumed conditions both economically viable and able to meet the EU RED requirements for greenhouse gas reduction. In this region, the soil carbon impact was small, and loss of soil carbon is not an issue at current arable land use. This illustrates how the value of the soil carbon impact is neither valued at an economic assessment or when the climate benefits are calculated according to the EU RED. It is therefore not an aspect of importance in the sustainability assessment based on these criteria alone. The EU RED takes the indirect impacts of land use (iLUC) into account, and that it can derail the entire climate benefit when certain food crops are used for biofuel production, but the big impact on the climate connected to soil carbon losses are excluded. The overall aim of this study was to produce data to improve understanding of the broad perspective needed for decisions on sustainable use of arable land. The loss of soil carbon is not sustainable in the long term, and measures must sooner or later be taken to reverse this trend. A sustainable use of arable land should give the lowest possible contribution to greenhouse gas emissions while food production is safeguarded in the long term. To introduce grass cultivation in cereal crop rotations according to the modified scenarios that have been studied here would halt or even reverse the present carbon loss from arable land. This would contribute to reduced greenhouse gas emissions, both in crop cultivation and in the transport sector. It may be socioeconomically justified to encourage this change, even if it meant a negative impact on some environmental aspects. It is important to broaden the perspective and to make sufficiently wide-ranging analyzes of such complex systems as the use of arable land. To take local conditions into consideration, to look at the effects of cultivation system and crop rotation instead of on individual crops and at the conflict between environmental objectives are the perspectives that were studied here. Sustainability criteria in the present EU renewable energy directive are not formulated taking local conditions and landscape perspectives into consideration. At present, the work on the EU bioenergy policy post 2020 is ongoing. To avoid contra productive measures, it seems important that future policies are formulated on a more broad level, and that sustainability criteria, where it is important to take local conditions and spatial perspectives into account, will be based on scientifically sound assessments at the national level.

Keywords

soil organic carbon greenhouse gas grass crops crop rotation GIS analysis SOC modelling

Published in

Energiforsk rapport
2016, number: 2016:280
ISBN: 978-91-7673-280-9
Publisher: Energiforsk

UKÄ Subject classification

Environmental Sciences related to Agriculture and Land-use
Renewable Bioenergy Research
Agricultural Science


Permanent link to this page (URI)

https://res.slu.se/id/publ/76622