Measured and modelled effect of land‐use change from temperate grassland to Miscanthus on soil carbon stocks after 12 years

Abstract

Soil organic carbon (SOC) is an important carbon pool susceptible to land‐use change (LUC). There are concerns that converting grasslands into the C4 bioenergy crop Miscanthus (to meet demands for renewable energy) could negatively impact SOC, resulting in reductions of greenhouse gas mitigation benefits gained from using Miscanthus as a fuel. This work addresses these concerns by sampling soils (0–30 cm) from a site 12 years (T12) after conversion from marginal agricultural grassland into Miscanthus x giganteus and four other novel Miscanthus hybrids. Soil samples were analysed for changes in below‐ground biomass, SOC and Miscanthus contribution to SOC (using a 13C natural abundance approach). Findings are compared to ECOSSE soil carbon model results (run for a LUC from grassland to Miscanthus scenario and continued grassland counterfactual), and wider implications are considered in the context of life cycle assessments based on the heating value of the dry matter (DM) feedstock. The mean T12 SOC stock at the site was 8 (±1 standard error) Mg C/ha lower than baseline time zero stocks (T0), with assessment of the five individual hybrids showing that while all had lower SOC stock than at T0 the difference was only significant for a single hybrid. Over the longer term, new Miscanthus C4 carbon replaces pre‐existing C3 carbon, though not at a high enough rate to completely offset losses by the end of year 12. At the end of simulated crop lifetime (15 years), the difference in SOC stocks between the two scenarios was 4 Mg C/ha (5 g CO2‐eq/MJ). Including modelled LUC‐induced SOC loss, along with carbon costs relating to soil nitrous oxide emissions, doubled the greenhouse gas intensity of Miscanthus to give a total global warming potential of 10 g CO2‐eq/MJ (180 kg CO2‐eq/Mg DM).

Projections of global and UK bioenergy potential from Miscanthus × giganteus—Feedstock yield, carbon cycling and electricity generation in the 21st century

“…), Milner et al () suggest that if the UK land without constraints were planted with miscanthus, 99.6% would see net gains in SOC between 1.5 and 2.5 Mg C ha −1 year −1 . Given that the only substantial negative SOC changes in Figure are located on uplands of high C soils, our simulation for 2010–2019 agrees with this finding, although we caution that the potential for soil C storage under miscanthus largely depends on the land use system it is replacing (Dondini et al, ; Holden et al, ).…”

“…We caution that our simulations are for a mature miscanthus crop, and do not include emissions resulting from past land use conversion. Holder et al () modelled miscanthus, underpinned by experimental soil C change, and concluded that C change is dependent on former land use. Converting grassland to miscanthus can increase global warming potential during the first 15 years.…”

Miscanthus: A fast‐growing crop for environmental remediation and biofuel production

“…The net release of three primary greenhouse gases (N 2 O, CH 4 , and CO 2 ) is estimated to reduce to an extent of 4.08 t CO 2 ‐eq per hectare per year (Mi et al., 2018). If we divert to grow Miscanthus on the grassland, soil carbon sequestration would be of significant difference in the long run (Holder et al., 2019). In one life cycle (15 years), it is estimated that Miscanthus will release twice amount of greenhouse gas compared to the current habituated grasses.…”

Enhanced Carbon Sequestration in Marginal Land Upon Shift towards Perennial C4Miscanthus × giganteus: A Case Study in North-Western Czechia

“…In most European countries, fossil fuels (coal and gas) are still the main source of energy production and represent a major source of greenhouse gases and air pollution [1,2]. To combat the resulting negative environmental and health impacts, EU members modi-fied their targets for 2030 to achieve at least 40% reduction of greenhouse gases (GHGs) emissions and reach a share of at least 32% in renewable energy compared with 1990 [3].…”

“…These lignocellulosic rich feedstocks are mainly perennial grasses such as Miscanthus x giganteus or switchgrass [12,13]. Having in mind the limited area of agricultural land and to avoid the food production conflict, cultivation of such high biomass crops is becoming more favorable on marginal and less fertile lands unsuitable for arable crops [1,11,14]. Hence, the increase in their volume over the past 15 years is justifiable [15].…”