Soil Organic Carbon Significantly Increases When Perennial Biomass Plantations Are Reverted Back to Annual Arable Crops

Abstract

The cultivation of perennial biomass crops (PBCs) on marginal lands is necessary to provide feedstock for the bio-based EU economy and accrue environmental benefits through carbon (C) sequestration in soil. Short rotation coppice (SRC) species, e.g., willow, black locust, and poplar, and perennial rhizomatous grasses, e.g., miscanthus, switchgrass, and giant reed, have been tested in many EU projects in the last 10 years to investigate their productive potential and contribution to the mitigation of climate change. A major knowledge gap regarding PBCs is the fate of accumulated soil organic carbon (SOC), once PBC plantations are reverted to arable crops. In this study, the effects of PBCs reversion on SOC and carbon-dioxide emission (CO2) were monitored over a 2-year period in a long-term (11-year) multispecies trial of six PBCs: Three SRC species including poplar (Populus spp.), willow (Salix spp.), and black locust (Robinia pseudoacacia), and three herbaceous rhizomatous grasses including miscanthus (Miscanthus x giganteus), switchgrass (Panicum virgatum), and giant reed (Arundo donax). The SOC change and GHG emissions were then modeled with the ECOSSE model. Two years after the reversion, SOC increased significantly for all PBCs with no significant difference between them. During the PBC cultivation phase, 5.35 Mg SOC ha−1 was sequestered while 10.95 Mg SOC ha−1 was added by reversion, which indicated that 67% of SOC sequestration occurred after the reversion. The ECOSSE model was successfully used to simulate SOC sequestration trajectories (R2 = 0.77) and CO2 emission from soil (R2 = 0.82) after the reversion of the six PBCs. This indicated that the high SOC sequestration rate after the reversion was due to humification of belowground biomass (roots + rhizomes/stumps), which had been mulched and incorporated into the reversion layer (0–30 cm). This occurred in the first 2 months (on average 5.47 Mg SOC ha−1 y−1) and in the first year after the reversion (1.3–1.8 Mg SOC ha−1 y−1). Considering the entire PBCs cultivation cycle (13 years of PBCs + reversion), PBCs showed annual SOC sequestration rates higher than 1 Mg SOC ha−1 y−1, placing PBCs cultivation and reversion as one of the most promising agricultural practices to combine biomass production, with the recovery of marginal lands to agricultural production through increasing the SOC.

Early impacts of marginal land‐use transition toMiscanthuson soil quality and soil carbon storage across Europe

“…Plant C input to soil from above‐ and belowground biomass components were estimated as described in Martani et al. (2023) for perennial biomass crops with the addition of the formula to estimate C input from rhizomes (Table S3). Total C input to soil was calculated on a yearly basis as the sum of the C input from the following plant organs: C from stubble (Cs), C from roots (Cr), C from root exudates (Ce), and C from rhizomes (Crhiz).…”

“…(2022) for the same plot/hybrid/year/site combination, while information about harvest index was obtained from Martani et al. (2023) and root to shoot (R:S) ratio values from dedicated roots sampling at PAC1 and OLI sites.…”

“…A detailed description of RB estimation is reported in the Supporting Information. To apply the formula of Table S3 the data on annual yields were obtained from Awty-Carroll et al (2022) and Magenau et al (2022) for the same plot/hybrid/year/site combination, while information about harvest index was obtained from Martani et al (2023) and root to shoot (R:S) ratio values from dedicated roots sampling at PAC1 and OLI sites.…”

Perennial biomass cropping and use: Shaping the policy ecosystem in European countries

“…In addition, actual GHG flux measurements in paired sites representing land‐use change and original land use are only just starting to be undertaken, one example being the PBC4GGR project in the UK (https:// pbc4ggr.org.uk ), where verification and reporting of soil carbon change will be carried out by combining on‐site eddy covariance monitoring with modelling (Dondini et al, 2016 ; McCalmont, McNamara, et al, 2017 ). At the end of the crop lifespan the root and rhizome biomass of the PBCs is incorporated in the soil by maceration and is decomposed relatively quickly (Martani et al, 2023 ). It should be noted that reversion to previous land use will likely result in a return over time to soil carbon levels commensurate with that land use and therefore should not be used for carbon credits.…”

Integrating perennial biomass crops into crop rotations: How to remove miscanthus and switchgrass without glyphosate

“…Studies that look at the removal of miscanthus and switchgrass are limited, mostly focusing on a single genotype and employing the herbicide glyphosate as a removal method (Anderson et al, 1997(Anderson et al, , 2011Brown et al, 2014;Dufossé et al, 2014;Franco et al, 2018;Mangold et al, 2019;Martani et al, 2023;Rowe et al, 2020), whereby this tight focus limits how well the results of these studies can be applied more generally. The vast majority of studies on miscanthus have dealt with the standard commericial genotype Miscanthus × giganteus a naturally occuring hybrid of Miscanthus sinensis and Miscanthus sacchariflorus.…”