Low risk management intervention: Limited impact of remedial tillage on net ecosystem carbon balance at a commercial Miscanthus plantation

• Published in: Global change biology. Bioenergy Vol. 16; no. 1
• Main Authors: Rowe, R. L., Cooper, H. M., Hastings, A., Mabey, A., Keith, A. M., McNamara, N. P., Morrison, R.
• Format: Journal Article
• Language: English
• Published: Oxford John Wiley & Sons, Inc 01-01-2024; John Wiley and Sons Inc; Wiley
• Subjects: Agricultural production; Carbon dioxide; Climate change; crop management; Crops; Decarbonization; Ecosystems; eddy covariance; Energy crops; Fluxes; Land resources; Land use; Longevity; Miscanthus; Oilseeds; Perennial crops; Plantations; Precipitation; Rape plants; Raw materials; Risk management; soil carbon; Soil surfaces; Soils; Stocks; Tillage; Wheat; Winter; United Kingdom > UK; United States > US
• ISSN: 1757-1693; 1757-1707
• DOI: 10.1111/gcbb.13114

Perennial bioenergy crops are a key tool in decarbonizing global energy systems, but to ensure the efficient use of land resources, it is essential that yields and crop longevity are maximized. Remedial shallow surface tillage is being explored in commercial Miscanthus plantations as an approach to reinvigorate older crops and to rectify poor establishment, improving yields. There are posited links, however, between tillage and losses in soil carbon (C) via increased ecosystem C fluxes to the atmosphere. As Miscanthus is utilized as an energy crop, changes in field C fluxes need to be assessed as part of the C balance of the crop. Here, for the first time, we quantify the C impacts of remedial tillage at a mature commercial Miscanthus plantation in Lincolnshire, United Kingdom. Net ecosystem C production based on eddy covariance flux observations and exported yield totalled 12.16 Mg C ha−1 over the 4.6 year period after tillage, showing the site functioned as a net sink for atmospheric carbon dioxide (CO2). There was no indication of negative tillage induced impacts on soil C stocks, with no difference 3 years post tillage in the surface (0–30 cm) or deep (0–70 cm) soil C stocks between the tilled Miscanthus field and an adjacent paired untilled Miscanthus field. Comparison to historic samples showed surface soil C stocks increased by 11.16 ± 3.91 Mg C ha−1 between pre (October 2011) and post tillage sampling (November 2016). Within the period of the study, however, the tillage did not result in the increased yields necessary to “pay back” the tillage induced yield loss. Rather the crop was effectively re‐established, with progressive yield increases over the study period, mirroring expectations of newly planted sites. The overall impacts of remedial tillage will depend therefore, on the longer‐term impacts on crop longevity and yields.
Remedial surface tillage has been proposed to improve Miscanthus yields by redistributing rhizomes and reducing canopy gaps, however, tillage is often associated with soil carbon losses. We studied remedial tillage in a commercial Miscanthus plantation and observed a temporary reduction in yield but no impact on soil carbon sequestration compared to a paired untilled site. Whole field eddy covariance measurements over a 5 year period confirmed that the plantation was a carbon sink (20.68 Mg C ha−1). Yield modelling estimated 12.16 Mg C ha−1 of this carbon remained within the plantation whilst 8.52 Mg C ha−1 was exported as harvested material.