Maize grown for bioenergy on peat emits twice as much carbon as when grown on mineral soil

The area of land dedicated to growing maize for bioenergy in the United Kingdom is rapidly expanding. To understand how maize production influences soil carbon (C) dynamics, and whether this is influenced by soil type, we measured net ecosystem exchange (NEE) using the eddy covariance technique over the 2021 growing season. We combined the NEE data with C imports and exports to calculate the net ecosystem productivity (NEP) of two maize crops grown for bioenergy in the United Kingdom, one site on mineral soil and the other on lowland agricultural peat. Maize was similarly productive at both sites—gross primary productivity was 1107 g C m−2 at the site with mineral soil and 1407 g C m−2 at the peat site. However, total ecosystem respiration was considerably higher from the peat site (1198 g C m−2) compared with the mineral soil site (678 g C m−2). After accounting for the removal of C in harvested biomass, both sites were net C sources, but C losses were over two times greater from the peat site (NEP = 290 g C m−2) than the mineral site (NEP = 136 g C m−2). While annual crops may be needed to produce bioenergy in the short term, growing maize for bioenergy in the United Kingdom does not appear to be a viable option for C sequestration over the long term, as it leads to high carbon losses from agroecosystems, especially those on organic soils. Instead, growing perennial bioenergy crops on mineral soils with a low organic C content is a more appropriate option. Net ecosystem exchange (NEE) of CO2 and net ecosystem productivity (NEP) of bioenergy maize were measured using the eddy covariance technique at two sites in the United Kingdom, one on mineral soil and one on peat, over the 2021 growing season. Higher total ecosystem respiration at the peat site, meant that NEE was more negative at the mineral site. NEP showed both sites to be net carbon sources, but carbon losses were over two times greater from the peat site (290 g C m−2) than the mineral site (136 g C m−2).