CAPTURE- Assessment of cover cropping as climate action in cereal production in Norway

Summary

Recently, the role of cover crops in agriculture has broadened due to their ecosystem services and their potential as a climate mitigation tool via carbon sequestration. However, their net climate effect from carbon sequestration may be offset by nitrate leaching and nitrous oxide (N2O) emissions when plant residues decompose in the soil. In CAPTURE (a 3-year project funded by the Agriculture and Food Industry Research Funds), we evaluate the net climate effect of different cover crops in the main cereal production areas in South and Mid-Norway. To determine the soil carbon sequestration potential from different cover crops, four species (Italian ryegrass, phacelia, oilseed radish and summer vetch) were planted in monoculture (in 4 replicates) in spring 2021 and pulse labelled (5-6 pulses) with 13CO2 during the growing season in 1 m3 transparent chambers. Shortly after the last pulse, biomass (above- and belowground) and soil samples were collected and brought to the laboratory for processing. These samples are now under analysis and together with consecutive samplings in 2022 we will determine the input of cover crop-derived carbon (13C) to the soil. These data will also be used to feed a model to evaluate the potential for long-term carbon storage of different cover-crops. Moreover, we will investigate the fate and persistence of this carbon input, by assessing how much of the 13C was retained as particulate organic matter (POM) and as mineral-associated organic matter (MAOM). The fate of soil organic matter -13C in each fraction will be monitored in the following years. To study the contribution of shoot- versus root biomass to carbon sequestration, we established microplots in which aboveground biomass was exchanged and incorporated reciprocally between the labelled microplot and an equivalent unlabelled microplot with the same cover crop. In this way, each field replicate includes one microplot with labelled shoots and unlabelled roots and another microplot with unlabelled shoots and labelled roots, which will be sampled and analysed in 2022. Cover crop-specific carbon sequestration will be scaled to barley plots in the same experiment, to which cover crops had been undersown in spring or summer 2021. In these plots, N2O emissions have been quantified weekly throughout the growing period and more frequently during autumn and winter, which should allow us to estimate greenhouse gas trade-offs of cover crops in Norwegian cereal production and contribute to improve the national greenhouse gas inventory.