Effective climate change mitigation through cover cropping and integrated fertilization: A global warming potential assessment from a 10-year field experiment

Abstract

Abstract In this study, field-specific data was collected from a 10-year experiment in central Spain in which vetch (Vicia sp. L.) and barley (Hordeum vulgare L.) were established as cover crops and compared to the traditional fall-winter fallow between two irrigated cash crops, maize (Zea mays L.) and sunflower (Helianthus annuus L.). The global warming potential (GWP) balance included direct and indirect (nitrous oxide (N2O) resulting from the deposition of ammonia (NH3) or from leached nitrate (NO3−)) soil greenhouse gas (GHG) emissions, changes in soil organic carbon (SOC) and albedo, and carbon dioxide equivalent (CO2eq) emissions from inputs, irrigation and farm operations. Several scenarios involving i) changes in the termination method of the cover crops, ii) consideration of the application of a distinct nitrogen (N) source (urea, slurry or manure instead of ammonium nitrate) or nitrification inhibitors, iii) employing the same N rate for all treatments (i.e., conventional instead of integrated fertilization), iv) modelling SOC accumulation over a 100-year horizon, and v) using default emission factors, were also analysed. Under the conditions of our experiment, cover crops mitigated yield-scaled emissions by 77.4% (barley) and 91.9% (vetch). Synthetic N fertilization (particularly the industrial production of fertilizer) contributed 38% to the balance of the cover cropping treatments, followed by SOC (22.5%), irrigation (14.7%) and albedo (14.5%). All scenarios led to notable mitigation efficacies, ranging from 39% mitigation (in barley when considering default or non-specific emission factors) to a net CO2eq sink (i.e., >100% mitigation) in the scenario consisting of the replacement of ammonium nitrate by urea or organic fertilizers although with side effects on NH3 volatilization and/or yields. Based on these results, the combined use of cover cropping and integrated soil fertility management could lead to the design of C-neutral irrigated cropping systems in semi-arid regions.