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Aims: Soil organic carbon (SOC) stocks of croplands can be enhanced by targeted management, which boosts soil fertility and contributes to climate change mitigation. One SOC sequestration option is adopting cover crops. The aim of this study was to quantify the SOC sequestration potential of cover crops in Germany. Methods: We simulated SOC scenarios on 1,267 cropland sites with site-specific management data using an SOC model ensemble consisting of RothC and C-TOOL. A new method was developed to estimate carbon input from cover crops that included the effects of climate, sowing date and species on cover crop biomass production. Results: The recent cover crop area could be tripled to 30% of arable land in Germany. This would enhance total carbon input by 12% and increase SOC stocks by 35 Tg within 50 years, corresponding to an annual increase of 0.06 Mg C ha-1, 2.5 Tg CO2 or 0.8 per mill of current SOC stocks in 0–30 cm depth. On sites with cover crops, 0.28–0.33 Mg C ha-1 a-1 would be accumulated within 50 years. Our simulations predicted that even if the full potential for cover crop growth were realised, there would still be a decline in SOC stocks in German croplands within 50 years due to the underlining negative SOC trend. Conclusions: Cover crops alone cannot turn croplands from carbon sources to sinks. However, growing them reduces bare fallow periods and SOC losses and thus is an effective climate change mitigation strategy in agriculture. [ABSTRACT FROM AUTHOR]

Oil palm dominates global oil production, trade, and consumption. Nigeria is one of the leading palm oil producers and consumers. A significant challenge of the palm oil industry is to reduce the environmental impacts (e.g. pollution and carbon footprint) and integrate a circular economy in operation. This study aims to comparatively quantify the environmental impacts of technologies used by different mills. We applied a life cycle assessment in the case of Nigeria. The study covers the reception and processing of fresh fruit bunch (FFB) to end-product palm oil. The inputs include generated empty fruit bunch (EFB), mesocarp fibre, palm kernel shell, palm oil mill effluent, diesel, water and all outputs to the environment for a functional unit of 1-tonne FFB. The results showed that large-scale mills perform worse (468 kg CO2-eq per t FFB) than the semi-mechanised and smallholder mills in effects on climate change but better in the other impact categories, including human toxicity, ecotoxicity, and fine particulate matter formation. In large-scale mills, the climate change impacts decrease by 75% when the raw palm oil mill effluent (POME) is used in composting EFB. Similarly, climate change impacts reduce by 44% when biogas from POME substitutes diesel in the semi-mechanised and smallholder mills. We conclude that regulatory measures are needed to ensure improved management practices in the production processes. Particular attention should be paid to the generation and reuse of biomass and POME. This study provides a handy reference to assist the sustainable energy transition in Nigeria's and other parts of sub-Saharan Africa's oil palm industry to mitigate climate change and form a cleaner bioeconomy. [ABSTRACT FROM AUTHOR]