Aims <p>High demand for biomass to substitute fossil fuel-based products may be served via straw removal at large scale with unknown consequences for soil organic carbon (SOC). Aim of this study was to quantify the SOC effect of additional straw removal in German croplands.</p> Methods <p>In three scenarios (business-as-usual, 50% and 100% additional straw removal), we modelled SOC effects of increased straw removal on 1,115 field sites from the first German Agricultural Soil Inventory using site-specific soil and management data. We applied a model ensemble combining three allometric approaches with the model RothC.</p> Results <p>Annual straw harvest from German croplands could be tripled to 26.3 Tg straw (dry matter). Currently, straw is mainly harvested for animal husbandry and returned to soils together with farm yard manure (9.0 Tg straw). Removing all additionally harvestable straw (17.4 Tg straw) would decrease mean carbon (C) inputs to German croplands by 21%. Within 20&#xa0;years, SOC stocks would decrease by 0.10 ± 0.20&#xa0;Mg C ha⁻¹ a⁻¹, corresponding to emissions of 4.2 Tg CO₂ a⁻¹ at national scale compared to business-as-usual. Modelled losses decreased over time but persisted even after 200&#xa0;years. Relative SOC loss per Mg straw removed was larger on clayey soils compared to sandy soils.</p> Conclusions <p>Harvesting additional straw will result in SOC losses which may offset efforts to reduce greenhouse gas emissions via fossil-fuel substitution. A climate-smart residue management needs to include compensation strategies such as cover cropping in order to maintain SOC levels and mitigate climate change.</p>