Guiding soil carbon sequestration with a novel organic material returning index globally

Straw returning (SWR) and manure returning (OMR) are vital for enhancing soil organic carbon (SOC) sequestration in croplands, supporting agricultural sustainability and climate change mitigation. We developed the Organic Material Returning Index (OMRI) using data from 347 global cropland sites to guide OMR and SWR selection. Our findings show OMR increases SOC by 35.60% in low-SOC soils compared to 13.92% for SWR, driven by initial SOC and soil pH, while SWR dexcels in low-clay soils (<18%) and warmer climates, governed by clay content and mean annual temperature. The OMRI (threshold k=0.2874) identifies 27.8% of croplands, notably in mid-to-high latitudes (e.g., Canada, Northeast China) and equatorial regions (e.g., West Africa), as suitable for cost-effective SWR, outperforming machine learning’s 2.38% prediction. Unlike opaque models, the OMRI offers a transparent, mechanistically grounded framework, enabling region-specific strategies to maximize SOC sequestration and inform sustainable agricultural policies worldwide.