Two Amendments, Two Pathways

Maintaining soil organic carbon is important for agricultural productivity and climate mitigation, yet organic amendments do not necessarily build soil carbon in the same way. A 10-year maize field experiment at Shenyang Agricultural University compared annual biochar application at 2.625 t ha⁻¹ with maize stover incorporation at approximately 7.5 t ha⁻¹, alongside an untreated control. The field plots received the treatments for ten consecutive crop seasons before soil was sampled at depths of 0–20, 20–40, and 40–60 cm.

Both amendments significantly increased soil organic carbon across the 0–60 cm profile. In the topsoil, carbon gains were similar for biochar and stover, at 49.70% and 48.87%, respectively. Stover produced larger increases in subsurface and deep-soil carbon, reaching 105.90% in the 20–40 cm layer and 32.35% in the 40–60 cm layer. Biochar produced corresponding increases of 72.81% and 4.74%. These contrasting depth patterns indicate that carbon accumulation depends on amendment-specific transport and stabilization processes.

A Food-System Carbon Shift

Tropical islands support important terrestrial and coastal carbon stores while facing strong pressures from development, land conversion, tourism, and climate change. In Hainan Island, food production, aquaculture, processing, and associated supply-chain activities have become increasingly important sources of greenhouse gas emissions within a rapidly developing regional economy.

Authors Zichen Li, Zhaohai Bai, and colleagues from Hainan University, the Chinese Academy of Sciences, and Nanjing University reconstructed the carbon budget of Hainan's food system from 1952 to 2020. Their life cycle assessment framework incorporated offshore ecosystems, land-use and land-use change, crop cultivation, livestock, aquaculture, food processing and consumption, wastewater treatment, and on-farm and off-farm energy use.

Seven Decades of Rising Emissions

Gross food-system emissions increased from 3.29 Mt CO₂ eq in 1952 to 15.13 Mt CO₂ eq in 2020. The analysis attributes this rise principally to fertilizer-related emissions, expansion of tropical crop cultivation, aquaculture growth, and increased energy demand along the food value chain. Nitrogen fertilizer application increased from 223 kg ha⁻¹ to 627 kg ha⁻¹ over the historical period.

A Changing Carbon Balance

Soil organic carbon supports soil health, water retention, nutrient cycling, soil structure, and microbial diversity. A review led by Nanthi Bolan examines how climate change-induced droughts, floods, and wildfires can alter these functions by changing carbon inputs, decomposition, erosion, and the movement of dissolved organic carbon.

The analysis places soil carbon within the wider climate system. Depending on environmental conditions and land management, soils can either store carbon or contribute to greenhouse-gas emissions. The authors argue that protecting soil carbon is important not only for climate mitigation but also for sustaining agricultural productivity and ecosystem services.

Mapping the Evidence

On 14 January 2026, the authors searched Google Scholar, PubMed, and Web of Science using terms related to climate change, extreme weather, soil carbon, microbial activity, decomposition, erosion, dissolved organic matter, and leaching. The initial search produced 14,218 records. After duplicate removal and eligibility screening, 3,754 articles were retained for bibliometric and qualitative analysis.