Effects of long-term residue return on nutrient content, ecological and economic benefits of black soil in Northeast China

Improved tillage practice plays a positive role in restoring degraded cropland, maintaining crop productivity, and mitigating climate change, which has been proposed as a sustainable agricultural technology. Based on a long-term experiment in black soil area of Northeast China, effects of different tillage practices on soil organic carbon (SOC) and nutrient content were explored, and ecological and economic benefits were also evaluated. Three tillage practices were included: conventional tillage with complete removal of residue (CT), moldboard plowing with residue return (MP) and no-tillage with residue return (NT). As the trial period increased, the SOC content of the CK decreased in the 0-20 cm soil layer, while the total nitrogen (TN) content remained. Residue return treatments (MP and NT) increased SOC and TN content. The SOC and TN were uniformly distributed in the 0-20 cm soil layer of MP, whereas the SOC and TN increased significantly in the 0-5 cm soil layer of NT, especially during the 5-8 years of the experiment. The total phosphorus (TP) and total potassium (TK) contents of all treatments slowly increased over time, and there was no significant difference among treatments. Compared with CT, NT could reduce N₂O emissions and absorb more CH₄, whereas MP significantly increased CO₂ emissions from soil. Moreover, NT led to both the lowest GHG emissions from soil (GWP_GHG) and agricultural inputs (AIGHG), thus reduced approximately 40% carbon footprint (CF) compared to CT. However, no significant difference in maize yield and net ecosystem ecological benefit (NEEB) were observed among three tillage practices, although MP and NT showed lower investments during maize production than CK. In conclusion, NT could not only enhance the SOC and nutrient content but also minimize CF while ensuring economic benefit from a long-term perspective. Long-term NT can be implemented in Northeast China and similar agro-eco-regions around the world.