Agronomic management strategies to increase soil organic carbon in the short-term: evidence from on-farm experimentation in the Veneto region

Background and aims: Organic fertilizers and cover crops (CC) are considered crucial strategies to pursue the objective of increasing soil organic carbon (SOC). The present research focuses on an ‘on farm experimentation’ to assess the combined effects of organic fertilization with different biomasses, CC and irrigation on SOC stock. Methods: A 4-year on-farm experimentation was co-developed with local farmers and a land reclamation authority in north-eastern Italy on a biennial maize-soybean rotation. We examined the effects of two organic fertilizers (compost or digestate), three CC treatments (a fixed cover crop species – x triticosecale; a succession of cover crop species – Sinapis alba and Lolium multiflorum; no CC) under rainfed and irrigated conditions on the SOC content and stock, and crops yields. Results: All these integrated practices – except when digestate was applied in the field in the absence of a CC under rainfed conditions – determined a significant increase of the SOC stock after 4 years, matching the goals set by the ‘4 per mille’ initiative. The highest SOC increase was observed under irrigated management and compost fertilization, regardless of the presence or absence of a CC (range: 9.3–10.3 Mg ha−1 in the first 0–40 cm of soil). Soybean grain yields were comparable with those obtained in farms of the same rural district under business as usual, but maize grain yields were lower. Conclusion: SOC accumulation is achievable in the short term with abundant applications of organic biomass, but the strategy might lead to economic loss such as lower maize productivity.