Comparing on-farm and long-term research experiments on soil carbon recovery by conservation agriculture in Southern Brazil

Global studies, generally, and Brazilian studies, specifically, on soil organic carbon (SOC) in experimental research plots, support conservation agriculture (CA) as a tool to partially or totally restore SOC stocks depleted by conventional tillage agriculture. In response, the Brazilian Government implemented in 2010-2030 a Low Carbon Agriculture Plan (ABC Plan) program centered on large-scale CA adoption. However, the projections of SOC recovery based on long-term research trials may not adequately portray farm level high-yield operations. The objectives of this study were: (a) quantify and compare SOC stocks to a 1-m depth in long-term CA at the farm scale (>20 years) with paired native vegetation and nearest available long-term research experiments (>30 years) in Southern Brazil; (b) explore the role of oilseed radish (Raphanus sativus L.) as a cover crop to enhance SOC accumulation. In general, farm level CA systems restored SOC at an equal or higher level than the paired research plots. For the farm level CA systems, average SOC recovery was 92% (0-0.30 m) and 97% (0-1.0 m) in the soil profile relative to native vegetation. Moreover, compared to research scale CA, farm level CA average SOC recovery was 91 and 86%, for the same soil layers. Recovery of SOC in research scale CA can be scaled up to farm level systems in Southern Brazil. The main characteristics for SOC recovery (0-1.0 m) were high inputs of plant biomass, lack of soil disturbance, and diversification with oilseed radish cover crop.

Automated summary

Global and Brazilian studies have shown that conservation agriculture can help restore soil organic carbon stocks depleted by conventional tillage. A farm-scale study in Southern Brazil found that conservation agriculture systems performed as well as or better than research plots in terms of soil organic carbon recovery, with high plant biomass inputs, minimal soil disturbance, and oilseed radish cover crops playing key roles.