In a collaborative study published in Nature Communications on March 2, researchers from the Institute of Applied Ecology of the Chinese Academy of Sciences reported that agricultural management intensity plays a key role in regulating the soil priming effect and, in turn, long-term soil carbon dynamics.

Soil priming effect refers to the changes in the rate at which native soil organic carbon decomposes following the addition of fresh carbon inputs, such as plant residues or organic materials like manure and compost. This process is considered an important component of the global carbon cycle because it determines whether soils act as sources or sinks of carbon. Although the impact of agricultural practices on soil organic carbon is widely studied, the effect of management intensity on priming processes over long timescales and across broad geographic gradients is less understood.

To address this gap, ZHANG Weidong's team, in collaboration with international partners including the Spanish National Research Council (CSIC), analyzed soils from eight long-term experimental sites spanning three major climate zones in Europe. These sites are part of the Long-Term Experiments network, which provides consistent observations of agricultural soils under different management regimes. 

The researchers classified the soils into four levels of management intensity based on tillage practices and types of fertilization. They then applied a carbon-13 isotope tracing method to quantify the magnitude and direction of the priming effect under each condition. The isotope tracing approach allows scientists to distinguish between newly added carbon and pre-existing soil carbon, thereby enabling precise estimation of changes in carbon mineralization.

The researchers found that the priming effect is strongly associated with soil carbon content across European croplands. They reported that low-intensity management practices, such as organic fertilization and reduced or no tillage, significantly enhanced the priming effect. In these systems, values of the priming effect were substantially higher, at around 10 micrograms of carbon per gram of soil. 

In contrast, high-intensity practices, including the exclusive use of chemical fertilizers and conventional tillage, reduced the priming effect. In some cases, they led to a negative priming effect with values near three micrograms of carbon per gram of soil. A negative priming effect indicates a slowdown in the decomposition of existing soil carbon following the addition of new carbon.

Further analysis showed that management intensity influenced the priming effect both directly and indirectly. Direct effects were associated with changes in soil organic carbon content, while indirect effects were linked to shifts in soil aggregate stability and soil microbial biomass. The researchers also identified several key predictors of priming dynamics, including the carbon-to-phosphorus ratio, total soil organic carbon, total nitrogen, and the activity of β-glucosidase, an enzyme involved in the breakdown of organic matter.