Soil management effects on soil organic matter properties and carbon sequestration (SOMPACS)

Purpose

SOMPACS is a project recommended by EJP SOIL for funding under the 1st External Call "Towards Healthy, Resilient and Sustainable Agricultural Soils". The purpose of SOMPACS is to disclose management practices enriching soils with the organic matter pools that are most resistant to microbial decomposition. The project started in 2022 and will be implemented by a consortium of 12 research institutions from Poland, Germany, Ireland, Lithuania, UK, Italy and the USA until 2025.

Methods

Soil samples from eight long-term field experiments with different soil management and cultivation systems (conventional tillage vs. no-tillage; mineral vs. organic fertilization; management with and without catch crop; arable land vs. grassland; and cultivated vs. non-cultivated soils) will be investigated. Field experiments will include trials of increasing duration: 22-year (Lithuania); 26-year (Italy); 30-year (Poland, Ireland); 46-year (Poland); 54-year (Lithuania); 100-year (Poland), and 178-year Broadbalk experiment (UK). Experiments will also be carried out in production fields, where additives that stimulate root growth and provide very stable C (commercial humic products, biochar, and biogas digestate) will be applied. The effects of these additives on the content and properties of SOM will be investigated also in experimental plots accompanied by the incubation studies on the microbial decomposition of SOM and these additives. In parallel with soil sampling, plant productivity will be measured in all field experiments. Basic soil properties will be supplemented by the following investigations based on state-of-the-art approaches: SOM composition and stability by Py-GC-MS; aggregate size classes and C pools of increasing physicochemical protection; analysis of δ¹³C and δ¹⁵N of the separated SOM pools; microbiological properties (community-level physiological profiling, selected functional genes involved in C and N cycles, microbiome and mycobiome analyzes by next-generation sequencing, genetic diversity using terminal restriction fragment length polymorphism);  enzymatic activity; soil water retention and soil water repellency; mineral composition of clay fraction; soil structure stability. The most resistant SOM pool (humin) will be isolated by different methods (isolation vs. extraction) and examined for chemical composition and structure, using spectrometric and spectroscopic techniques (mass spectrometry, NMR, FTIR, EPR, UV-Vis-NIR, fluorescence). The C stocks in the soil profile will be evaluated and the extractable C in cold water will be determined to assess the potential leaching and microbial availability of C. Additionally, CO₂ emissions from the soil of chosen experiments will be measured directly under field conditions.

Results

In the first stage of the research, soil samples were collected from a depth up to 100 cm and the humin fraction from surface horizons was isolated for spectroscopic studies. Meantime, the impact of various types of cultivation on the yield was determined. 

Conclusions

A closer understanding of the persistence of SOC in top- and subsoil, as well as identifying management practices that contribute to minimizing greenhouse gas emissions, will show the possibilities of increasing the stable SOM pools, thus improving the potential of C sequestration. Understanding the impact of soil management on sustainable agricultural production and the environment, and in particular on climate change mitigation, should be widely promoted and put into practice.

Project partly financed by NBCR (project EJPSOIL/I/78/SOMPACS/2022).