The hidden carbon in the sand-size fraction

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Abstract

Despite the importance of SOM and extensive studies, key gaps remain in understanding the distribution of mineral-associated organic carbon (MAOC) and particulate organic carbon (POC) fractions. This study quantifies the effects of contrasting agronomic field crops practices, till (conventional) and no-till with service crops (conservation), on soil organic carbon (SOC) content and its fraction distribution along soil depth (0–60 cm) located at the Model Farm for Sustainable Agriculture (high clay soil, Usters). SOC fractions were assessed using combined density and size fractionation to isolate particulate organic matter (POM), and sand, silt and clay size particles, alongside measurements of C, N, labile carbon, and aggregate stability. By linking SOC dynamics to management decisions, this study aims to advance understanding of carbon stabilization mechanisms and support strategies to enhance soil health, resilience, and long-term carbon sequestration. Preliminary results show, as expected, declining SOC with depth. MAOC and inorganic carbon concentrations were higher under conservation practices. In addition, there is a slightly higher total and labile SOC in topsoil under conservation, accompanied by higher aggregate stability. POC was minimally affected by treatment. Notable proportion of MAOC (~13%) was, unexpectedly, associated with the sand-sized fraction, indicating that in addition to the commonly measured MAOC in the silt and clay fraction, the sand-size fraction should be considered. Finally, this observation suggests that additional pathways for carbon stabilization, occur under long-term management.

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Programme
10:30 to 11:00 on 05/26/2026
COMMON AREA
Institutions
  • 1 Hebrew University of Jerusalem
  • 2 Ministry of Agriculture and Food
Track
  • Best management practices for SOM (cropland, pasture, forestry)
Keywords
Soil Organic Matter
Mineral Associated Organic Carbon
Conservation Agriculture
Soil Health
Soil Organic Carbon