Agroforestry olive orchards for soil organic carbon storage: Case of Saiss, Morocco

Abstract

Soil supports numerous ecosystem services and contributes to climate change mitigation. Several publications have appeared in recent years considering soil as a persistent carbon sink and reported that agroforestry systems have a potential for soil organic carbon storage. However, there is still little knowledge about the soil organic carbon storage in olive orchards and its role in climate change mitigation. Therefore, soil samples collected from topsoil (0-30 cm) and subsoil (30-60 cm) in 57 different olive orchards provide an excellent opportunity to investigate the role of several factors (tree ages, planting density, farming system type and soil depth) in driving soil organic carbon storage variability in agroforestry olive orchards compared to olive trees in monoculture system across the Saiss region (Morocco). The difference was significant between the two types of plantation systems studied (agroforestry and monoculture) and between the two soil layers studied (topsoil and subsoil). Agroforestry olive orchard systems stored approximately 1.2 times the organic carbon in the soil compared to monoculture systems. In addition, topsoil stores 1.5 times compared to subsoil. The correlation results showed a positive relationship between the organic carbon stock of the topsoil and the subsoil, indicating that an increase in the topsoil is accompanied by an increase in the organic carbon stock of the subsoil. These results can provide a better understanding of the effect of agroforestry on deep soil organic carbon stock in Moroccan olive orchards. Furthermore, it can provide a valuable reference for future research on the soil organic carbon storage variability in Morocco and from an international perspective.

Keywords: Agroforestry; Climate change mitigation; Morocco; Olive groves; Soil organic carbon stock; Subsoil; Topsoil.

Fig. 1

Map showing the geographical location of the study area in Morocco (A), in the Fes-Meknes region (B), and the geographical location of surveyed olive orchards in the study area (C).

Fig. 2

Mean monthly precipitation and air temperature of the study area. Data source: NASA, https://power.larc.nasa.gov/beta/data-access-viewer/(from 2012 to 2022).

Fig. 3

Soil map of the study area. Data source: FAO, https://data.apps.fao.org/map/catalog/srv/eng/catalog.search#/metadata/446ed430-8383-11db-b9b2-000d939bc5d8.

Fig. 4

Soil organic carbon stock in 0–60 cm soil depth in different olive groves age classes. The boxplots range from the first to the third quartile where the horizontal line shows the median. The vertical lines go from each quartile to the minimum or maximum, respectively.

Fig. 5

Soil organic carbon stock in 0–60 cm soil depth in different olive groves planting density. The boxplots range from the first to the third quartile where the horizontal line shows the median. The vertical lines go from each quartile to the minimum or maximum, respectively.

Fig. 6

Soil organic carbon stock in 0–60 cm soil depth in agroforestry and monoculture olive orchards. The boxplots range from the first to the third quartile where the horizontal line shows the median. The vertical lines go from each quartile to the minimum or maximum, respectively.

Fig. 7

Soil organic carbon stock of topsoil and subsoil. The boxplots range from the first to the third quartile where the horizontal line shows the median. The vertical lines go from each quartile to the minimum or maximum, respectively.

Fig. 8

Correlation between soil organic carbon stock in topsoil (0–30 cm) and soil carbon stock in subsoil (30–60 cm) of whole olive orchards studied.

Fig. 9

Soil organic carbon stock by olive groves density in 0–60 cm soil depth in agroforestry and monoculture systems. Values are mean ± SE.