Carbon saturation and assessment of soil organic carbon fractions in Mediterranean rainfed olive orchards under plant cover management

Abstract

Olive groves are undergoing a marked change in the way that inter-row land is managed. The current regulation and recommendation encourages the implementation of plant cover, mainly to improve soil fertility and reduce erosion. However, there is no quantitative information on the dynamics and pools of soil organic carbon (SOC) fractions of different protection levels of the plant-residue-derived organic carbon (OC). This study was conducted to provide a range of annual OC inputs in commercial olive oil groves under natural plant cover, to assess the influence of the annual application of aboveground plant cover residues on unprotected and physically, chemically and biochemically protected SOC. In addition, we tested the carbon saturation hypothesis under plant cover. Ten olive oil orchards under plant cover management (PC), together with five comparable bare soil olive oil orchards (NPC) were selected and annual aboveground natural plant residues and SOC pools were sampled and quantified. Annual aboveground plant cover biomass and OC production in PC olive orchards averaged 1.48 t dry-weight (DW) ha-1 and 0.56 t C DW ha-1, respectively with a great variability among sites (coefficient of variation of about 100 %). SOC concentration in PC orchards was, on average, 2.8 (0 -5 cm soil) and 2.0 (5 -15 cm) times higher than in bare soils of NPC, and the pool of protected SOC in the top 15 cm was 2.1 times higher in the PC (17.9 mg C g-ndard deviation) compared to NPC (8.5 mg C golive orchards. Linear or saturation type relationships between each SOC fraction and total SOC content for the range of SOC of the commercial olive oil orchards were statistically indistinguishable, and thus linear models to predict SOC accumulation due to plant cover in olive orchards are suitable, at least for the studied range of SOC. Overall, at regional scale where olive oil groves represent a very high proportion of the agricultural land, the use of plant cover appears to be a promising practice that promotes protection of the SOC, thus improving SOC sequestration.

Changes in soil organic carbon under perennial crops

“…(2011), but this merely reflects the large weighting of BD in the calculation of SOC density. Soils with higher BD and lower SOC content are likely to have higher saturation deficit (Six, Conant, Paul, & Paustian, 2002)—the difference between maximum and minimum SOC that could be achieved—and thus may have higher potential to increase the SOC stocks (Vicente‐Vicente, Gómez‐Muñoz, Hinojosa‐Centeno, Smith, & Garcia‐Ruiz, 2017). The cultivated crop is a confounding factor in this study, and even with more data this limitation may remain, since some crops have a limited environmental range and are therefore only cultivated in certain climates.…”

“…The physical protection (i.e., organic C within soil microaggregates) isolates the organic C from the activity of the soil microorganisms, preventing its mineralization. SOC physical protection is also affected by tillage (Vicente‐Vicente et al., 2017), because of the disruption of the macroaggregates, precursors of soil microaggregates (Six, Bossuyt, Degryze, & Denef, 2004). This may be another mechanism that favors SOC accumulation under perennial crops, due to the lack of mechanical intervention.…”

Estimation of Soil Organic Carbon Storage in Palustrine Wetlands, China

“…Additionally, from cold temperate zones to the tropical zones, vegetation respiration increases, as seen in the results from the C3, C4, and C7 geographical regions which showed lower SOC content than that in the C1 geographical region. Explicitly, SOC storage in marsh is dominated by the amount of vegetation litter and decomposition [ 50 ].…”

Organic carbon pools and storage in the soil of olive groves of different age

“…For this reason, recent EU environmental strategies applied to both research and policy have focused on agricultural management options that can ensure food productivity whilst improving soil quality, reducing impact on the environment and enhancing climate mitigation (Council of the European Union, ). To this aim, conservation soil management strategies, such as minimum or no tillage, permanent grass cover (Agnelli et al ., ; Vicente‐Vicente et al ., ), increasing crop residues returned to the field (Gómez‐Muñoz et al ., ), improved crop rotation and organic rather than mineral fertilization, have been identified as potentially successful options to reduce C losses and increase SOC stabilization and storage (Paustian et al ., ). Therefore, studies that analyse the effect of agricultural management on the soil C sink should consider not only the amount of C stored in the soil but also its stability.…”