HAL Id: hal-01617684
https://hal.archives-ouvertes.fr/hal-01617684
Submitted on 3 Jun 2020
HAL is a multi-disciplinary open access
archive for the deposit and dissemination of
sci-entific research documents, whether they are
pub-lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.
L’archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d’enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.
Soil carbon sequestration in a Mediterranean
agroforestry system
Rémi Cardinael, Tiphaine Chevallier, Bernard Barthès, Christian Dupraz,
Claire Chenu
To cite this version:
Rémi Cardinael, Tiphaine Chevallier, Bernard Barthès, Christian Dupraz, Claire Chenu. Soil carbon
sequestration in a Mediterranean agroforestry system. 2. European Agroforestry Conference,
Euro-pean Agroforestry Federation (EURAF). INT., Jun 2014, Cottbus, Germany. 290 p. �hal-01617684�
Soil carbon sequestration in a Mediterranean agroforestry
system
Rémi Cardinael1,3*, Tiphaine Chevallier1, Bernard Barthès1, Christian Dupraz2, Claire Chenu3
*Corresponding author: remi.cardinael@supagro.inra.fr
1 IRD, UMR Eco&Sols, Montpellier SupAgro, Bâtiment 12, 2 place Viala, 34060 Montpellier, France 2 INRA, UMR System, Montpellier SupAgro, Bâtiment 27, 2 place Viala ,34060 Montpellier, France 3 AgroParisTech,UMR Bioemco, Bâtiment Eger, Avenue Lucien Brétignières, 78850 Thiverval-Grignon, France
Introduction
The Earth soils are a large reservoir of carbon (C), containing about 1500 PgC, which represents two to three times the C contained in the atmosphere. This reservoir is extremely sensitive to land use and can act as a source or as a sink of atmospheric carbon dioxide (CO2). Agroforestry
systems are expected to sequester C into both above and belowground biomass. Such systems could also increase soil organic carbon (SOC) stocks due to higher organic inputs including leaf litter, pruning residues, tree fine root turnover, and root exudates. However, although agroforestry systems have been thoroughly investigated in tropical regions, their potential for C sequestration has rarely been studied in temperate regions, and when studied, has mostly concerned superficial soil layers (Lorenz and Lal 2014). The objectives of this study were (i) to quantify the SOC stocks down to 2 m soil depth in an 18-year-old agroforestry system and in an adjacent agricultural plot, (ii) to study spatial distribution of SOC stocks, especially in relation to the distance from the trees, and (iii) to assess which SOC fractions are responsible for possible differences between treatments.
Material
The experimental field was established in 1995 in Prades-le-Lez (longitude 04°01’ E, latitude 43°43’ N, elevation 54 m a.s.l.), near Montpellier, South of France, on an alluvial carbonated Fluvisol. The climate is sub-humid Mediterranean with an average temperature of 14.5° C and an average annual rainfall of 951 mm (Mulia and Dupraz 2006). In the agroforestry system, hybrid walnut trees (Juglans regia x nigra cv. NG23) were planted at a density of 110 trees ha-1 (13 m between tree rows), and intercropped with a winter crop, mainly durum wheat (Triticum turgidum ssp. durum). In the adjacent agricultural plot, only the annual crop was cultivated. Spontaneous vegetation also grew on the tree rows. A first field sampling was realized in December 2012, and 24 soil cores were collected down to 2 m depth. Soil texture was analyzed, allowing to delimit two plots of 625 m2 each in the agroforestry field and in the control field, with the same soil texture. In May 2013, about 200 soil cores were sampled down to 2 m depth into these two plots. Each soil core was cut into ten layers, and bulk densities were measured for each of them, as well as texture and SOC contents, which were either analyzed conventionally (dry combustion after decarbonatation) or predicted using field visible and near infrared spectroscopy (Gras et al. 2013). Carbon stocks were spatialized at the field scale. To determine which SOC fractions were affected by the agroforestry system, soil particle-size fractionation (Gavinelli et al. 1995) was performed on 64 soil samples, collected at 0-10, 10-30, 70-100 and 160-180 cm soil depth.
Results
Soil carbon stocks were characterized by a high, but organized spatial variability. Spatial analysis showed twice higher SOC topsoil content on the tree rows compared to the inter-rows. Whereas the SOC stock in the reference agriculture plot was 42.29 ± 0.53 MgC ha-1 (0-30 cm) and 118.48 ± 0.88 MgC ha-1 (0-100 cm), in the inter-row significant additional storage of 2.5 ± 0.80 and 3.5 ± 1.29 MgC ha-1 was observed at 0-30 and 0-100 cm, respectively. On the tree row, additional storage was 17.5 ± 1.06 and 20.5 ± 1.50 MgC ha-1respectively,compared to the agricultural plot. Below 1 m depth, SOC stocks did not differ. Knowing that tree rows represent 16% of the agroforestry plot, we calculated the additional SOC storage of the whole field compared to the control plot. Annual additional SOC storage rates were estimated at 272 ± 68 kgC ha-1 yr-1 (0-30 cm) and 352 ± 98 kgC ha
-1 yr-1 (0-100 cm). This additional storage was mainly due to the particulate organic matter fraction
(50-200 and > (50-200 µm), whereas only 10 to 15% was associated to clay particles (< 2 µm). Total organic carbon storage rate would reach about 1.2 MgC ha-1 yr-1 when trees biomass was also taken into account.
Discussion
High SOC contents on the tree rows were mainly due to high inputs from the natural vegetation. No clear pattern of SOC content was observed in relation to the distance to the trees, but the tree row had an important impact on the SOC storage of the agroforestry field due to the spontaneous vegetation. This is an indirect effect of agroforestry systems: the tree row also acts as a permanent pasture, and has a positive impact on SOC sequestration. Additional SOC storage rates are higher than those commonly reported for other techniques used to improve SOC in agriculture, such as no-till farming or conservation agriculture (Pellerin et al. 2013). Up to now, additional storage is mainly limited to topsoil layers and in labile organic fractions, making it an unstable storage.
References:
Gavinelli E, Feller C, Larré-Larrouy M., et al. (1995) A routine method to study soil organic matter by particle-size fractionation: examples for tropical soils. Commun Soil Sci Plant Anal 26:1749–1760.
Gras J-P, Barthès BG, Mahaut B, Trupin S (2013) Best practices for obtaining and processing field visible and near infrared (VNIR) spectra of topsoils. Geoderma 214-215:126–134.
Lorenz K, Lal R (2014) Soil organic carbon sequestration in agroforestry systems. A review. Agron Sustain Dev 34:443–454. Mulia R, Dupraz C (2006) Unusual fine root distributions of two deciduous tree species in southern France: What consequences
for modelling of tree root dynamics. Plant Soil 281:71–85.
Pellerin S., Bamière L., Angers D., Béline F., Benoît M., Butault J.P., Chenu C., Colnenne-David C., De Cara S., Delame N., Doreau M., Dupraz P., Faverdin P., Garcia-Launay F., Hassouna M., Hénault C., Jeuffroy M.H., Klumpp K., Metay A., Moran D., Recous S., Samson E., Savini I., Pardon L., 2013. Quelle contribution de l’agriculture française à la réduction des émissions de gaz à effet de serre ? Potentiel d'atténuation et coût de dix actions techniques. Synthèse du rapport d'étude, INRA (France), 92 p.
