Contribution of tree and crop roots to soil carbon stocks in a Sub-Sahelian agroforestry parkland in Senegal

Siegwart Lorène, Bertrand Isabelle, Roupsard Olivier, Jourdan Christophe. 2023. Contribution of tree and crop roots to soil carbon stocks in a Sub-Sahelian agroforestry parkland in Senegal. Agriculture, Ecosystems and Environment, 352:108524, 11 p.

Résumé : In the Sub-Sahelian region (Senegal), Faidherbia albida trees have been maintained for years in agroforestry parklands for their numerous services offered to people and to crops. The aerial crop biomass and yield are notably greater under the tree crown, but most of this biomass is exported and does not contribute to soil carbon (C) inputs. Belowground litter inputs are crucial, but little is known about the root system distribution, productivity and contribution to soil C inputs. This study aims to assess the field heterogeneity of F. albida and crop root systems along the soil profile based on the distance to the tree to evaluate the root contribution to soil C stocks. During two successive rotations of pearl millet in 2020 and groundnut in 2021, soils and roots were sampled from two locations (Under and Far from the tree), in 5 soil layers to a depth of 150 cm and with three tree replicates. The aerial biomass was also sampled. The annual relative contribution of roots to soil C stocks was estimated as the ratio between root litter-derived C inputs (considering hypothetical root turnover only for trees and the whole root biomass for crops) and soil C stocks. We found a similar crop root biomass density Under and Far from the tree, but the higher root:shoot ratio Far from than Under the tree confirmed the beneficial effect of trees on the aerial crop biomass. Unexpectedly, the tree root biomass density was higher at + 30 m from the trunk than Under the tree in the 30–100 cm soil layer, suggesting a long-distance soil exploration by the trees. Down to 150 cm of depth, the tree root litter contribution to soil C stocks represented 6.1 % and 7.1 % of the total root litter-derived C inputs (Under and Far from the tree, respectively). In this type of Sub-Sahelian parklands with low soil C stocks, increasing the tree density or selecting deep and highly rooted crop varieties should be favoured.

Mots-clés Agrovoc : système racinaire, agroforesterie, biomasse, racine, Faidherbia albida, enracinement, rhizosphère, plante racine, compétition interspécifique, rendement des cultures, propriété physicochimique du sol, profondeur

Mots-clés géographiques Agrovoc : Sénégal

Mots-clés libres : Faidherbia albida, Groundnut, Pearl millet, Root litter-derived C, Soil C stocks, Soil depth

Classification Agris : P33 - Chimie et physique du sol
P34 - Biologie du sol
F08 - Systèmes et modes de culture

Champ stratégique Cirad : CTS 2 (2019-) - Transitions agroécologiques

Agences de financement européennes : European Commission

Agences de financement hors UE : Agropolis Fondation, Total Foundation

Projets sur financement : (EU) EU-LEAP-Agri RAMSES I, (FRA) DSCATT

Auteurs et affiliations

• Siegwart Lorène, CIRAD-PERSYST-UMR Eco&Sols (FRA)
• Bertrand Isabelle, INRAE (FRA)
• Roupsard Olivier, CIRAD-PERSYST-UMR Eco&Sols (SEN)
• Jourdan Christophe, CIRAD-PERSYST-UMR Eco&Sols (FRA) ORCID: 0000-0001-9857-3269 - auteur correspondant

Source : Cirad-Agritrop (https://agritrop.cirad.fr/608198/)

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