Diachronic assessment of soil organic C and N dynamics under long-term no-till systems in the tropical upland of Cambodia

Leng Vira, Cardinael Rémi, Tivet Florent, Seng Vang, Mark Phearum, Lienhard Pascal, Filloux Titouan, Six Johan, Hok Lyda, Boulakia Stéphane, Briedis Clever, De Moraes Sa Joao Carlos, Thuries Laurent. 2024. Diachronic assessment of soil organic C and N dynamics under long-term no-till systems in the tropical upland of Cambodia. . UM6P, Chair of Soil Sciences, AITTC. Ben Guerir : UM6P, Résumé, 2 p. International Symposium on Soil Organic Matter (SOM2024). 9, Ben Guerir, Maroc, 26 Mai 2024/31 Mai 2024.

Résumé : We quantified the changes in soil organic carbon (SOC) and total nitrogen (N) stocks and forms to 100 cm depth from three 13-year-old experiments in a tropical red Oxisol in Cambodia, comparing conventional tillage (CT) and different no-till (NT) cropping systems using a diachronic and equivalent soil mass approach. The three experiments were established in 2009 in a randomized complete block design with triplicates comprising maize (MaiEx)-, soybean (SoyEx)-, and cassava (CasEx)-based experiments. Soil samples were collected in 2021, 10 years after the first sampling (2011), at 7 depths: 0–5, 5–10, 10–20, 20–40, 40–60, 60–80, and 80–100 cm. Over 10 years, NTs altered SOC stock and its vertical distribution. SOC stock in NT systems noticeably increased between 6.5 and 14.7 Mg C ha-1 at 0–100 cm across the three experiments, with significant increase in 0–10, 0–20, and 0–40 cm depth under SoyEx, MaiEx and CasEx, respectively. The average SOC accumulation rate in the whole profile under NTs ranged from 0.86–1.47, 0.65–1.00, and 0.70–1.07 Mg C ha-1 yr-1 under MaiEx, SoyEx, and CasEx, respectively. In contrast, N stock in NT soils only increased in 0–5 cm but decreased below 5 cm in all three experiments. The average N stock loss in the NT soils ranged between -0.06 and -0.11 Mg N ha-1 yr-1 in 0–100 cm in all three experiments. In 0–10 cm, NT systems significantly increased particulate organic C (POM-C) by 115% and 118% in MaiEx and SoyEx, respectively, and by 37% in CasEx although this was insignificant. Similarly, NT systems enhanced C in the mineral-associated organic C (MAOC) fraction by 33% and 21% in 0–10 cm in MaiEx and SoyEx and even deeper to the soil profile > 60 cm in CasEx. Our findings suggest that long-term NT cropping systems with diverse crop species and a high amount of biomass-C inputs lead to SOC accumulation, including in the subsoil. This study highlights the potential of NT systems in sequestering and stabilizing SOC over time but raises questions about soil N dynamics.

Mots-clés libres : No-tillage, Conservation agriculture, Soil organic carbon, Climate change mitigation, Agroecology, Cover crops

Auteurs et affiliations

• Leng Vira, CIRAD-PERSYST-UPR AIDA (FRA)
• Cardinael Rémi, CIRAD-PERSYST-UPR AIDA (ZWE) ORCID: 0000-0002-9924-3269
• Tivet Florent, CIRAD-PERSYST-UPR AIDA (KHM)
• Seng Vang, Ministry of Agriculture, Forestry and Fisheries (Cambodge) (KHM)
• Mark Phearum, Ministry of Agriculture, Forestry and Fisheries (Cambodge) (KHM)
• Lienhard Pascal, CIRAD-PERSYST-UPR AIDA (VNM)
• Filloux Titouan, CIRAD-PERSYST-UPR AIDA (KHM)
• Six Johan, ETH (CHE)
• Hok Lyda, Royal University of Agriculture (KHM)
• Boulakia Stéphane, CIRAD-PERSYST-UPR AIDA (FRA) ORCID: 0000-0003-4331-1207
• Briedis Clever, UFV (BRA)
• De Moraes Sa Joao Carlos, UEPG (BRA)
• Thuries Laurent, CIRAD-PERSYST-UPR Recyclage et risque (FRA) ORCID: 0000-0002-1365-7891

Source : Cirad-Agritrop (https://agritrop.cirad.fr/609494/)

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