Work

Legacy of severe soil degradation hinders the buildup of mineral-associated soil organic carbon

Year: 2025

Type: article

Abstract: Global efforts target a soil organic carbon (SOC) enhancement rate of 2.4 ‰ y −1 in the upper 30 cm of agricultural soils to address declining soil productivity associated with declining SOC stocks. We explored a unique chronosequence of homogeneous soils formed after mining in Germany, which serve conventional agriculture and exhibit a large margin for SOC storage, but limited SOC accrual, to study SOC protection mechanisms and accrual constraints. We hypothesized that limited SOC accrual is associated to insufficient nitrogen rather than to minerals saturation. Soil samples (0–30 and 30–60 cm) were collected across the chronosequence (0–56 years) and compared to an original non-mined soil (OS) managed similarly. The mean residence time (MRT) of SOC and its protection mechanisms were studied using soil incubation, organic matter density fractionation, and δ 13 C measurements. After 56 years, total and mineral-associated SOC (MAOC) stocks remained 18 % and 28 % lower than in the OS at 0–30 cm, with estimated replenishment times of 93 and 129 years, respectively. Mineral-associated nitrogen (MAN) stocks stagnated along recultivation time below OS level. Together with significant linear correlation of MAOC with total SOC and MAN stocks, these results indicate that nitrogen rather than saturation of minerals limits SOC accrual. In fact, the MAOC stock deficit to saturation was estimated at 316.4 Mg ha −1 . At 30–60 cm, SOC and nitrogen stocks were restored within 30 years, due to comparatively lower initial losses. The initial MRT of SOC at 0–30 and 30–60 cm (15.3 and 27.9 years) declined before finally becoming comparable to OS (11.7 and 7.7 years). This reflected new carbon entering the soil that initially contained predominantly MAOC (78–82 %), followed by its stabilization as MAOC. Due to their susceptibility to nitrogen losses, degraded soils require tailored nitrogen management to restore SOC stocks and comply with European laws requiring agricultural SOC accrual. Re -implementation of conventional agriculture together with the legacy of soil degradation hinder the accrual of mineral-associated soil organic carbon (MAOC). Steadying of mineral-associated nitrogen (MAN) indicates that the accrual of MAOC deriving from microbial activity requiring N is limited under these circumstances. The mean residence time (MRT) of soil organic carbon (SOC) initially decreases in response to new carbon entering the soil and thereafter increases with its stabilization as MAOC. • 56-year conventional agriculture chronosequence unravelling SOC accrual constraints. • 93 and 129 years are estimated to replenish total and mineral-associated SOC stocks. • MAN stocks stagnation indicates N-deficit for microbial-derived C stabilization. • MAOC accrual limited by N and system, rather than by minerals C-saturation. • Optimization of C and mainly N needed to achieve higher MAOC and SOC steady-states.

Source: The Science of The Total Environment

DOI: 10.1016/j.scitotenv.2025.179445

Authors: Otávio dos Anjos Leal, Rüdiger Reichel, Holger Wissel, Nicolas Brüggemann

Institution: Forschungszentrum Jülich

Language: English

Topic: Soil Carbon and Nitrogen Dynamics

Subfield: Soil Science

Field: Agricultural and Biological Sciences

Domain: Life Sciences

SDGs: Life on land, Zero hunger, Climate action

Open Access status: hybrid

Estimated APC paid: $4,250