Work

Soil Organic Carbon and Nitrogen Stocks and Isotopic Signatures Under Contrasting Integrated Crop‐Livestock Systems in Sub‐Humid Zimbabwe

Year: 2026

Type: article

Abstract: ABSTRACT Soil organic carbon (SOC) and soil total nitrogen (STN) are critical indicators of soil health and vital sinks in agroecosystems. However, knowledge gaps remain regarding how long‐term crop‐livestock integration impacts coupled SOC and STN stocks on commercial versus communal smallholder farms in Africa. This study quantified whole profile SOC and STN stocks under two land‐use types (croplands and grazing lands) and two livestock management facilities (congregation points and corrals), across two adjacent, distinct mixed crop‐livestock farming systems, while evaluating how these land uses influence δ 13 C and δ 15 N isotopic signatures. A commercial farm and an adjacent communal smallholder farm with similar soil types were selected. Soil samples were collected from six depth increments (0–5, 5–10, 10–20, 20–40, 40–70, 70–100 cm) to determine profile‐wide SOC and STN stocks alongside their δ 13 C and δ 15 N signatures. Land‐use and management type impacted SOC and STN stocks more significantly in the communal system ( p < 0.001) than on the commercial farm ( p < 0.05). On the commercial farm, whole‐profile SOC (Mg C ha −1 ± SE) and STN (Mg N ha −1 ± SE) stocks peaked in grazing lands (129.7 ± 12.8; 10.32 ± 1.14) and reached minimums at livestock congregation points (68.1 ± 2.7; 7.04 ± 1.16). Conversely, in the communal smallholder system, both stocks peaked sharply at livestock congregation points (150.0 ± 4.6; 12.26 ± 0.27) and were lowest in croplands (56.5 ± 1.5; 5.20 ± 0.20). Deep subsoil layers (40–100 cm) stored a greater relative proportion of total stocks on the commercial farm (36%–43% SOC; 39%–45% STN) than on the smallholder farm (28%–39% SOC; 29%–39% STN). Soil δ 15 N values increased with depth across all land‐use and management types. Lower δ 15 N values in commercial croplands compared with smallholder croplands likely reflect higher synthetic fertilizer use, while the highest δ 15 N values occurred in cattle corrals. Contrary to typical microbial fractionation—where preferential loss of 12 C during respiration enriches δ 13 C at depth—no consistent vertical increase in δ 13 C was observed; all land‐use types were enriched, averaging −17‰. Our results demonstrate that, within the narrow range of soil textures evaluated, land‐use and management serve as the primary determinants of SOC and STN stocks and their isotopic signatures. While livestock congregation points create intense, localized nutrient hotspots, their small spatial extent limits their landscape‐scale sequestration. Consequently, adopting conservation practices in commercial croplands as a proactive intervention, and optimizing the management of extensive communal grazing lands and croplands are collectively essential for enhancing regional biogeochemical storage and ecosystem resilience.

Source: Soil Use and Management

DOI: 10.1111/sum.70315