Soil organic matter stability in forest and cropland components of two agroforestry systems in western Canada

Agroforestry systems play important roles in carbon (C) sequestration in western Canada. However, the effect of agroforestry system type and their component land-uses (forested area and cropland) on soil organic C (SOC) stability is poorly understood. We studied SOC stability in surface soils from two agroforestry systems (shelterbelt system and hedgerow system) and their component land-uses (forested area and cropland) in western Canada. A 61-day laboratory incubation was used to assess SOC biological stability, and compared to thermal stability measured during ramped combustion. The shelterbelt system had a lower biological stability than the hedgerow system as indicated by the higher cumulative soil respiration and SOC loss during incubation. Cumulative respiration and SOC loss during incubation in the forested area was 1.63 and 1.57 times that in the cropland, indicating a lower SOC biological stability in the former. Thermal stability indicators, CO2-T50 (the temperature at which half of the CO2 is produced), DSC-T50 (the temperature at which half of the exothermic energy of the SOC is released) and ROI (return on energy investment) were influenced by the interactive effects of the agroforestry system by land-use, while TG-T50 (the temperature at which half of the exothermic mass is lost) and Ed (energy density) were influenced by land-use and the interactive effects of agroforestry system by land-use. Hedgerow cropland had a higher SOC thermal stability (higher TG-T50) than the hedgerow forested area, while there was no difference among shelterbelt cropland, and the forested areas of shelterbelt and hedgerow system. We conclude that planting trees on agricultural land to form agroforestry systems alters SOC biological and thermal stabilities, and the hedgerow system may have a more stable SOC than the shelterbelt system, thus, maintaining the hedgerow system may enhance C stability, promote C sequestration and climate change mitigation.

Automated summary

Agroforestry systems in western Canada play important roles in carbon sequestration, but the impact of system type and component land-uses on soil organic carbon (SOC) stability is poorly understood. This study investigated SOC stability in two agroforestry systems (shelterbelt and hedgerow) and their component land-uses (forested area and cropland) using a 61-day laboratory incubation and thermal stability measurements. The results showed that the shelterbelt system had lower biological stability than the hedgerow system, with higher soil respiration and SOC loss during incubation. Thermal stability indicators were influenced by interactive effects of agroforestry system by land-use, and land-use alone. The hedgerow cropland had higher SOC thermal stability than the hedgerow forested area. The findings suggest that planting trees in agricultural land to form agroforestry systems can alter SOC stability, and the hedgerow system may enhance C stability, promote C sequestration, and climate change mitigation.