Changes in particulate and mineral-associated organic carbon with land use in contrasting soils
Section snippets
INTRODUCTION
Globally, organic carbon (OC) content in the top 0−100 cm soil has been estimated to be in the range of 3 500−4 800 Pg carbon (C) (Lehmann and Kleber, 2015), with nearly a quarter of this amount present in the upper 20 cm of soil (Jobbágy and Jackson, 2000; Guo and Gifford, 2002). The soil OC (SOC) pool is much greater than other terrestrial OC pools, e.g., vegetation (420−620 Pg C) and the atmosphere (829 Pg C) (Lehmann and Kleber, 2015). Thus, soils are viewed as a major reservoir and a
Site details
Four sampling locations were selected in New South Wales, Australia, with each location representing a distinct soil type: Ferralsol, Luvisol, Vertisol, and Solonetz. Soil was sampled from paired sites (native and cropped) at each location to investigate the effect of land use conversion on SOC dynamics. The paired sites at each location were directly adjacent and represented similar landscapes, positions, climatic conditions, and major soil characteristics. For each of the four soil types, the
General soil properties
Soils from the paired sites (native and cropped) at both depths were non-saline (EC: 0.09−0.75 dS m−1) and acidic in reaction (pH ≤ 6.8) except for the subsurface soils of the Vertisol, which were slightly alkaline (pH: 7.7−7.8) (Table I). The CEC of each soil did not vary under different land uses but increased with depth for the Luvisol, Vertisol (native), and Solonetz and decreased slightly with depth in the Ferralsol. In general, the Vertisol showed the highest CEC (200−231 mmolc kg−1),
General trends of OC and N
Narrower C:N ratio and larger δ13C and δ15N values of the MOM fractions in contrast to the POM fractions in all soils (Table III) suggest a more advanced phase of OM decomposition in the MOM fractions (Baldock et al., 1992; John et al., 2005). Generally, the C:N ratio in soils decreases with depth (Rumpel and Kögel-Knabner, 2011), which is ascribed to more microbially processed OC (Boström et al., 2007). The C:N ratio of MOM fractions of the subsurface soils in this study also showed an overall
CONCLUSIONS
Land use change (native to cropped) impacted the OC in both surface and subsurface soils. The MOM fractions were not necessarily resistant to land use conversion, particularly in surface soils. Isotopic compositions (δ13C, δ15N, and 14C content) highlighted the effect of vegetation on changes in OC via fresh OM supply to surface soils. Under different OC loading conditions in surface soils, POM was less sensitive because of the continuous input of agricultural crop residues. Among the MOM
ACKNOWLEDGEMENTS
We acknowledge Dr. Claudia Keitel of Centre for Carbon, Water and Food, The University of Sydney, New South Wales, Australia for technical and analytical support in mass spectroscopic analysis. The corresponding author acknowledges the financial support of the International Postgraduate Research Scholarships and Postgraduate Research Support Scheme of the University of Sydney. The authors express gratitude to the Australian Institute of Nuclear Science and Engineering for providing a research
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2023, GeodermaCitation Excerpt :POC is formed from fresh or partly decomposed plant materials, often referred to as labile organic C, which are rapidly decomposable (Zimmermann et al., 2007). Thus, POC has a relatively shorter turnover time, and is considered as being more sensitive to management than mineral associated organic C (YEASMIN et al., 2022). As in our study, the literature has previously shown that POC usually increases under reduced tillage and when crop residues are returned to the soil (BEGUM et al., 2022; Jin et al., 2021; Samson et al., 2020).