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Dynamics of Soil Carbon Concentrations and Quality Induced by Agricultural Land Use in Central South Africa
Author(s) -
Loke P. F.,
Kotzé E.,
Preez C. C.,
Twigge L.
Publication year - 2019
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2018.11.0423
Subject(s) - soil carbon , soil water , environmental science , ecosystem , soil quality , agronomy , grassland , soil organic matter , chemistry , soil science , ecology , biology
Core Ideas Converting grasslands to cropland deprives soils of C regardless of lability or recalcitrant nature. Reversion into secondary grasslands can reverse soil C losses in semiarid agro‐ecosystems. Secondary grassland management improves SOC quality to resemble primary grasslands. Relative losses and gains of soil C fractions are modulated by climatic and soil conditions. Prolonged soil cultivation has been identified as a major cause of land degradation and a threat to soil quality in drought‐prone environments. This study evaluated land use effects on soil carbon (C) fractions and organic C (SOC) quality across three semiarid agro‐ecosystems (Harrismith, Tweespruit, and Kroonstad) in central South Africa. Soil samples were collected from croplands, primary and secondary grasslands at the 0‐ to 200‐mm layer in each agro‐ecosystem and analyzed for various soil C fractions. The SOC structure was characterized with 13 C nuclear magnetic resonance (NMR) spectroscopy. All analyses were done on bulk soil samples. Conversion of primary grasslands into croplands decreased C fractions by 27 to 90% across the three agro‐ecosystems, with highest losses recorded in Harrismith and Tweespruit and lowest in Kroonstad, suggesting site‐specific conditions acted together with cultivation to effect C losses. The 13 C NMR spectra revealed a slight change in SOC structural composition when O‐alkyl C decreased with concomitant increase in aromatic and alkyl C due to cultivation, with differences in the range of 1 to 11%. O‐alkyl C remained almost the same in Harrismith, suggesting that lignin‐derived methoxy groups were probably more dominant than easily decomposable carbohydrates as opposed to O‐alkyl C in Tweespruit and Kroonstad. Meanwhile, reversion of cultivated soils into perennial pastures restored and even increased some soil C fractions (by 3–129%) to represent primary grasslands, especially in Kroonstad. Organic C decomposition was lower in the cultivated soils relative to virgin and restored soils. This underscores the importance of determining plant biomass composition because these unusual responses were probably related to vegetation differences. Overall, this study demonstrates the potential of secondary grassland management to rehabilitate degraded cultivated soils with implications for restoration of agro‐ecosystem functions and services.