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Initial soil organic carbon concentration influences the short-term retention of crop-residue carbon in the fine fraction of a heavy clay soil |
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| Authors: | Vincent Poirier Denis A Angers Philippe Rochette Joann K Whalen |
| Institution: | 1. Soils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, 2560 Hochelaga Blvd., Québec, Québec, Canada, G1V 2J3 2. Department of Natural Resource Sciences, Macdonald Campus of McGill University, 21111 Lakeshore Road, Ste. Anne de Bellevue, Québec, Canada, H9X 3V9 3. Département des sciences du bois et de la forêt, Université Laval, 2405 de la Terrasse, Québec, Québec, Canada, G1V 0A6 |
| Abstract: | Among factors controlling decomposition and retention of residue C in soil, effect of initial soil organic C (SOC) concentration remains unclear. We evaluated, under controlled conditions, short-term retention of corn residue C and total soil CO2 production in C-rich topsoil and C-poor subsoil samples of heavy clay. Topsoil (0–20 cm deep, 31.3 g SOC kg?1 soil) and subsoil (30–70 cm deep, 4.5 g SOC kg?1 soil) were mixed separately with 13C–15N-labeled corn (Zea mays L.) residue at rates of 0 to 40 g residue C kg?1 soil and incubated for 51 days. We measured soil CO2–C production and the retention of residue C in the whole soil and the fine particle-size fraction (<50 μm). Cumulative C mineralization was always greater in topsoil than subsoil. Whole-soil residue C retention was similar in topsoil and subsoil at rates up to 20 g residue C kg?1. There was more residue C retained in the fine fraction of topsoil than subsoil at low residue input levels (2.5 and 5 g residue C kg?1), but the trend was reversed with high residue inputs (20 and 40 g residue C kg?1). Initial SOC concentration affected residue C retention in the fine fraction but not in the whole soil. At low residue input levels, greater microbial activity in topsoil resulted in greater residue fragmentation and more residue C retained in the fine fraction, compared to the subsoil. At high residue input levels, less residue C accumulated in the fine fraction of topsoil than subsoil likely due to greater C saturation in the topsoil. We conclude that SOC-poor soils receiving high C inputs have greater potential to accumulate C in stable forms than SOC-rich soils. |
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