Carbon sequestration in Mediterranean soils following afforestation of abandoned crops: Biases due to changes in soil compaction and carbonate stocks

Abstract

Crop replacement by secondary forests increases soil organic carbon (OC) stocks.Quantifying this increase is subject to biases: the changes in soil compaction and, in calcareous zones, the changes in soil inorganic carbon (IC) content, which affect the carbon balance. How relevant are both biases, though? We studied this problem in NE Spain, subhumid Mediterranean, in a set of current crops, old forests, and new forests grown on croplands abandoned after 1956. We compared soil OC stocks on a fixed-depth basis (30 cm), and on an equivalent-mass basis: uppermost 425 kg m À2 of fine mineral matter (amount in crop soils). Down to 30 cm, OC stocks were lowest in crops (5.45 kg m À2 ) and highest in old forests (7.50 kg m À2 ), which gives a potential OC sequestration in the mineral soil of 2.05 kg m À2 . On an equivalent-mass basis, the potential is 2.50 kg m À2 , meaning that the fixed-depth criterion underestimates OC sequestration by more than 20%. These figures are surpassed by those of IC: crops store 17.73 kg IC m À2 down to 30 cm, old forests 12.28, suggesting a potential loss upon afforestation of 5.45 kg IC m À2 . Nevertheless, the lack of negative relationships between IC losses and OC gains within a given land use suggests that the contrasting IC stocks result from past management, mainly tillage. The decarbonation is only apparent. Our results stress the need of accounting for changes in carbonate content and soil compaction in future studies about carbon sequestration in soils.

Soil carbon sequestration potential of planting hedgerows in agricultural landscapes

“…This supports the body of literature highlighting the importance of applying the ESM correction method when estimating SOC across different land use types ( Murphy et al, 2004 ; VandenBygaart and Kay, 2004 ; Vero et al, 2014 ) instead of the traditional ESV methods used in most publications ( Ellert and Bettany, 1995 ; VandenBygaart, 2006 ; Wendt and Hauser, 2013 ). The FD method has been shown to introduce bias when soil bulk density differs among treatments or has changed over time because of land use change ( Lee et al, 2009 ; Schrumpf et al, 2011 ; Wendt and Hauser, 2013 ; Rovira et al, 2015 ; Juvinyà et al, 2021 ). SOC ESM corrections have recently been advised as standard protocol by the Intergovernmental Panel on Climate Change ( Ogle et al, 2019 ), thus, from this point on our discussion focuses on the SOC ESM stocks presented in the results section.…”

Sequestering Organic Carbon in Soils Through Land Use Change and Agricultural Practices: A Review

“…North-east Spain Agriculture to orchards 60 30 0.42 [36] Humid continental Czech Agriculture to mixed species 14 20 -0.01 to 0.95 [37] Reforestation…”