Agriculture, Ecosystems and Environment 140 (2011) 218–225 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee Soil C storage as affected by tillage and straw management: An assessment using field measurements and model predictions Kees Jan van Groenigen a,b,∗ , Astley Hastings c , Dermot Forristal d , Brendan Roth a , Mike Jones a , Pete Smith c a Department of Botany, School of Natural Science, Trinity College Dublin, Dublin 2, Ireland b Department of Biological Sciences and Merriam-Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ 86011, USA c Institute of Biological and Environmental Sciences, School of Biological Sciences, University of Aberdeen, 23 St Machar Drive, Aberdeen AB24 3UU, UK d Teagasc Crops Research Centre, Oak Park, Carlow, Ireland article info Article history: Received 27 August 2010 Received in revised form 3 December 2010 Accepted 6 December 2010 Available online 11 January 2011 Keywords: Tillage Soil C storage Straw management Soil C modelling abstract Soil tillage and straw management are both known to affect soil organic matter dynamics. However, it is still unclear whether, or how, these two practices interact to affect soil C storage, and data from long term studies are scarce. Soil C models may help to overcome some of these problems. Here we compare direct measurements of soil C contents from a 9 year old tillage experiment to predictions made by RothC and a cohort model. Soil samples were collected from plots in an Irish winter wheat field that were exposed to either conventional (CT) or shallow non-inversion tillage (RT). Crop residue was removed from half of the RT and CT plots after harvest, allowing us to test for interactive effects between tillage practices and straw management. Within the 0–30 cm layer, soil C contents were significantly increased both by straw retention and by RT. Tillage and straw management did not interact to determine the total amount of soil C in this layer. The highest average soil C contents (68.9 ± 2.8 Mg C ha -1 ) were found for the combination of RT with straw incorporation, whereas the lowest average soil C contents (57.3 ± 2.3 Mg C ha -1 ) were found for CT with straw removal. We found no significant treatment effects on soil C contents at lower depths. Both models suggest that at our site, RT stimulates soil C storage largely by decreasing the decomposition of old soil C. Extrapolating our findings to the rest of Ireland, we estimate that RT will lead to C mitigation ranging from 0.18 to 1.0 Mg C ha -1 y -1 relative to CT, with the mitigation rate depending on the initial SOC level. However, on-farm assessments are still needed to determine whether RT management practices can be adopted under Irish conditions without detrimental effects on crop yield. © 2010 Elsevier B.V. All rights reserved. 1. Introduction During the last two centuries, arable farming has led to a world- wide decline in soil organic C (SOC) stocks (Lal, 2004). Several mechanisms have been shown to contribute to this trend. Firstly, soil disturbance during cultivation decreases the physical protec- tion of soil C against microbial decomposition (e.g. Six et al., 2000). Moreover, arable land is managed to maintain close to neutral pH levels and drained to avoid water logging, thereby further stimu- lating microbial oxidation of SOC. Finally, arable soils with annual crops are typically covered with vegetation for a relatively short time compared to natural ecosystems, causing lower soil C input rates (Baker et al., 2007). Besides its negative effect on soil quality, ∗ Corresponding author at: Department of Biological Sciences and Merriam- Powell Center for Environmental Research, Northern Arizona University, Flagstaff, AZ 86011, USA. Tel.: +1 928 523 5897. E-mail address: cjvangroenigen@nau.edu (K.J. van Groenigen). a loss of soil C also adds to anthropogenic CO 2 emissions (Lal, 2007; Sauerbeck, 2001). These issues spurred research interest in man- agement practices that may arrest or partly reverse C losses from arable lands (Post and Kwon, 2000; Smith et al., 1998, 2000). Most notably, reduced tillage (RT) and straw management have been suggested as instruments for soil C storage (Jarecki and Lal, 2003); whereas RT minimizes soil disturbance, the retention of crop residue increases soil C input. Although straw retention and RT practices have both been reported to improve soil quality (e.g. Salinas-Garcia et al., 1997; Mann et al., 2002; van Groenigen et al., 2010), claims of soil C storage are still widely debated. On the one hand, several studies have found that no-till (NT) and RT practices increase soil C contents in the top soil (West and Post, 2002; Smith et al., 1998; Ogle et al., 2005). However, other studies have sug- gested that C accumulation near the soil surface due to NT and RT practices might be negated by a loss of C at lower depths (e.g. Baker et al., 2007; Blanco-Canqui and Lal, 2008). It may take several decades before a new SOC equilibrium is reached following a change in management practices (Odell 0167-8809/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.agee.2010.12.008