Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsevier.com/locate/agee Trees increase soil organic carbon and nutrient availability in temperate agroforestry systems P. Pardon a,b,c, ⁎ , B. Reubens a , D. Reheul b , J. Mertens d , P. De Frenne b , T. Coussement e , P. Janssens e , K. Verheyen c a Flanders Research Institute for Agriculture, Fisheries and Food (ILVO), Burgemeester Van Gansberghelaan 109, 9820 Merelbeke, Belgium b Department of Plant Production, Ghent University, Coupure Links 653, 9000 Ghent, Belgium c Department of Forest and Water Management, Ghent University, Geraardsbergsesteenweg 267, 9090 Gontrode, Belgium d Department of Applied Biosciences, Ghent University, Valentin Vaerwyckweg 1, 9000 Ghent, Belgium e Soil Service of Belgium, Willem de Croylaan 48, 3001 Leuven, Belgium ARTICLE INFO Keywords: Alley cropping Soil organic carbon Soil fertility Temperate agroforestry Poplar ABSTRACT Agroforestry systems (AFS) have a large potential to deliver a wide range of ecosystem services (ES). In field and crop management, changes to factors such as regulatory ES delivery are rarely taken into account, in part due to the paucity of detailed quantification of how trees affect biophysical field characteristics. This is especially true for arable systems in temperate climates. We have therefore assessed the influence of rows of trees of varying size on the prevailing soil characteristics in arable AFS. Spatial variability of soil organic carbon, acidity and nutrient status (N, P, K, Ca, Mg and Na) of the plough layer were analysed on a set of 17 arable agroforestry fields comprising 6 young (< 5 years) alley cropping fields and 11 fields bordered by a row of trees of moderate to older age (15–47 years) in Belgium. Significantly higher soil organic carbon and soil nutrient concentrations of N, P, K, Mg and Na were observed in the vicinity of trees in field boundaries, most likely resulting from the input of tree litter and nutrient-enriched throughfall water (for K and Na). Observed increases were strongly related to the distance from the tree row, resulting in a gradual change in soil conditions up to at least 30 m into the field. No significant effects of distance from the tree rows on soil characteristics were found in the young alley cropping fields. These results highlight the potential of middle-aged to mature tree rows to increase soil organic carbon stocks and nutrient availability for the agricultural crop in AFS. 1. Introduction In temperate regions, interest in agroforestry has been growing for 20 years (Borremans et al., 2016; Gillespie et al., 2000; Jose et al., 2004; Nair, 2007) because it is considered as a sustainable agricultural practice that combines primary production with other ecosystem ser- vices (ES) (Torralba et al., 2016). In this paper an AFS is defined as a land use system in which trees are grown in combination with agri- cultural crops, and where both ecological and economic interactions occur between the tree and non-tree components of the system (Oelbermann et al., 2004; Young, 1989). The tree component can be located either inside the field (e.g. “alley cropping”), or on the field edges (e.g. “boundary planting”)(Nair et al., 2009; Young, 1989). Several authors have highlighted the potential beneficial effects of AFS such as carbon sequestration (Cardinael et al., 2015a; Montagnini and Nair, 2004), protection of (ground)water quality through reduction of nitrogen leaching (Allen et al., 2004; Jose, 2009), mitigation of soil erosion (Nair, 2007) and biodiversity conservation (Klaa et al., 2005). However, in large parts of temperate Europe, implementation of agro- forestry remains rather limited (Reisner et al., 2007; Rigueiro- Rodríguez et al., 2009). Besides uncertainties on the legislative and economic level (Borremans et al., 2016), this might result from a lack of actual quantification of the ES provided and the lack of knowledge on implications of AFS on field management (Graves et al., 2009; Tsonkova et al., 2014). Particularly in regions with oceanic and continental climatic con- ditions (as defined by Peel et al. (2007)), further research and quanti- fication is needed regarding the effect of tree presence on soil organic carbon (SOC) (Cardinael et al., 2015a; Jose, 2009; Peichl et al., 2006) and soil nutrient availability (Cardinael et al., 2015a; Jose, 2009; Jose et al., 2000). For various AFS in the (sub-)tropical regions, the occur- rence and magnitude of these effects on SOC (e.g. Albrecht and Kandji, 2003; Gupta et al., 2009) and soil nutrient content (e.g. Nair et al., 1999; Szott et al., 1991) have already been thoroughly studied, where http://dx.doi.org/10.1016/j.agee.2017.06.018 Received 26 January 2017; Received in revised form 7 June 2017; Accepted 11 June 2017 ⁎ Corresponding author at: Department of Forest and Water Management, Ghent University, Geraardsbergsesteenweg 267, 9090 Gontrode, Belgium. E-mail address: paul.pardon@ilvo.vlaanderen.be (P. Pardon). Agriculture, Ecosystems and Environment 247 (2017) 98–111 0167-8809/ © 2017 Elsevier B.V. All rights reserved. MARK