Europ. J. Agronomy 66 (2015) 62–73 Contents lists available at ScienceDirect European Journal of Agronomy j ourna l ho me page: www.elsevier.com/locate/eja Do soil organic carbon levels affect potential yields and nitrogen use efﬁciency? An analysis of winter wheat and spring barley ﬁeld trials Myles Oelofse a,∗ , Bo Markussen b , Leif Knudsen c , Kirsten Schelde d , Jørgen E. Olesen d , Lars Stoumann Jensen a , Sander Bruun a a Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, Thorvaldsensvej 40, 1871 Frederiksberg, Denmark b Laboratory of Applied Statistics, Department of Mathematical Sciences, Faculty of Science, University of Copenhagen, Universitetsparken 5, 2100 Copenhagen Ø, Denmark c SEGES, Agro Food Park 15, 8200 Aarhus N, Denmark d Department of Agroecology, Aarhus University, Blichers Allé 20, P.O. Box 50, 8830 Tjele, Denmark a r t i c l e i n f o Article history: Received 29 April 2014 Received in revised form 23 February 2015 Accepted 23 February 2015 Keywords: Soil organic carbon Soil organic matter Wheat Barley Crop productivity Nitrogen use efﬁciency a b s t r a c t Soil organic carbon (SOC) is broadly recognised as an important parameter affecting soil quality, and can therefore contribute to improving a number of soil properties that inﬂuence crop yield. Previous research generally indicates that soil organic carbon has positive effects on crop yields, but in many studies it is difﬁcult to separate the effect of nutrients from the effect of SOC in itself. The aim of this study was to analyze whether the SOC content, in itself, has a signiﬁcant effect on potential yields of commonly grown cereals across a wider range of soil types in Denmark. The study draws on historical data sets from the Danish national ﬁeld trials consisting of 560 winter wheat (Triticum aestivum L.) trials and 309 spring barley (Hordeum vulgare L.) trials conducted over the past 20 and 17 years, respectively. We hypothesised that for these two crops, the potential grain yield, the yield with no fertiliser N application and the N use efﬁciency would be positively affected by SOC level. A statistical model was developed to explore relationships between SOC and potential yield, yields at zero N application and N use efﬁciency (NUE). The model included a variety of variables and aimed to elucidate the sole effect of SOC by controlling for potential confounding variables. No signiﬁcant effect of SOC on potential winter wheat was found, whilst for spring barley, only for the course sandy loam soil type was a borderline signiﬁcantly positive effect of SOC on potential yields found. The relationship between unfertilized plot yields and SOC was positive for winter wheat, although not signiﬁcant, whilst for spring barley a signiﬁcant positive effect of SOC was found only for the coarse sandy soil type, and a borderline signiﬁcant positive effect of SOC was found for the coarse sandy loam soil type. A signiﬁcant negative relationship was found between SOC and NUE for both winter wheat and spring barley. Based on the large dataset analyzed, we cautiously challenge the importance of SOC in contributing to crop productivity in contexts with similar soils and climate, and we speculate that in situations where nutrient limitation does not occur, SOC levels above 1% may be sufﬁcient to sustain yields. In light of the ﬁndings presented in this study, further work should be conducted which can further elucidate the effect of SOC on yields. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Soil organic matter (SOM) is broadly recognised as an impor- tant parameter affecting soil quality (Diacono and Montemurro, 2010; Johnston et al., 2009). Therefore, land use and management systems which maintain or enhance levels of SOM are considered pivotal in ensuring agricultural sustainability and productivity (Lal, 2006). SOM is furthermore of global environmental importance ∗ Corresponding author. Tel.: +45 35 33 34 42; fax: +45 35 33 34 60. E-mail address: myles@plen.ku.dk (M. Oelofse). primarily due to the role that soil organic carbon 1 (SOC) plays in carbon sequestration (Morgan et al., 2010). Crop yields are inﬂuenced by a range of factors including solar radiation, water and nutrient availability and pest and weed pres- sure (Evans, 1993). Soil organic matter inﬂuences soil biological, physical and chemical properties, therefore from an agronomic perspective, SOM is considered important as it can contribute in a variety of ways to improving some of the factors inﬂuencing 1 We use the terms SOM and SOC interchangeably. In our analysis, we refer pri- marily to SOC, whilst in Sections 1 and 4 we use both terms according to how cited references have used the term. http://dx.doi.org/10.1016/j.eja.2015.02.009 1161-0301/© 2015 Elsevier B.V. All rights reserved.