Perennial crop growth in oil-contaminated soil in a boreal climate Lijuan Yan a, ⁎, Petri Penttinen a , Asko Simojoki b , Frederick L. Stoddard c , Kristina Lindström a a Department of Environmental Sciences, PO Box 65 (Viikinkaari 2a), 00014 University of Helsinki, Helsinki, Finland b Department of Food and Environmental Sciences, PO Box 27 (Latokartanonkaari 11), 00014 University of Helsinki, Helsinki, Finland c Department of Agricultural Sciences, PO Box 27 (Latokartanonkaari 5), 00014 University of Helsinki, Helsinki, Finland HIGHLIGHTS • Fodder galega and smooth brome were grown in motor oil contaminated soil. • 40 months after the oil spike 8%–27% of the oil remained in soil. • Oil degradation followed first-order kinetics and was fastest in bare fallow. • Oil increased crop dry matter and nitrogen yield. • Inoculated fodder galega could fully replace nitrogen fertilizer for brome grass. GRAPHICAL ABSTRACT abstract article info Article history: Received 26 January 2015 Received in revised form 22 May 2015 Accepted 12 June 2015 Available online xxxx Editor: D. Barcelo Keywords: Phytoremediation Oil degradation Fodder galega Crop growth Biological nitrogen fixation Soil contamination by petroleum hydrocarbons is a global problem. Phytoremediation by plants and their asso- ciated microorganisms is a cost-effective strategy to degrade soil contaminants. In boreal regions the cool climate limits the efficiency of phytoremediation. The planting of oil-tolerant perennial crops, especially legumes, in oil- contaminated soil holds promise for great economic benefits for bioenergy and bio-fertilizer production while ac- celerating the oil degradation process. We established a multi-year field experiment to study the ecological and agronomic feasibility of phytoremediation by a legume (fodder galega) and a grass (smooth brome) in a boreal climate. In 40 months, soil oil content decreased by 73%–92%, depending on the crop type. The oil degradation followed first-order kinetics with the reduction rates decreasing as follows: bare fallow N galega–brome grass mixture N brome grass N galega. Surprisingly, the presence of oil enhanced crop dry matter and nitrogen yield, particularly in the fourth year. The unfertilized galega–brome grass mixture out-yielded the N-fertilized pure grass swards over years by an average of 33%. Thus, a perennial legume–grass mixture is both ecologically and agronomically sustainable as a cropping system to alleviate soil contamination in the boreal zone, with consider- able potential for bioenergy and bio-fertilizer production. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Soil pollution by petroleum hydrocarbons (PHCs) is an increasing problem around the world. In Finland, for example, the number of contaminated sites grew from 10,400 in 1994 to 23,850 in 2013 (Pyy et al., 2013). In situ bioremediation using indigenous microbes is an ef- fective and low-cost strategy to degrade contaminants, but this process is limited by microbial activities, the biochemistry of enzymes, the Science of the Total Environment 532 (2015) 752–761 ⁎ Corresponding author. E-mail address: lijuan.yan@helsinki.fi (L. Yan). http://dx.doi.org/10.1016/j.scitotenv.2015.06.052 0048-9697/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv