Enhancing Soil Organic Matter as a Route to the Ecological Intensification of European Arable Systems

Ecosystems https://doi.org/10.1007/s10021-018-0228-2 Ó 2018 The Author(s). This article is an open access publication Enhancing Soil Organic Matter as a Route to the Ecological Intensification of European Arable Systems M. P. D. Garratt,1* R. Bommarco,2 D. Kleijn,3 E. Martin,4 S. R. Mortimer,1 S. Redlich,4 D. Senapathi,1 I. Steffan-Dewenter,4 S. Świtek,5 V. Takács,5 S. van Gils,6 W. H. van der Putten,7 and S. G. Potts1 1 Centre for Agri-Environmental Research, School of Agriculture, Policy and Development, University of Reading, Reading RG6 6AR, UK; 2Department of Ecology, Swedish University of Agricultural Sciences, Uppsala, Sweden; 3Plant Ecology and Nature Conservation Group, Wageningen University and Research, Wageningen, The Netherlands; 4Department of Animal Ecology and Tropical Biology, Biocenter, University of Würzburg, Würzburg, Germany; 5Institute of Zoology, Poznań University of Life Sciences, Poznań, Poland; 6 Department of Terrestrial Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands; 7Laboratory of Nematology, Wageningen University and Research (WUR), P.O. Box 8123, 6700 ES Wageningen, The Netherlands ABSTRACT Soil organic matter (SOM) is declining in most agricultural ecosystems, impacting multiple ecosystem services including erosion and flood prevention, climate and greenhouse gas regulation as well as other services that underpin crop production, such as nutrient cycling and pest control. Ecological intensification aims to enhance crop productivity by including regulating and supporting ecosystem service management into agricultural practices. We investigate the potential for increased SOM to support the ecological intensification of arable systems by reducing the need for Received 1 July 2017; accepted 21 January 2018 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-018-0228-2) contains supplementary material, which is available to authorized users. Author Contributions MPDG, RB, DK, EM, SM, SR, ISD, SS, VT, SvG and SP conceived the ideas and designed the methodology; MPDG, RB, DS, SR, SS, VT and SvG collected the data; MPDG analysed the data; MPDG, RB, DK, EM, SM, SR, DS, SS, ISD, VT, WHvdP, SvG and SP contributed significantly to writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication. Data Accessibility Data are available through the University of Reading ‘Research data archive’ at https://doi.org/10.17864/1947.136 *Corresponding author; e-mail: nitrogen fertiliser application and pest control. Using a large-scale European field trial implemented across 84 fields in 5 countries, we tested whether increased SOM (using soil organic carbon as a proxy) helps recover yield in the absence of conventional nitrogen fertiliser and whether this also supports crops less favourable to key aphid pests. Greater SOM increased yield by 10%, but did not offset nitrogen fertiliser application entirely, which improved yield by 30%. Crop pest responses depended on species: Metopolophium dirhodum were more abundant in fertilised plots with high crop biomass, and although population growth rates of Sitobion avenae were enhanced by nitrogen fertiliser application in a cage trial, field populations were not affected. We conclude that under increased SOM and reduced fertiliser application, pest pressure can be reduced, while partially compensating for yield deficits linked to fertiliser reduction. If the benefits of reduced fertiliser application and increased SOM are considered in a wider environmental context, then a yield cost may become acceptable. Maintaining or increasing SOM is critical for achieving ecological intensification of European cereal production. M. P. D. Garratt and others Key words: aphids; ecological intensification; fertiliser, soil organic matter; arable farming. INTRODUCTION Developing agricultural systems less dependent on unsustainable inputs, yet meeting the needs of a growing population, is a key challenge for food production systems in the future (Garnett and others 2013). Taking an ecosystem approach to agricultural food production is the goal of ecological intensification, which aims to enhance crop productivity by including regulating and supporting ecosystem service management into agricultural practices to reduce reliance on unsustainable inputs such as mineral fertiliser and pesticides (Bommarco and others 2013). A number of these ecosystem services including pollination by insects and crop pest regulation by natural enemies are supported by natural habitats located in the agricultural landscape, and it is at this scale that they need to be protected and managed to promote ecological intensification (Tscharntke and others 2005; Power 2010). Additionally, management at the field scale is key to effective ecological intensification. For example, soil organic matter decline, and the loss of the functionally important soil organisms it supports, is a major threat to the sustainability of agricultural systems (Gardi and others 2013; Tsiafouli and others 2015). Soil biodiversity loss can compromise key processes that deliver ecosystem goods and services on which effective ecological intensification relies, including decomposition and nutrient cycling (Lavelle and others 2006; Barrios 2007). Ecologically intensive practices include increased crop diversification, legumes in a rotation, application of organic fertilisers and minimising soil disturbance (Drinkwater and others 1998; Edmeades 2003; Kremen and Miles 2012). These may increase soil organic matter (SOM) and the biodiversity-based belowground ecosystem services it supports to enhance sustainability of agricultural systems and maintain or improve crop yields (Lal 2006; Barrios 2007; Brady and others 2015). Not only does retaining high soil organic matter affect nutrient availability and growth of crop plants, but soils can also have direct or indirect resource-based (bottom-up) effects on crop pests through a variety of mechanisms. High organic matter content in soil can support a greater diversity of soil organisms, which provide alternative food sources for natural enemies that help to sup- press crop pests (Scheu 2001; Birkhofer and others 2008). In addition, the ‘mineral balance hypothesis’ proposed by Phelan and others (1996) states that the balance of nutrients often found in organically managed soils promotes optimum conditions for plant growth, prevents pulses of available nutrients in plant tissues and reduces palatability or preference by pests (Altieri and Nicholls 2003; Alyokhin and others 2005). Accordingly, increases in soil organic matter may not only promote high soil organism abundance and diversity, but also lower pest pressure on crops. In conventional, intensive agriculture, crop pests generally benefit from the application of fertilisers (Garratt and others 2011; Butler and others 2012). One group of insect (...truncated)