In the Mediterranean rainfed systems, perennial warm-season grasses are profitable crops for the production of herbage as forage or feedstock for bioenergy purposes. During summer, when the production of cool-season crops is scarce, warm-season grasses can improve the productivity and stability of forage cropping systems. In Italy, switchgrass (Panicum virgatum L.) can be cultivated for herbage production or as energy crop. The objective of this work was evaluating if relay intercropping with cool-season legumes could be suited to convert a mature stand of switchgrass from energy to dual, energy and forage, production, together with improving the productivity and the quality of the harvestable biomass. All these things considered, a field experiment was carried out in Central Italy, on mature stands of two switchgrass varieties, Alamo and Blackwell, overseeded with two legumes: sulla (Hedysarum coronarium L.) and crimson clover (Trifolium incarnatum L.). The intercropping system was compared with fertilized and un-fertilized pure switchgrass stands. After two years of study, data showed that the intercropping increased the total above ground biomass (AGB) productivity. In the second year, the increase in total AGB production for switchgrass mixtures compared with the pure stands was greater for sulla, a biennial legume, than crimson clover. Introduction Future cropping systems have to meet several goals simultaneously: i) improving productivity of croplands and grasslands in order to produce food for increasing world population (Lutz et al., 2001); ii) reducing global environmental impact; iii) enhancing land-use efficiency; iv) mitigating climate changes through the reduction of greenhouse gases (GHG) emissions; and v) setting up adaptation strategies to reduce the vulnerability of crops by a sustainable intensification (Campbell et al., 2014; Godfray and Garnett, 2014; Pretty and Bharucha, 2014; Wezel et al., 2014). Several authors reported that the introduction of perennial crops, through the conversion from croplands to grasslands, can contribute to increase the sustainability of agricultural production (Glover et al., 2010, 2012). In fact, perennial crops can provide several ecosystem services such as: i) maintaining soil fertility; ii) increasing the soil carbon stock potential compared to annual crops (Glover et al., 2010; Monti, 2012); iii) enhancing soil protection by all-year-round vegetation cover and contrasting soil erosion (Durán Zuazo and Rodríguez Pleguezuelo, 2008; Vallebona et al., 2016); iv) improving biodiversity in farmland and guaranteeing higher resilience of the agro-ecosystem (Peyraud et al., 2014). In the Mediterranean, perennial warm-season grasses are profitable crops for the production of herbage as forage or feedstock for bioenergy utilization (Monti et al., 2012). In addition, in summer dry period when the conventional production, as pasture or fodder, is poor, warm-season grasses can improve the productivity and the stability of Mediterranean forage cropping systems (Gherbin et al., 2007). Among perennial warm-season grasses, switchgrass (Panicum virgatum L.), a prairie species, native of North America and originally domesticated for pasture production, was recognized for its ability of accumulating large amount of biomass even under drought conditions (Monti et al., 2012). Starting from the 90s, owing its high yield potential, switchgrass has been introduced in Europe as promising crop for bioenergy sector (Parrish et al., 2005). In the last decade, several studies highlighted the suitability of both lowland and upland ecotypes to Mediterranean environments (Monti et al., 2008, 2012; Alexopoulou et al., 2015; Nassi o Di Nasso et al., 2015). Furthermore, the literature evidenced that: i) switchgrass productivity decreases after the third year of cultivation (Alexopoulou et al., 2015); ii) multi-harvest systems (more than one cut per year) negatively affect the plantation life span (Monti et al., 2008); iii) switchgrass yields are affected by nitrogen (N) fertilization (Nassi o Di Nasso et al., 2015). Concerning the response of this crop to N fertilization, Ashworth et al. (2015b) indicated that sustainable production levels (evaluated using an life cycle assessment approach) could be achieved with low N fertilization rate (67 kg ha–1), since higher amount of N decreases the efficiency of the Correspondence: Giorgio Ragaglini, Institute of Life Sciences, Sant’Anna School of Advanced Studies, Via Santa Cecilia 3, 56127,

中文翻译：

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在柳枝稷 (Panicum virgatum L.) 成熟林分上对两种冷季豆科植物 (Hedysarum coronarium L. 和 Trifolium incarnatum L.) 进行交割提高了生物量生产力

在地中海雨育系统中，多年生暖季牧草是生产草料作为生物能源用途的草料或原料的有利可图的作物。在夏季，当冷季作物产量稀少时，暖季牧草可以提高牧草种植系统的生产力和稳定性。在意大利，柳枝稷 (Panicum virgatum L.) 可种植用于牧草生产或作为能源作物。这项工作的目的是评估与冷季豆科植物间作是否适合将成熟的柳枝稷林从能源转化为双能、能源和草料生产，同时提高可收获生物质的生产力和质量。考虑到所有这些因素，在意大利中部的两个柳枝稷品种的成熟林分上进行了田间试验，阿拉莫和布莱克威尔，与两种豆类交割：苏拉 (Hedysarum coronarium L.) 和深红色三叶草 (Trifolium incarnatum L.)。间作系统与施肥和未施肥的纯柳枝稷林进行了比较。经过两年的研究，数据显示间作提高了总地上生物量 (AGB) 生产力。在第二年，与纯林分相比，柳枝稷混合物的总 AGB 产量增加幅度大于 sulla（一种两年生豆科植物），而不是深红色三叶草。引言 未来的种植系统必须同时满足几个目标： i) 提高农田和草地的生产力，以便为不断增加的世界人口生产粮食（Lutz 等，2001）；ii) 减少全球环境影响；iii) 提高土地利用效率；iv) 通过减少温室气体 (GHG) 排放来缓解气候变化；v) 制定适应战略，通过可持续集约化降低作物的脆弱性（Campbell 等，2014；Godfray 和 Garnett，2014；Pretty 和 Bharucha，2014；Wezel 等，2014）。几位作者报告说，通过从农田转变为草地，引入多年生作物有助于提高农业生产的可持续性（Glover 等人，2010 年，2012 年）。事实上，多年生作物可以提供多种生态系统服务，例如：i) 保持土壤肥力；ii) 与一年生作物相比，增加土壤碳储量潜力（Glover 等人，2010 年；Monti，2012 年）；iii) 通过全年植被覆盖和对比土壤侵蚀加强土壤保护（Durán Zuazo 和 Rodríguez Pleguezuelo，2008 年；Vallebona 等人，2016 年）；iv) 改善农田的生物多样性并保证农业生态系统具有更高的复原力（Peyraud 等，2014）。在地中海，多年生暖季型牧草是生产牧草作为生物能源利用的饲料或原料的有利可图的作物（Monti 等，2012）。此外，在常规生产如牧草或饲料的夏季干旱期，暖季牧草可以提高地中海牧草种植系统的生产力和稳定性（Gherbin 等，2007）。在多年生暖季草中，柳枝稷（Panicum virgatum L.）是一种草原物种，原产于北美，最初被驯化用于牧草生产，因其即使在干旱条件下也能积累大量生物量的能力而得到认可（Monti 等，2012）。从 90 年代开始，由于其高产量潜力，柳枝稷已被引入欧洲，作为生物能源部门的有前途的作物（Parrish 等，2005）。在过去十年中，一些研究强调了低地和高地生态型对地中海环境的适用性（Monti 等人，2008 年，2012 年；Alexopoulou 等人，2015 年；Nassi o Di Nasso 等人，2015 年）。此外，文献证明：i) 在种植第三年之后柳枝稷生产力下降（Alexopoulou 等，2015）；ii) 多次收获系统（每年砍伐一次以上）对种植园寿命产生负面影响（Monti 等，2008）；iii) 柳枝稷产量受施氮 (N) 的影响（Nassi o Di Nasso 等人，2015）。关于这种作物对施氮肥的反应，Ashworth 等人。(2015b) 指出可持续的生产水平（使用生命周期评估方法进行评估）可以通过低施氮量（67 kg ha-1）实现，因为较高的氮量会降低效率 通讯：Giorgio Ragaglini，研究所生命科学，圣安娜高级研究学院，Via Santa Cecilia 3, 56127,