Effects of lucerne genotype on morphology, biomass production and nitrogen content of lucerne and tall fescue in mixed pastures Amel Maamouri A , Gaëtan Louarn A , Fran¸ c ois Gastal A , Vincent Béguier B , and Bernadette Julier A,C A INRA, UR4 URP3F, CS 80006, F-86600 Lusignan, France. B Jouffray-Drillaud, La Litière, F-86600 Saint-Sauvant, France. C Corresponding author. Email: bernadette.julier@lusignan.inra.fr Abstract. Cultivation of legume–grass mixtures ensures a high, protein-rich forage yield with no nitrogen (N) fertilisation. The maintenance of a reasonable proportion of each species over time may depend on the variety. In mixtures of lucerne (Medicago sativa L.) and grass, the effect of genetic variation on biomass and N accumulation is little described. We analysed how lucerne genetic variation affects agronomic traits. The experiment included 46 lucerne and two tall fescue (Festuca arundinacea Schreb.) genotypes tested in microplots of three lucerne and four fescue clones, evaluating biomass production, plant height, stem number and N content in eight cuts in 2011 and 2012. There was a wide genetic variation among lucerne genotypes but no significant statistical interaction between lucerne and fescue genotypes. This suggests that agronomic value of lucerne genotypes for mixtures can be evaluated with any grass genotype. On average, the grass plants grown with highly productive lucerne genotypes had an increased leaf elongation and N status but a reduced tiller number, which could limit their persistence. This is the first observation that the choice of lucerne genotype determines morphology, biomass production and N absorption of both lucerne and tall fescue grown in mixture. Additional keywords: competition,฀ forage,฀ grassland,฀ mixture. Received฀ 19฀ June฀ 2014,฀ accepted฀ 15฀September฀ 2014,฀ published฀ online฀27฀January฀2015 Introduction Agricultural systems face major challenges related to energy saving and environment preservation (Lemaire et al. 2005). Legumes have a crucial role because they are able to fix atmospheric nitrogen (N 2 ) to produce protein-rich feed and to increase soil N content (Garg and Geetanjali 2007). In perennial grasslands, legume–grass mixed cropping is a mode of cultivation in which a part of the N fixed by the legume species becomes available to the grass (Fustec et al. 2010). It is an old and widespread practice that declined in the 1960s because of extensive use of N fertilisers on forage grasses and protein supplementation of ruminant diets with byproducts (soybean meal) (Huyghe et al. 2014). The increase in the cost of energy needed to synthetise mineral N fertiliser and the market demand for protein supplements indicate that forage legume crops have to play a central role in protein supply for ruminants. The performance of a plant (biomass production, N content, survival) in a mixed sward depends on its ability to intercept and use the resources provided by the environment, for example, solar radiation, N, water (Malézieux et al. 2009). Plants compete for resources, and this competition is determined by their morphological and physiological characteristics. Aerial morphogenesis, in particular plant height and vertical distribution of leaf area, influences the interception of solar radiation and the partitioning of water (Louarn et al. 2012). Root morphogenesis largely determines the capture of water and mineral resources. Because competition for light is more uneven than competition for soil resources (Schwinning and Weiner 1998), interception of light is a major driver of the competition between plants. Larger plants proportionally obtain more resources and strongly limit the growth of their smaller neighbours (Schwinning and Weiner 1998). Nitrogen and water, if limited, may also affect plant size, light interception and radiation-use efficiency (Cruz and Sinoquet 1994). In mixed crops, the presence of a legume component (able to fix atmospheric N 2 ) provides additional N to the soil that is available for the plant community. The ability to use different resources from the environment in space and time is a component of complementarity between species (Hooper et al. 2005). Under a cutting regime, two main mechanisms act on N delivery by the legume: exudation of soluble, N-rich compounds by the legume roots; and decomposition of legume dead tissues (roots, nodules, leaves, etc.), making organic N available through mineralisation (Fustec et al. 2010). The relative importance of these two mechanisms and the amount of N delivery depend on the legume species (Louarn et al. 2010). This additional N may be Journal compilation Ó CSIRO 2015 www.publish.csiro.au/journals/cp CSIRO PUBLISHING Crop & Pasture Science http://dx.doi.org/10.1071/CP14164