Growth dynamics and agronomic-economic benefits of pea–oat and pea–barley intercrops Christos A. Dordas A,D , Dimitrios N. Vlachostergios B , and Anastasios S. Lithourgidis C A Labaratory of Agronomy, Faculty of Agriculture, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece. B National Agricultural Research Foundation (N.AG.RE.F.), Fodder Crops and Pastures Institute, 413 35 Larissa, Greece. C Department of Agronomy, Aristotle University Farm of Thessaloniki, 570 01 Thermi, Greece. D Corresponding author. Email: chdordas@agro.auth.gr Abstract. Pea (Pisum arvense L.) is an important legume in many areas of the world, which is used for forage and grain production and could be used in intercropping systems. Intercropping of pea with oat (Avena sativa L.) and barley (Hordeum vulgare L.), in two seeding ratios 60 : 40 and 80 : 20, was compared with pea and two cereal monocrops for two growing seasons (2008–10), at the Aristotle University of Thessaloniki, Greece. The effect of the intercropping systems was determined on growth rate, plant height, chlorophyll content, DM, and N yield. Also, several competition and economic indices were used to evaluate the intercropping systems, such as land equivalent ratio (LER), relative crowding coefficient (K), aggressivity (A), competitive ratio (CR), actual yield loss (AYL), system productivity index (SPI), monetary advantage index (MAI), and intercropping advantage (IA). Growth rate of pea and cereals was lower by an average of 39 and 64%, respectively, in the intercrops than in the monocrops. DM yield was the highest in barley monocrop (13.00 Mg ha –1 ) followed by P 80 O 20 intercrop (11.73 Mg ha –1 ). Pea monocrop, and P 80 O 20 and P 80 B 20 intercrops showed the highest crude protein (CP) concentration (137, 132 and 130 g kg –1 DM, respectively), whereas P 80 O 20 intercrop also produced the highest CP yield (1552 kg ha –1 ). The LER, K, and AYL values (average 1.09, 1.75 and 0.29, respectively), were greater for both pea–oat intercrops compared with the pea–barley intercrops (average 0.98, 0.92 and 0.06, respectively), indicating that in these systems there was an advantage of intercropping for exploiting the resources of the environment. The A, CR, and partial AYL values in all intercrops were greater for oat and barley than pea, which indicated that cereals were more competitive partners than pea. The highest MAI, IA, and SPI values were recorded for P 80 O 20 followed by P 60 O 40 intercrops indicating that these intercropping systems were the most profitable. The results from this study showed that both pea–oat intercrops were more productive with high CP yield, and also they showed the best land-use efficiency. Additional keywords: aggressivity, competition, forage, intercropping advantage, LER, monetary advantage. Received 15 July 2011, accepted 3 February 2012, published online 7 March 2012 Introduction Intercropping includes the simultaneous growing of two or more species in the same area for a significant period of time, but without necessarily being sown and harvested together. Intercropping is a practice that is used in low-input cropping systems especially in the developing countries (Lithourgidis et al. 2011a). However, there is a growing interest in many developed countries for using different intercropping systems because of serious problems caused by the intensification of the modern agriculture. Intercropping systems have several advantages such as improved soil conservation, control of weeds, insects, or diseases, improved yield stability of cropping systems, better water and nutrient-use efficiency (Hauggaard-Nielsen et al. 2001; Agegnehu et al. 2006; Vasilakoglou et al. 2008). Cool season grasses intercropped with legumes for forage and silage production are used in many areas of the world. Generally, intercropping legumes with cereals increases protein yield compared with cereals alone (Caballero et al. 1995; Carr et al. 2004). However, there are contradictory data about the productivity of intercropping systems. In particular, many studies reported that intercropping legumes with cereals provided more efficient utilisation of the available resources and increased productivity compared with each sole crop (Izaurralde et al. 1990; Hauggaard-Nielsen et al. 2001; Agegnehu et al. 2006). On the other hand, in some studies there was no significant effect on forage yield (Lithourgidis et al. 2007, 2011b), whereas in other studies intercrops yielded lower DM as compared with cereal monocrops (Caballero et al. 1995; Lithourgidis and Dordas 2010). Seeding rates are very important for an intercropping system as it affects its productivity. Carr et al.(1998) used three pea planting densities in intercrop combinations with Journal compilation Ó CSIRO 2012 www.publish.csiro.au/journals/cp CSIRO PUBLISHING Crop & Pasture Science, 2012, 63, 45–52 http://dx.doi.org/10.1071/CP11181