Forage yield and yield components of spring-seeded alfalfa as affected by seeding rate, cultivar and competitive weed species

Ilias S. Travlos

Laboratory of Agronomy, Faculty of Crop Science,  Agricultural University of Athens, 75, Iera Odos st., 11855 Athens, Greece

Established stands of alfalfa (Medicago sativa L.) are fairly competitive with weeds. However, weed competition is one of the most limiting factors during crop establishment and early growth of spring-seeded alfalfa since it is not a vigorous competitor and weeds emerging shortly after seeding can reduce success. Field trials were conducted in 2009 and 2010 in Greece to investigate the effect of several factors on alfalfa productivity within the first, crucial year of establishment. Treatments were a factorial combination of three alfalfa cultivars (Ypati, Gea and Emiliana) seeded at two rates (15 and 40 kg ha^-1) and competed with three weeds (Amaranthus retroflexus, Abutilon thophrasti and Chenopodium album). In each cutting, forage yield and yield components (number of shoots m^-2, shoot height and shoot biomass) were measured. Our study provides evidence that there are significant differences among the several alfalfa cultivars regarding their weed competitive ability and biomass production. The high seeding rate minimized yield loss caused by weeds in all three cultivars. However, in the case of low seeding rates, there were noticeable differences between the three cultivars, with Ypati and Gea being the most and least productive ones, respectively. Forage yield loss was up to 34, 28 and 18% for redroot amaranth, velvetleaf and common lambsquarter, respectively; while the corresponding values were significantly lower at the low crop density, ranging between 3 and 8%. The results of this study confirm the competitive nature of the three above mentioned weeds under Mediterranean conditions, while in parallel they highlight the importance of alfalfa cultivar and seeding rate selection for a successful establishment.