SEEDING RATE EFFECTS ON TILLERING, GRAIN-YIELD, AND YIELD COMPONENTS OF OAT AT HIGH-LATITUDE

A seeding rate for oat (Avena sativa L.) of 500 viable seeds m(-2) is used in Finland for development of a uniculm stand, and to avoid post- anthesis tillering and subsequent uneven ripening of the crop. Plant b reeding has, however, considerably altered plant height and plant stan d structure, thereby possibly changing tillering capacity. The objecti ve of this study was to assess the contribution of tillers to gain yie ld and morpho-physiological traits comparing an oat landrace cultivar (Jalostettu maatiainen), a modern cultivar (Puhti), and a semi-dwarf L ine (Hja 76416) when grown at 200 to 900 viable seeds m(-2) at increme nts of 100 seeds m(-2). The experiments were conducted at Viikki Exper imental Farm, University of Helsinki, Finland (60 degrees 13'N), in 19 91 and 1992. Increasing the seeding rate significantly increased the n umber of main culms m(-2), but decreased straw length and several yiel d components on the main shoot. Tillers in the semi-dwarf line contrib uted 27% to the grain yield at 200 seeds m(-2) This line yielded highe st at 600 seeds m(-2) which favored a uniculm growth habit, and 98% of grain yield was solely from main panicles. Due to the sensitivity of the landrace and modern cultivar to lodging, no significant effect of seeding rate on grain yield was recorded under favorable growing condi tions (1991). The highest grain yield for them was recorded at 600 to 800 seeds m(-2) with early summer drought (1992). No tiller contributi on to grain yield was observed at greater than or equal to 500 seeds m -L. Following sensitivity to lodging the optimum seeding rate for the longer strawed lines is lower and more dependent on environmental fact ors than that for the semi-dwarf line.