EFFECTS OF SEEDING RATE ON GROWTH DURATION AND ACCUMULATION AND PARTITIONING OF DRY-MATTER IN OATS

Crop management influences considerably the three components of grain yield, growth duration, growth rate, and harvest index (HI). Effects o f seeding rate on these yield components in oats (Avena sativa L.) was assessed in field experiments at the Viikki Experimental Farm, Univer sity of Helsinki, Finland (60 degrees 13'N) in 1991 and 1992. Three Fi nnish oar genotypes were evaluated; a long-strawed landrace cultivar, a moderately long-strawed modern cultivar, and a semi-dwarf breeding l ine. The following traits were measured: grain yield, da)Is from sowin g to yellow ripeness, number of tillers on main shoot, phytomass, vege tative phytomass, and their growth rates (PGR and VGR, respectively), panicle weight and its filling rate (PFR), HI, leaf area index (LAI), and at intervals, dry-matter accumulation in leaves and straw. Increas es in seeding rate significantly decreased growth duration and I)GR of individual plants bur increased PGR on a ground area basis. Seeding r ate did nor, however, affect HI. When seeding rate was increased from 200 seeds m(-2) to 500 seeds m(-2), reductions in vegetative phytomass , panicle weight, VGR, and PFR for individual plants ranged between 20 and 40%, depending on genotype. At greater than or equal to 600 seeds m(-2) differences in these components between seeding rates were mode st. However, PGR, VGR, and PFR per unit ground area increased with inc reasing seeding rates up to 600-700 seeds m(-2). Moreover, the higher the seeding rare, the higher the peak LAI (2.7 maximum) and the earlie r the canopy closure. Hence, our results showed that a seeding rate of 600-700 seeds m(-2), which resulted in uniculm growth habit, is advan tageous in terms of grain yield at high latitudes due to higher biomas s accumulation and subsequently greater interception of PAR.