Groat Yield and Plant Stand Structure of Naked and Hulled Oat under Different Nitrogen Fertilizer and Seeding Rates

Grain yield of naked oat (Avena sativa var. nuda L.) is lower than that of hulled oat mainly due to reduced seedling emergence, fewer spikelets per panicle, and more grains per spikelet. This study was conducted in the field to evaluate management possibilities of reducing these undesirable traits of naked oat by adjusting seeding rate and N fertilizer application rate, thereby increasing groat yield. Studies were conducted at the Viikki Experimental Farm, University of Helsinki, Finland, in 1993 and 1994. Two N fertilizer rates (80 and 120 kg N ha⁻¹) and five seeding rates (400, 500, 600, 700, and 800 viable seeds m⁻²) were used. Grain and groat yield and 24 morphophysiological traits of three naked and two hulled lines were compared. The highest yielding naked line, Rhiannon, produced approximately 9% higher groat yield and 4% more groat per panicle than the most popular Finnish hulled oat line, Veil. The same groat yield in naked lines and Veli, when measured across all treatments, may result from modest (≈ 2%) differences in seedling emergence. Use of seedling emergence instead of germination percent to determine planting density, and seed treatment with a fungicide, possibly contributed to uniform emergence. Naked lines tillered slightly more than hulled lines, and tiller contribution to leaf area index was higher at lower seeding rates. Use of high seeding rates reduced both number of spikelets and grains per panicle without having consistent effects on number of tertiary grains per spikelet. Number of grains per spikelet was not affected by N fertilizer rate. There was no marked advantage for using higher seeding rates and N fertilizer rates for naked lines. However, the capacity of naked lines to produce panicles through tillering compensates for reduced seedling emergence and an undesirably high grain number associated with a low number of spikelets per panicle.