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Yield Component Comparisons between USA and USSR Winter Wheat Cultivars¹

Information is needed to improve our understanding of the USSR literature regarding cultural and climatic influences on winter wheat (Triticum aestivum L.) production. Effect of seeding rates, N-fertilization rates, and growing season precipitation on tiller formation and grain yield components of winter wheat were investigated by growing one US cultivar (‘Roughrider’) and two USSR cultivars (‘Mironovskaya’ and ‘Bezostaya’) on a Williams loam (fine-loamy mixed, Typic Argiborolls). Plant population densities ranged from 148 to 480 plants/m² as a result of low and high seeding rates. With below average growing season rainfall, grain yield of these cultivars was not influenced appreciably by seeding rate or N-fertilization. Number of tillers and head-producing stems/unit area were about 20% higher on high population density plots than on low population density plots whereas number of kernels/head was about 20% less. With above average growing season rainfall, at respectively 0 and 45 kg/ha of fertilizer N, all high seeding rate plots had about 10 and 20% more heads/m², respectively, than low seeding rate plots. Nitrogen-fertilization alone increased number of head-producing stems about 30%. At high plant population densities, number of kernels/head for Roughrider was 21 and 27% less than at low plant population densities with and without N-fertilization, respectively, whereas both Mironovskaya and Bezostaya maintained higher kernel numbers than Roughrider with only about 8 and 12% respective decrease independent of N-fertilization. Over the 2-year period, grain yields ranged from 1,820 to 4,260 kg/ha. Grain yield could be predicted from leaf area indices at growth stage 10.4 of the Feekes scale (r² = 0.960), from total dry matter production at maturity (r² = 0.835), or from straw production (r² = 0.908). Grain yields could not be predicted from number of tillers/m² or from total dry matter production at any growth stage before maturity. Differences between US and USSR winter wheat cultivars in maintaining kernel numbers at high plant densities are apparently the product of breeding programs conducted under different environments and plant cultures.

Key Words: Leaf area index • Seeding rates • N-fertilization • Tillering patterns • Winterhardiness • Triticum aestivum L.

² Supervisory soil scientists, USDA, ARS, Northern Great Plains Research Center, P. O. Box 459, Mandan, North Dakota, and Northern Plains Soil and Water Research Center, P. O. Box 1109, Sidney, MT.

Received for publication May 11, 1981.