The application of N at the appropriate time and dose can increase oat crop efficiency by increasing grain yield through changes in production components. High doses of N, depending on the genotype and the environment, can result in plant lodging, which can be addressed with the use of growth retardants. The aim of this study was to evaluate the yield components, lodging, and productivity of white oat cultivars cultivated at two planting locations under different N levels with trinexapac-ethyl growth retardant. Two assays (with and without the application of the growth retardant agent) were used in the experiments, which were set up in the region of Londrina and Mauá da Serra, Parana State, Brazil, in a randomized block design with split plots and four replications. The plots consisted of four white oat cultivars (IPR Afrodite, IPR Artemis, URS Corona, and URS Guria) and the subplots of four doses of N (0, 30, 60, and 90 kg ha-1). Plant height, number of panicles per unit area, number of grains per panicle, thousand grain weight, lodging of plants, and grain yield were evaluated. For the conditions under which the experiments were conducted, the growth regulator decreased plant height and lodging. Furthermore, the growth regulator in combination with N topdressing increased the number of panicles per unit area. Thus, the increase in grain yield with the application of a growth retardant was dependent on the characteristics of the plant growth environment. The response of genotypes to N fertilization was also dependent on the soil and climatic characteristics of the environment.

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Initial seed vigor and sowing density interact in establishment of plants in the field, and can thus affect expression of the plasticity of the wheat crop and the yield and physiological quality of the seeds produced. The aim of this study was to evaluate the effect of seed vigor levels in combination with sowing densities on the yield and physiological potential of wheat seeds. The cultivars BRS Gralha-Azul and BRS Sabiá were used in a randomized block experimental design in a 2 × 4 factorial arrangement, with four replications. The treatments consisted of seeds of high and low vigor and four sowing densities (150, 250, 350, and 450 seeds.m-2). The following evaluations were made: seed yield, germination, first germination count, seedling length, seedling dry matter, accelerated aging, emergence speed index, and seedling emergence in sand. An increase in sowing density favors the seed yield of both cultivars; however, it reduces the vigor of the seeds produced by the cultivar BRS Gralha-Azul, especially of the seeds produced by plants originating from high vigor seeds. For the cultivar BRS Sabiá, an increase in sowing density decreases the germination performance of seeds produced by plants originating from low vigor seeds.

The application of nitrogen (N) in the correct dose and at the right time can favor the productivity and quality of wheat seeds. In this sense, the aim was to evaluate the effect of splitting and doses of nitrogen fertilization on the productivity and physiological quality of seeds of wheat cultivars. The seeds were produced at the National Soybean Research Center, in Londrina-PR, in a randomized block experimental design in a 2 × 7 factorial scheme, with four replications. The factors were constituted by two cultivars (BRS Gralha-azul and BRS Sabiá) and seven combinations of doses and splitting of nitrogen fertilization (0 kg ha-1, 40 kg ha-1at tillering, 80 kg ha-1at tillering, 40 kg ha-1at sowing, 80 kg ha-1at sowing, 40 kg ha-1at sowing + 40 kg ha-1at tillering, 20 kg ha-1at sowing + 60 kg ha-1at tillering). The following were evaluated: productivity, germination, first germination count, length and dry mass of seedlings, emergence of seedlings in sand and emergence speed index. The data were subjected to analysis of variance with comparison of means by the F test, between genotypes, and Scott-Knott, between N combinations. The effect of nitrogen fertilization on seed productivity varies with the cultivar. The application of 80 kg ha-1N at sowing favors the vigorof the seeds for BRS Gralha-azul, and the application of 40 kg ha-1N at sowing, or 80 kg ha-1N at tillering favors the production of quality seeds for BRS Sabiá. The inadequate supply of N impairs the physiological quality of seeds produced.

Determination of optimum wheat sowing density, adequate to the genotype and the environment, is essential to avoid lodging and competition between plants, which can reduce seed productivity and quality. In this sense, the objective of this study was to evaluate the effect of seeding density (in cultivars BRS Sabiá e BRS Gralha-Azul) on productivity and physiological quality of seeds of two wheat cultivars. The seeds were produced in the experimental field of the Brazilian Agricultural Research Corporation, in Londrina-PR, at the National Center for Soy Research (Embrapa Soja) in experimental design of randomized blocks in a 2x4 factorial scheme, with four replications. The following evaluations were performed: seed productivity, thousand seeds mass, first count of germination, germination, seedling length, seedling dry weight, accelerated aging, seedling emergence in sand and emergency speed index. In general, the increase in seed density increases seed production and does not alter germination and emergence of seedlings of both cultivars. The cultivar BRS Gralha-Azul proved to be more productive than BRS Sabiá. The increase in seeding density increases seed vigor for BRS Sabiá cultivar and reduces to BRS Gralha-Azul cultivar.