Biometrics of grain sorghum as affected by seeding timing

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Purpose. Identify the peculiarities of the phenological stages of growth and development and the formation of biometric parameters of grain sorghum hybrids at different seeding timing in the conditions of the Central Forest-Steppe of Ukraine.Methods. The object of the study was the different genotypes of grain sorghum (Sorghum bicolor (L.) Moench.): hybrids ‘Praim’, ‘Lan 59’ and ‘Dniprovskyi 39’ variety. Seed sorghum was seeded in three terms: the first – at the temperature of the soil at the depth of seeding + 10–12 °C; the second + 13–15 °C; the third + 16–18 °C. Seeding rate was 8 kg/ha at the row spacing of 45 cm. The phenological monitoring of the growth and development of sorghum plants was carried out according to the methodology of state varietal testing of agricultural crops (2001).Results Seeding timing significantly affects the flow of phenological stages. At the beginning of the vegetation, the duration of the interstage period of the seeding–sprouts was affected by the temperature regime and the amount of soil moisture at the depth of seeding and decreased at the second and third sowing periods. The increase in this period in the hybrids ‘Lan 59’ and ‘Praim’ and ‘Dniprovskyi 39’ was followed by the first seeding date. The length of the vegetative period of the sprouts – waxy maturity in the hybrids ‘Lan 59’ and ‘Praim’ for the first sowing date was 120–122 days, for the second – 111–129, for the third – 116–121 days; in the ‘Dniprovskyi 39’ variety – 126, 104 and 120 days, respectively. Observations on the growth of grain sorghum in the period of the sprouts – third leaf showed the slow formation of the above – ground mass, especially at the first and third sowing dates. The height of plants for these dates of sowing in the hybrid ‘Lan 59’ was smaller by 0.5–3.2 cm, in the ‘Dniprovskyi 39’ variety – by 1.1–2.3 cm, in the ‘Praim’ hybrid – by 2.2–3.2 cm in comparison with the plants of the second sowing date. The more intense growth of plants is observed during the period of seeding – leaf-tube formation, and the maximum – in the period oftillering – panicle appearance. This is due to the characteristic biological feature of sorghum, i.e. slow growth in the first period of development (before leaf-tube formation).Conclusions. Biometric parameters of sugar sorghum plants depended on both seeding timing and varietal characteristics. The vegetation period of grain sorghum was reduced as affected by the sowing date and the soil moisture reserves. The increase in the air temperature (the third seeding date) influenced the further development of plants at the period of the sprouts – tillering. In the subsequent stages of plant growth and development, the difference between factors of sowing dates and varietal peculiarities varied within one to three days. The plants were most intensively developed in the case of sowing at soil temperature at the depth of seeding + 13–15 °С, their height during the period of waxy maturity was in the hybrids ‘Lan 59’ and ‘Praim’ 124.7 and 115.0 cm respectively, and 105.3 cm in the variety ‘Dniprovskyi 39’. The overall definition of the duration of cultivation of the studied hybrids and variety indicates that under the conditions of the zone of unstable moisture of the Forest–Steppe, sorghum plants react to the conditions of growth and development, in addition, seeding timing is the main agromomical factor of realization biological potential of the crop.