EFFECT OF SOWING DATES ON THE GROWTH AND DEVELOPMENT OF OILSEED SUNFLOWER VARIETIES

ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 258 UDC 633.854.78 EFFECT OF SOWING DATES ON THE GROWTH AND DEVELOPMENT OF OILSEED SUNFLOWER VARIETIES S.S. Togayeva Associate Professor, Tashkent State Agrarian University Annotation. Sunflower is a major source of edible and technical oils. Ensuring high productivity in sunflower cultivation requires the introduction of high-yielding varieties that are adapted to the soil and climatic conditions of a particular region, along with the improvement of cultivation practices. This article presents the results of a field experiment conducted to study the effect of different sowing periods on the growth, development, and yield of sunflower varieties in the Tashkent region. Introduction.Sunflower seeds contain 50–54% high-quality, semi-drying oil. This oil is widely used directly as food, in the production of fish and vegetable preserves, margarine, bread, and confectionery products. One of the main ways to obtain high profitability from sunflowers is to cultivate early-maturing varieties as a second crop during the summer. Developing modern cultivation technologies that ensure higher and better-quality yields, determining the influence of sowing dates on sunflower productivity, and widely introducing these results into practice are considered urgent scientific tasks. In the southern regions of the Republic, sunflower as the main crop is recommended to be sown during the first and second ten-day periods of March, whereas in central regions it is recommended to sow in the third ten-day period of March or the first ten-day period of April. As a summer crop, sunflower may be sown until June 15 in southern regions and until June 5–10 in central regions [5]. According to N.B. Reymov, in order to determine optimal sowing dates, the best varieties of the Oilseed Crops Research Institute (Russia)—Master, Rodnik, and the standard hybrid Luchafărul— were sown on 15 March, 30 March, 15 April, 30 April, 15 May, 30 May, and 15 June in 2002–2003. In these sowing periods, the Master variety yielded 3.47, 3.51, 3.23, 3.15, 2.94, 2.60, and 2.43 t/ha, while the Rodnik variety produced 2.43, 2.46, 2.24, 2.16, 1.98, 1.95, and 1.91 t/ha, respectively. Early sowing—when the soil warms to 6–8°C in mid-March—is recommended for the Master variety. The Rodnik variety, being early-maturing, can be cultivated as a second crop after the harvest of winter wheat. Late sowing shortens the growing period and leads to an increase in empty seeds, reduced head diameter, smaller seeds, and lower yields [4]. Sowing dates are determined by air temperature, soil moisture, and other environmental conditions. When average air temperature reaches 15°C and the soil sufficiently warms (optimal period), seedlings emerge uniformly. Sunflower is generally sown when soil temperature reaches 3–4°C. It can also be sown as a second crop after winter barley and wheat (D. Yormatova) [2]. Scientific literature indicates that it is necessary to determine sowing dates that ensure high sunflower yields after winter cereals, considering the soil and climatic conditions of each region. Materials and Methods. Field experiments were conducted at the experimental station of Tashkent State Agrarian University. The experiment consisted of 12 variants arranged in four replications. The total plot size for each variant was 56 m², of which the accounting area was 28 m² (25 m long and 2.8 m wide). The total experimental area covered 3,584 m². ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 259 Four sunflower varieties—“Jahongir”, “Rodnik”, “Dilbar”, and “Navruz”—were sown on three dates: 20 June, 1 July, and 10 July. Row spacing was 70 cm, and 50,000 viable seeds per hectare were planted. Mineral fertilizers were applied at the rate of N200P80K60 kg/ha. The preceding crop was winter wheat. Agrotechnical measures for sunflower cultivation were carried out in accordance with accepted recommendations [1, 3]. Results and Discussion. Sowing date plays an essential role in shaping the economically significant traits of sunflower, as it affects the duration of the growing period, weed infestation, soil moisture levels, harvesting time, soil preparation for subsequent crops, and susceptibility to diseases and pests. In the “Jahongir (st)” variety, at the early sowing date of 20 June, plant density at the beginning of the growing season was 47,612 plants per hectare, decreasing to 45,713 plants by harvest. A total of 1,899 plants were lost during the growth period due to various factors. At the 1 July sowing date, 2,356 plants were lost, leaving 45,124 plants by harvest. When sown on 10 July, plant loss decreased to 2,350 plants, resulting in 45,190 surviving plants per hectare. Similar patterns were observed in the other varieties tested—“Rodnik”, “Dilbar”, and “Navruz”. Table 1. Effect of Sowing Dates on Sunflower Seedling Density and Development № Varieties Sowing dates Seedling density, thousand plants/ha Sunflower stem height, cm Number of leaves per plant Leaf area of sunflow er, (thousa nd m² per hectare) At the beginning of the growing period Harvestin g period 1 Jakhongir (st) 20.06 47612 45713 142,4 26,0 22,4 2 1.07 47480 45124 135,8 24,9 21,4 3 10.07 47540 45190 130,6 23,2 20,4 4 Rodnik 20.06 47460 45595 187,9 26,5 22,8 5 1.07 47476 45102 182,0 25,6 22,3 6 10.07 47460 45085 176,2 24,2 21,8 7 Dilbar 20.06 47618 45713 195,9 30,0 24,3 8 1.07 47618 45237 183,1 29,3 23,3 9 10.07 47616 45235 165,8 28,1 22,4 10 Navruz 20.06 47580 45695 185,5 29,2 23,7 11 1.07 47500 45071 179,7 28,2 22,5 12 10.07 47500 44980 142,4 26,7 21,9 In the Dilbar variety, a higher number of surviving plants was recorded across all treatments compared with the other varieties and experimental variants. Relative to the Navruz variety, ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 260 the Dilbar variety retained 18.0, 164.0, and 255 more plants, respectively, across the corresponding sowing dates. Compared with the Rodnik variety, plant survival in the Dilbar variety exceeded it by 118, 135, and 610 plants across the respective sowing dates. Relative to the control variety, the number of surviving plants was identical under the first sowing date, whereas under the subsequent sowing dates, an additional 113 and 45 plants, respectively, were retained It was established that sowing dates exert differential effects on stem development in the sunflower varieties studied. According to the obtained data, the stem height of the control variety Jahongir (st) averaged 142.4 cm under the earliest sowing date (20 June), 135.8 cm under the 1 July sowing date, and 130.6 cm under the latest sowing date (10 July). The lowest value for this variety was observed under the 10 July sowing date (130.6 cm). In the Rodnik variety, the lowest stem height was likewise recorded under the 10 July sowing date, amounting to 176.2 cm. Under the 1 July sowing date, stem height was 5.9 cm lower than in the 10 July variant, and 11.7 cm lower than in the earliest sowing (20 June). The data presented in the table indicate that this variety also follows the same general pattern described above. The stem height of the Dilbar variety exceeded that of the other varieties across all sowing dates. When sown on 20 June, the variety exhibited the greatest stem elongation, reaching 195.9 cm. In the later sowing dates, stem height decreased to 183.1 cm and 165.8 cm, respectively. Compared with the control variety Jahongir (st), the stem height of Dilbar was 53.5 cm lower under the 20 June sowing date, 47.3 cm lower under the 1 July sowing date, and 35.2 cm lower under the 10 July sowing date. Relative to the Rodnik variety, Dilbar exhibited stem heights that were 8.0 cm and 1.1 cm greater under the first two sowing dates. However, under the 10 July sowing date, the opposite trend was observed: the Rodnik variety showed a stem height 10.4 cm greater than that of Dilbar. The stem height of the Navruz variety was generally close to that of Dilbar. Under the 20 June sowing date, it was 10.4 cm shorter; under the 1 July sowing date, 3.4 cm shorter; and under the 10 July sowing date, 23.4 cm shorter result was observed. It was determined that sowing dates exert a substantial influence on leaf development and the number of leaves formed on the stems of the sunflower varieties studied. Early sowing after the harvest of cereal crops led to an increase in the number of leaves per plant. In the control variety Jahongir, an average of 26.0 leaves per plant was recorded under the earliest sowing date (20 June), whereas 24.9 leaves were formed under the 1 July sowing date and 23.2 leaves under the 10 July sowing date. Thus, earlier sowing resulted in 1.0 to 2.0 additional leaves compared with later sowing dates. This pattern was consistent across the Rodnik, Dilbar, and Navruz varieties examined. In the Rodnik variety, 26.5 leaves were produced under the 20 June sowing date, 25.6 leaves under the 1 July sowing date, and 24.2 leaves under the 10 July sowing date. The Dilbar variety produced the highest leaf numbers, with 30.0 leaves under early sowing (20 June), 29.2 leaves under the 1 July sowing date, and 28.1 leaves under the 10 July sowing date. Early sowing increased leaf number by 0.7 to 1.9 leaves relative to later sowing dates. In the Navruz variety, 29.2 leaves were recorded under the 20 June sowing date, compared with 28.2 leaves under the 1 July sowing date and 26.7 leaves under the 10 July sowing date. Across the four varieties, early sowing consistently resulted in a higher number of leaves per plant (26.0, 26.5, 30.0, and 29.2 leaves), while the latest sowing date (10 July) produced the lowest values ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 261 (23.2, 24.2, 28.1, and 26.7 leaves). Among the varieties, Dilbar and Navruz showed greater leaf production compared with Rodnik and Jahongir. According to the research data presented in the table, the leaf area index of the Jahongir variety reached 22.4 thousand m²/ha under the earliest sowing date (20 June). When sowing was delayed until 1 July, leaf area decreased to 21.4 thousand m²/ha, and when sowing was further postponed to 10 July, it declined to 20.4 thousand m²/ha. Thus, relative to the early sowing date, leaf area decreased by 1.0–2.0 thousand m²/ha under later sowing conditions. In the Rodnik variety, leaf area amounted to 22.8 thousand m²/ha under the 20 June sowing date, 22.3 thousand m²/ha under the 1 July sowing date, and 21.8 thousand m²/ha when sowing was delayed to 10 July. For the Dilbar variety, leaf area was 24.3 thousand m²/ha under the 20 June sowing date, decreasing to 23.3 thousand m²/ha under the 1 July sowing date and further to 22.4 thousand m²/ha under the 10 July sowing date. Similarly, in the Navruz variety, leaf area reached 23.7 thousand m²/ha under early sowing (20 June), 22.5 thousand m²/ha under the 1 July sowing date, and 21.9 thousand m²/ha when sown on 10 July. Overall, the results on leaf area per hectare indicate that the highest values in all four varieties— Jahongir, Rodnik, Dilbar, and Navruz—were obtained under the earliest sowing date (22.4–22.8– 24.3 and 23.7 thousand m²/ha). When comparing leaf area indices per hectare across cultivars, the varieties “Dilbar” and “Navruz” demonstrated closely similar values, while a pronounced difference was observed in the cultivar “Jahongir.” According to the obtained results, the leaf area of the “Dilbar” variety exceeded that of “Navruz,” “Rodnik,” and “Jahongir” by 0.6, 1.5, and 1.9 thousand m²/ha, respectively. In the control cultivar “Jahongir,” full maturity was recorded at 103 days when sown on June 20, at 105 days when sown on July 1, and at 110 days when sown on July 10. In sunflower cultivars sown late—on July 10—flowering and maturation phases were delayed by 5–7 days due to decreased air temperature and irrigations during these periods. This pattern was also observed in the sowing dates of the cultivars Rodnik, Dilbar, and Navruz included in the experiment. The cultivar Rodnik is an early-maturing variety: when sown on June 20, maturity occurred at 87 days; when sown on July 1, at 91 days; and when sown on July 10, at 95 days. This variety matured 16 days earlier than the control cultivar Jahongir at the first sowing date, 14 days earlier at the second date, and 15 days earlier at the third date. When the cultivar Dilbar was sown on 20 June, maturation occurred at 100 days; when sown on 1 July, at 103 days; and when sown on 10 July, at 107 days. This cultivar matured 3 days earlier than the control cultivar Jahongir at the first sowing date, 2 days earlier at the second, and 3 days earlier at the third sowing date. The Navruz cultivar was found to develop over a growth period similar to that of the control cultivar Jahongir. Among the cultivars tested, Rodnik proved to be the earliest-maturing variety, reaching maturity 13– 16 days earlier than the other cultivars at the first sowing date, 12–14 days earlier at the second date, and 12–15 days earlier at the third date. The cultivars Jahongir, Dilbar, and Navruz are mediummaturing types, attaining full maturity within 103–110 days. At the early sowing date of 20 June, the control cultivar Jahongir produced a yield of 25.2 c/ha, which was higher than in the later sowing variants. When sown on 1 July, yield decreased to 21.1 c/ha, ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 262 representing a reduction of 4.1 c/ha. At the late sowing date of 10 July, yield declined to 15.7 c/ha, which is 8.5 c/ha lower than in the early sowing and 5.4 c/ha lower than in the 1 July sowing. In the Rodnik variety, sowing on the early date of 20 June resulted in a yield of 27.9 c/ha. When sowing was delayed to 1 July, yield decreased to 22.5 c/ha, representing a reduction of 5.4 c/ha. At the late sowing date of 10 July, yield further declined to 17.1 c/ha, which is 10.8 c/ha lower than the early sowing and 5.4 c/ha lower than the 1 July sowing. The Dilbar variety exhibited the highest yield among all experimental cultivars. When sown on 20 June, seed yield reached 35.8 c/ha. Under the 1 July sowing date, yield decreased to 32.4 c/ha, showing a reduction of 3.4 c/ha. At the late sowing date of 10 July, yield declined to 25.3 c/ha, which is 10.5 c/ha lower than the early sowing and 7.1 c/ha lower than the 1 July sowing. In the Navruz variety, early sowing on 20 June produced a seed yield of 33.9 c/ha. When sowing was conducted on 1 July, yield decreased to 24.9 c/ha, a reduction of 9.0 c/ha. At the late sowing date of 10 July, yield declined further to 21.8 c/ha, which is 12.1 c/ha lower than the early sowing and 3.1 c/ha lower than the 1 July sowing. Based on the results obtained for total yield, it was determined that in all sunflower varieties, the highest total yield was achieved when sown early, on 20 June, while delaying sowing by 10 to 20 days led to a decrease in overall yield. Among the varieties tested, the highest total yield was observed in the Dilbar variety, exceeding that of the control Jahongir variety by 11.6 c/ha, Rodnik by 7.9 c/ha, and Navruz by 1.9 c/ha. The oil content of sunflower seeds was measured using the YMR 1600 apparatus, yielding the following results: in the control variety Jahongir, early sowing on 20 June produced seeds with 58.2% oil content, and delaying sowing had an insignificant effect on seed oil content. Specifically, sowing on 1 July resulted in 58.3%, and sowing on 10 July resulted in 58.1%. This trend was consistent across all varieties and sowing dates included in the experiment. The oil content in the seeds of the Dilbar and Rodnik varieties was found to be nearly equivalent to that in Jahongir and Navruz. However, the Dilbar variety distinguished itself with the highest seed oil content among all experimental varieties. At the early sowing date of 20 June, oil content in Dilbar seeds exceeded that of Jahongir by 1.4%, Rodnik by 0.4%, and Navruz by 1.2%. Conclusion. In the “Dilbar” variety, seedling survival was higher across all experimental variants compared to other varieties. Regarding leaf area per hectare, the highest values for “Jahongir”, “Rodnik”, “Dilbar”, and “Navruz” were observed at the earliest sowing date (22.4, 22.8, 24.3, and 23.7 thousand m²/ha, respectively). The “Rodnik” variety, being early-maturing, reached maturity 13–16, 12–14, and 12–15 days earlier than other varieties for the first, second, and third sowing dates, respectively. “Jahongir”, “Dilbar”, and “Navruz” are medium-maturing, reaching full maturity in 103–110 days. Early sowing on 20 June resulted in the highest total yield across all varieties, whereas delaying sowing by 10 or 20 days reduced yield. Among the tested varieties, “Dilbar” produced the highest total yield, exceeding “Jahongir” by 11.6 c/ha, “Rodnik” by 7.9 c/ha, and “Navruz” by 1.9 c/ha. REFERENCES Uzbek Research Institute of Plant Industry. (2007). Field experiment methods. Tashkent, Uzbekistan: Uzbek Research Institute of Plant Industry. Yormatova, D. (2000). Plant science. Tashkent, Uzbekistan: Author. ISSN: 2582-4686 SJIF 2021-3.261,SJIF 20222.889, 2024-6.875 ResearchBib IF: 9.948 / 2024 VOLUME-5, ISSUE-12 263 Nurmatov, Sh., Azizov, T., Tursunov, L., Anarbaev, I., et al. (2012). Recommendations on highyield cultivation technology for oil crops. Tashkent, Uzbekistan: Turon–Iqbol. Reimov, N. B. (2004). Effect of sowing dates on sunflower yield in the conditions of Karakalpakstan. Scientific-Technical Bulletin of the All-Russian Research Institute of Oil Crops, (1), 30–31, 95–101. 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