Scientific analysis of how sowing timing and plant density affect sunflower yield in Ukraine's Right-Bank Steppe region
In the Right-Bank Steppe of Ukraine, where drought is not a rarity but a daily challenge, sunflower occupies a dominant position among oil crops. About 80% of its sown areas in Ukraine are concentrated precisely in the steppe regions 2 . Obtaining stable high yields here is not luck but the result of precise calculation. The two most important parameters of this calculation are sowing timing and plant density. They are closely related and together determine how effectively plants use every drop of moisture and every ray of sunlight to form a crop.
of sunflower sown areas in Ukraine are in steppe regions
Sowing timing and plant density determine yield
Drought conditions require precise agricultural practices
Experienced farmers know that focusing on calendar dates can lead to failures. The optimal sowing time occurs when the temperature at the seeding depth (4-6 cm) reaches 10-12°C 3 6 . Under such conditions, seedlings appear in 9-12 days, being uniform and aligned 6 .
For steppe regions of Ukraine, the range of optimal sowing dates is quite long. According to farmers' practice, in Steppe conditions, the best conditions for germination usually occur in late April - early May 2 . Research shows that in Steppe regions, high yields can be obtained with sowing from April 15 to May 27 5 . However, sowing after June 10 leads to significant yield losses and reduced seed oil content 2 5 .
| Soil Temperature at Sowing | "Germination - Seedling" Period (days) | "Seedling - Flowering" Period (days) | Vegetation Period (days) |
|---|---|---|---|
| 8°C | 13-14 | 55-57 | 106-108 |
| 10°C | 11-12 | 55-57 | 104-107 |
| 12°C | 11-12 | 54-57 | 104-105 |
| 14°C | 10-11 | 55-57 | 103-106 |
Establishing optimal density is balancing between maximum use of field resources and preventing competition between plants. Too dense crops (over 70 thousand plants/ha) are inefficient under any conditions: they lead to shading, disease spread, reduction in 1000-seed weight, increased plant height and lodging 2 . Excessively sparse crops create favorable conditions for weed development, and land and resources are underutilized 2 .
Recommended plant density depends on the moisture supply of the region. The higher the soil moisture, the better the conditions for simultaneous seed germination and support of more plants 2 .
| Agroclimatic Zone | Recommended Sowing Rate (thousand seeds/ha) |
|---|---|
| Steppe | 50-55 |
| Forest-Steppe | 60 |
| Polissya | 60-70 |
To ensure the desired pre-harvest density, it's necessary to consider that field germination is 10-20% lower than laboratory germination 6 . Additionally, approximately 8-12% of plants will be destroyed during inter-row cultivation, and another 6-10% may die due to unfavorable growing factors 3 . Therefore, when calculating the sowing rate, it's necessary to include insurance surpluses of 3-7% .
In 2020, under conditions of the experimental field of the Institute of Irrigated Agriculture of NAAS, comprehensive research was conducted to establish the influence of sowing timing, seed treatment and plant density on sunflower yield in Steppe conditions 2 . The experiment was established according to a factorial scheme that included:
8°C, 10°C, 12°C and 14°C
Control (without treatment) and treatment with fungicide-insecticide
40, 50 and 60 thousand plants/ha
The research clearly demonstrated that changing sowing timing affected plant growth and development, altering soil moisture, temperature, field germination and the duration of the "sowing-seedling" period 2 . One of the key conclusions concerned seed treatment. It was found that this measure, depending on the choice of preparation, provides reliable protection against pathogens and pests, which under conditions of the Southern Steppe can destroy 60-70% of seedlings 2 .
| Sowing Timing (Soil Temperature) | Approximate Calendar Dates | Yield (t/ha) | Oil Content (%) |
|---|---|---|---|
| Early (6-8°C) | April 15-17 | 1.74 - 1.76 | 46.6 - 48.3 |
| Optimal (10-12°C) | May 5-7 | 1.76 - 1.74 | 46.5 - 48.4 |
| Late (14-16°C) | May 25-27 | 1.75 - 1.70 | 46.9 - 49.3 |
Modern science and practice use a whole arsenal of means to achieve the optimal ratio of density and sowing timing.
These preparations are the first and most important barrier against diseases and pests. The choice of specific treatment depends on the spectrum of problems characteristic of the region 2 .
Obtaining uniform and aligned seedlings is impossible without even seed placement at the required depth. The speed of the seeder should not exceed 5 km/h, which guarantees accurate seed placement 6 .
Sunflower has a high need for potassium, which increases its drought resistance and oil content. Phosphorus is especially important for root system development at early stages 6 .
Conditions of the Right-Bank Steppe of Ukraine pose complex but solvable tasks for farmers. The key to success lies not in blindly following calendar dates, but in a flexible and creative approach, based on a deep understanding of sunflower biology and local climatic realities.
Tied to soil warming temperature at depth of 10-12°C, provides the foundation for uniform germination and establishment of healthy sunflower plants in steppe conditions.
Within 50-55 thousand plants/ha for steppe conditions, ensures efficient use of available moisture and nutrients while minimizing competition between plants.
As research and practice show, the correct combination of these factors allows minimizing drought stresses, maximizing soil resource use, and realizing the genetic potential of modern sunflower hybrids, ensuring high production profitability even in the most difficult conditions.