History of the development of the sunflower crop and morphological features of the plant

From ornamental flower to global oil crop

The origin of the sunflower (Helianthus annuus L.) is the south of North America, where it began to be cultivated about 3,000 years BC. Native Americans used ground seed as flour, whole seed as a treat, and oil for baking as well as for skin and hair care. The crop was brought to Europe by Spanish conquerors in the 16th century, initially used as an ornamental and medicinal plant.

The first patent for sunflower oil production was obtained by the English in 1716; however, large-scale industrial extraction began in Russia. After the seed was brought from Holland, the plant remained ornamental for a long time. In 1828, a serf peasant from the village of Alekseevka applied the technology for obtaining linseed and cedar oil to the sunflower. As early as 1833, the village owner, with the assistance of the inventor, built the first oil mill, and the new product quickly gained popularity, as its consumption was permitted during Lent.

By the middle of the 19th century, the sunflower occupied 30–40% of the sown area in the Voronezh and Saratov governorates. Later, thanks to the work of Soviet breeders, it was possible to significantly increase the oil content of the crop and its resistance to pests. Today, the sunflower is cultivated all over the world, and at the end of the 19th century, Russian emigrants brought the oil production technology back to the plant's homeland — the USA and Canada.

Morphology and economic classification of the crop

The sunflower belongs to the Asteraceae family and is divided into wild and cultivated species. The latter includes ornamental and commercial subspecies. The plant is cross-pollinated and perfectly adapted to finding moisture due to a powerful taproot system. The main root is formed from the embryonic radicle and is densely covered with small lateral branches penetrating a large volume of soil.

• World sown area — more than 18 million hectares
• Root penetration depth — 2.0–2.5 m
• Stem height — 1.0–2.5 m
• Number of florets in the head — 600 or more
• Growing season — 80–140 days

The rigid sunflower stem is filled with spongy pith and usually does not branch. The leaves are ovate-cordate, with serrated edges, on long petioles; the lower 2–3 pairs are arranged oppositely, the rest — alternately. The inflorescence is a head with green bracts along the edge, large orange-yellow ray florets on the periphery, and bisexual tubular florets in the center. The crop's fruit is an achene with a lignified pericarp that does not fuse with the seed.

Agroecological requirements and soil preparation

Seed germination of the sunflower in moist soil begins at a temperature of 4–6 °C. To obtain uniform and healthy seedlings, it is necessary to wait for the seedbed to warm up to 10–12 °C. Swollen seed can tolerate short-term cooling down to −10 °C, and young seedlings are capable of withstanding frosts down to −6 °C.

The heat requirement depends on the length of the growing season of a specific sunflower cultivar or hybrid. For early-maturing forms, the sum of active temperatures is 1850 °C, for early-ripening ones — 2000 °C, and for mid-maturing ones — 2150 °C. The plant consumes about two-thirds of the total heat during the period from emergence to flowering, and the remaining third — during ripening.

The sunflower tolerates heat and drought well due to its deep root system, stem pubescence, and the adaptation of stomata to constant transpiration. However, there is a critical period in its development: from head formation to the end of flowering, the crop consumes about 60% of the entire seasonal moisture rate. For normal growth, the plant requires good lighting, as its development is strongly inhibited in the shade and during prolonged cloudy weather.

Chernozems (sandy loam and loam), chestnut soils, and alluvial soils of flooded river valleys are considered the best for sunflowers, provided they are freed from meltwater early. The optimal soil acidity level lies in the pH range of 6.0–6.8. Field preparation begins in the autumn with stubble cultivation, ploughing, or deep loosening. In the spring, pre-sowing cultivation is carried out, supplemented by early cultivation with harrowing on heavily weed-infested areas.

Organic (15–20 t/ha) and mineral fertilizers are applied before the main ploughing. Sunflower requires the most nutrients during the period from head formation to flowering. The volume of nutrient removal for the formation of one ton of seed is shown in the table below.

Sowing, crop maintenance, and harvesting

For sowing, calibrated seed of regional cultivars is used, treated with the seed treatment agent fentiuram for disease protection. The quality of planting material is strictly regulated according to cultivar categories and classes. Only seed of at least category II and class 2 is allowed for production; in certain cases, it is permitted to use seed of category III and class 3.

Sowing is carried out in early to mid-terms when the soil at the sowing depth warms up to 8–12 °C. Wide-row, single-seed (precision), or check-row (in heavily weed-infested fields) sowing methods are applied with row spacings of 70 and 90 cm. During the sowing campaign, herbicides are also applied to the soil. To eliminate the problem of empty grains, bees are brought to the fields for pollination.

• Soil temperature for sowing — 8–12 °C
• Seed sowing depth — 6–10 cm
• Plant density — 20–50 thousand/ha
• Density under irrigation — up to 60 thousand/ha

Crop maintenance includes a series of mechanical operations to control weeds and break the soil crust. Consistent execution of these operations allows for the preservation of soil moisture and the destruction of weeds at early stages of development. All inter-row tillage is stopped when stem height reaches 60–70 cm.

1. Pre-emergence harrowing — 4–5 days before emergence to destroy weeds and break the crust.
2. Post-emergence harrowing — across the rows upon the formation of 1–2 pairs of true leaves.
3. First inter-row cultivation — to a depth of 6–8 cm.
4. Second inter-row cultivation — to a depth of 8–10 cm.
5. Third inter-row cultivation — to a depth of 6–8 cm.

Harvesting begins when 80–90% of the heads turn yellow-brown or brown in color, and seed moisture decreases to 12–17%. Harvesting is carried out by the direct combining method. The subsequent storage regime for the harvested crop depends directly on its moisture content.

• Batches with 8–10% seed moisture are stored in bags.
• High-oil cultivars are put into storage at a moisture content of no more than 7% in layers up to 1 meter high.

Parallel to sunflowers, rapeseed plays an important role in the structure of oilseed production. According to data from 2005, it accounted for almost 15% of the world's total volume of vegetable oils. In Belarus, rapeseed is a relatively new but promising crop: the first farms started growing it for oil after 1985, and by 2001, crops occupied 129 thousand hectares (2.5% of the total structure).

The state program provided for the expansion of the area under rapeseed by 2010 to 10–12% of all arable land, primarily through the sowing of winter and spring rapeseed and winter rapeseed (turnip rape), which can be successfully grown on less fertile and light soils and on peatlands. In 2006, the production of rapeseed in Belarus amounted to 180 thousand tons, i.e., it increased 3.5 times since 2003, with the crop's yield increasing by 22%.

Rapeseed is a valuable oil crop. Rapeseed seeds contain 32–50% oil and up to 23% protein. Rapeseed oil is semi-drying, and if it is obtained from cultivars that do not contain erucic acid, which gives it a bitter taste, through cold pressing, it is not inferior in quality