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Species: Helianthus annuus L.
French: Soleil; English: Sunflower; Spanish: Girasol, yerba de sol; German: Sonnenblumen
Origin and diffusion
Sunflower is a plant of American origin: Peru according to some scholars, Mexico according to others. It was introduced in Europe in the early decades of the 1500s (especially as an ornamental plant), however assuming a certain importance as an oil plant only in the eighteenth century. From the second half of the nineteenth century it had a notable diffusion especially in Russia. Today it is widely cultivated worldwide, so much so that it is currently in second place, after soybeans, among the oil-producing plants. In Italy it is present mainly in central Italy. The current selected varieties give achenes containing even more than 45% of oil. The cultivated forms of Helianthus annuus L. are divided into two groups: one suitable for the production of seeds and forage, comprising monocephalic plants and with large achenes, and one for the production of ornamental flowers, characterized by branched and police-fale plants.
Sunflower flower - Helianthus annuus L. (photo Elena Nelli)
The Sunflower is an annual plant of great development, with a long taproot root on which the lateral roots are inserted. The stem can reach considerable heights: in oil varieties up to about 2 meters. The stem is erect and only at maturity does it curve in the terminal part due to the increase in the weight of the inflorescence. The leaves are inserted on the stem, rough on both sides, equipped with a long petiole and of a different shape depending on the position; they are opposite until the 2nd-3rd pair, while later they are alternate. The stalk ends with lymph flowers or calatids, the dimensions of which vary widely (on average 10-40 cm in diameter). This inflorescence is characterized, externally, by a crown of sterile flowers (with large yellow ligules that are improperly considered to constitute the corolla) into which all the other, smaller, fertile, hermaphrodite are inserted; the total number of flowers varies from 500 to 3,000 up to a maximum of 8,000 in non-oil varieties. The flowers open in a scalar way, with a centripetal pattern. After fertilization, an indehiscent dry fruit is formed, called achenium (inaccurately called seed), of variable size and shape (1,000 seeds weigh 60-90 grams). The oil contained in the chenene represents on average 40-50% of the weight of the seed.
Characteristic of the Sunflower is heliotropism, that is, the fact of following the movement of light during the day; this phenomenon, which affects the inflorescence during the development phase and the young leaves, ceases when flowering occurs, so much so that from this moment on most of the flowers remain facing east south-east.
Sunflower field - Helianthus annuus L. (photo Mario Giannone)
Environmental needs and varieties
In the cycle (which can last from a minimum of 85-95 days for new varieties or new hybrids to 130-140 days, up to a maximum of 180, for old populations) the following phases can be distinguished: germination, emergency, leaf formation, differentiation of flower buttons, active growth, flowering, seed formation and filling and maturation.
Despite being characterized by a high water consumption, the sunflower manages, in case of water shortage, to exploit the brightness of the deep layers thanks to the remarkable capillary development of the root system (up to 1.5-2 meters). The sunflower is a typical renewal plant suitable for dry cultivation, in soils with good water capacity and deeply worked in the central regions where summer rainfall is irregular but has a certain consistency. in the southern regions, which are too arid, sunflower can be grown only with the aid of irrigation. It tolerates both low and high temperatures.
As far as the ground is concerned, those that are too loose because they are incapable of retaining water and those that are too heavy, especially if poorly prepared and without structure, should be avoided. The pH should be around 6-7.2.
The varieties and hybrids available on the market today are different and are divided, according to the duration of the biological cycle, into early, medium and late.
Typical renewal plant, it is an excellent wheat preparer. It has a very short spring-summer cycle and leaves the soil in good fertility conditions thanks to the abundant crop residues. Once developed, it has a remarkable ability to suffocate weeds. Between one crop and another it is advisable to leave an interval of 6-7 years. In the center-south it is possible to use sunflower as an interlayer crop (with irrigation). Given the limited penetration capacity of the roots, plowing (generally in summer) at a considerable depth (50-60 cm) or two-layer processing is required. The soil in the first 6-8 cm must be well managed.
In Italy the sowing is carried out in the first half of April in the North, towards the end of March in the Center and no later than the middle of March in the South. The sowing is done in rows 60-70 cm apart, with precision seeder, taking care of the sowing distance so as to have 4 plants per square meter (4-6 kg / ha) without thinning.
The sunflower is demanding in N, slightly in P and very in K. After germination, weeding can be useful. For the fight against weeds we generally resort to weeding, which can be anticipated (winter), in pre-seeding, in pre-emergency or in post-emergency.
Collection and use
Harvesting begins when the spontaneous fall of the floral wrapping carried by the fruit occurs, the brown coloration of the calatid and the complete dryness of the basal leaves and part of the middle ones. Appropriately modified wheat combine harvesters are used. A good production of achenes is around 20-25 quintals per hectare; in very favorable conditions it can reach 35-40 quintals.
From 100 kg of sunflower seeds 35-40 kg of oil are obtained, with a good food value, good shelf life and stability. From the extraction of the oil there is as a residue a very rich protein cake which is used in zootechnical feeding.
Sunflower seeds (photo website)
Adversity and pests
Hail can cause significant damage throughout the vegetative cycle, causing malformations to the stem, lacerations to the leaves and the fall of the seeds when ripe. Also important are the production losses, especially in the South, due to drought.
There are many mycoses that can damage the sunflower, including: downy mildew (Plasmopara helianthi), the carbon rot of the stem (Sclerotium bataticola sin. Macrophomina phaseolina), the rot of the stem and the calatid (Sclerotinia sclerotiorum), rust (Puccinia helianthi), leaf spotting (Alternaria alternata), gray mold (Botrytis spp.), loidium (Erysiphe cichoracearum) and the calatid rot (Erwinia carotovora var. carotovora).
Insects do not prove particularly harmful to the sunflower; those of some importance are the elateridae (Agriotes spp.), the agrotidae (Agrotis spp.), the collemboli (Sminthurus viridis) and the geometrid moth Gymnoscelis pumilata. Birds can cause moderate damage to the crop, especially during the ripening phase.