Yield, harvest, storage of Sunflower

Sunflower Seed and Oil Yield per hectare and acre

Sunflower farmers concentrate all their efforts during the cultivation season to ensure that their crops will manage to reach their potential and produce the maximum yield possible.The yield has increased globally in the past half-century, breaking one record after the other. From 1-1.6 tonnes of seed per hectare (892-1,427 lbm/ac) in 1970, nowadays, the top-yielding countries like France and China report average yields that exceed 2-2.2 t/ha (1,784-1,963 lbm/ac) (1). This yield increase is mainly attributed to the development of new self-fertile, high-yielding hybrids and improved agricultural practices and machinery. It is interesting to mention that wild sunflower or old varieties were self-incompatible. This means that the plants depended on pollinators for fertilization and seed production. The breeding of modern varieties overcame this issue, increasing the yields even without sufficient pollinators. However, even modern sunflower hybrids can be significantly favored by pollination. Scientific reports indicate that yield could increase up to 48.8%, and oil percentage could increase by 6.4 % in bee-exposed hybrids (2). If farmers want to benefit from these insects, they need to use bee-friendly pesticides, spray in the evening, and inform the beekeeper of such actions.

Typically, the average oilseed sunflower yield of an experienced farmer in fertile soil range from 2.3 to 2.5 t/ha (2050-2230 lbm/acre). These numbers are decreased when the crop grows in dry conditions without irrigation and few rainfalls, reaching 0.7-2.0 t/ha (624-1784 lbm/ac). Under irrigation or sufficient rainfalls and soil moisture, an experienced farmer can achieve a crop yield of 4.0 t/ha (3569 lbm/ac). In oil-type sunflowers, in most cases the oil yield can range between 1 and 3 t/ha (892 and 2,2677 lbm/ac) when no limiting factors occur. Record yields of even 5.7 tonnes per hectare (5000lbm/ac) have been reported in certain areas (Toensmeier, 2016).

The final sunflower yield can be affected by the following factors:

the sunflower variety-hybrid
the quality of the seed used for sowing
the environment (temperature, soil, etc.)
the availability of well spread and sufficient rainfalls across the growing season (or the availability of irrigation)
the nutrient availability (soil fertility, field’s crop history, and fertilization program)
the health of the plants (pest and disease management)
the availability of appropriate machinery

The farmer can use many different ways to calculate the crop yield at the end of the season before harvest. One of them is the use of the formula below:

Yield: 2,450 x plant population x head size x seed size x good seed count x center seed set x no bird damage = lbs/acre.

To find more information on how to use this formula, visit the site of NDSU (N. Dakota State University) (3)

Sunflower Harvest

Harvesting Time

Most sunflower cultivars complete their life cycle within 90-120 days after sowing. Of course, this time may vary significantly under different factors (biotic and abiotic stresses, variety, etc.). For this reason, the farmer needs to have another indication that reflects the physiological maturity of the plants and can be used as a harvest signal. The change of color of the back of the head from green to yellow and the bracts to brown usually indicate the sunflower’s physiological maturity. This is the Stage R-9 and happens 30-45 days after bloom, around mid-fall. The seed moisture is still high at 35% (20-50%) at this stage. From that moment on, harvesting can start since no extra yield gain is expected.

On the contrary, the period between maturity and harvest should be kept as short as possible because there is a risk of yield losses due to diseases, bird damage, or wet weather. After maturity, the plants need to dry down, and the seed moisture content needs to be reduced. To accomplish that, some farmers can benefit from early fall frosts or by applying a desiccant. Such products should not be used before the physiological maturity of the crop because they can reduce yield and oil content. At this point it is important to mention that even by using desiccant, the drying of the seeds will be much slower compared to that of the whole plant.

In general, mechanical harvest (by combines) can start with less than 18-20% of seed moisture. However, some farmers prefer to delay harvest until the seed moisture content decreases to 9.5%, allowing safe and direct storage. However, at such low moisture, there is a high risk of seed shattering (2). The farmer should also consider the commercial seed quality prerequisites for the type of sunflower that he/she cultivates. For example, for confection sunflower, contracts usually require 10% moisture, less than 1% sclerotia and dark roast, and 155g/0.5 L (approximately 25 lb/bu) test weight (4).

How to harvest sunflowers and minimize losses

Sunflower can be harvested by hand or mechanically. The second option is of course the most common, especially in commercial crops. For this purpose, farmers can use either combine heads designed explicitly for sunflowers or regular “all crop” platform heads used for threshing small grains like wheat or even for soybeans (5). A variety of header attachments are available, with many operating on a head stripper principle, designed to gather only the heads and eliminate as many stalks as possible. When sunflower has not been sown in rows, the farmer can use the pan header, which is mounted on a traditional straight cut (4).

To minimize the yield losses during mechanical harvest, the farmer needs to know the factors causing them and make some adjustments accordingly. The 3 main reasons for losses during harvest are the (2):

loss in the standing crop ahead of the combine,
header loss as the crop enters the machine and
threshing and separating loss.

Some typical combine settings that can help the farmer reduce the risk of losses during harvest include the following. The combines speed should be around 3 to 5 miles per hour and adjusted accordingly to a moisture content of the sunflower seed, the number of lodge plants, and crop yield. For example, the handler should reduce speed when the seed moisture content is low to avoid shatter losses. Compared to other crops, in sunflower, the airspeed should decrease to avoid blowing the seeds out of the combine due to the lighter seeds. The concave should be run wide open, while the cylinder speed should usually be 250 to 400 rpm. Finally, an upper sieve of 1/2 to 5/8 inch and a lower sieve of 3/8 inch can be used (6, 5).

The farmer should also keep in mind that the lower weight and larger size of sunflower seeds than small grains affect the transportation costs. To have an idea, typical test weights for oilseed sunflowers are around 28-32 lbs./bu, with the U.S. grade standard being even lower (6).

Post Harvest Handling: Drying and Storage of Sunflower seeds

Early harvest, always after the plant’s physiological maturity, may have many benefits. However, the high seed moisture content at that moment makes the storage of the product prohibitive. The seeds need to be dried to ensure a safe and prolonged storage life. The acceptable seed moisture level depends on the storage conditions (temperature, etc.) and the desired storage period. For example, for temporary storage, seeds may have a 12% moisture, while in freezing conditions and sufficient aeration, even a 15% may be acceptable. However, less than 10% moisture is required for more extended storage. Oil-type sunflowers should not be stored above 10 % and 8% moisture during the winter and the summer, respectively. Generally, the higher the seed oil content, the lower the moisture level for better storage (7). Similarly, non-oil seed sunflowers should not be stored above 11 % moisture during the winter and 10 % during the summer (8, 2).

The farmer can mechanically dry the seeds using natural-air, low-temperature, and high-temperature bin, batch, and continuous-flow dryers to reach the desirable seed moisture levels. Depending on the initial moisture, the airflow, and the temperature, the process may last between 3 to 6 weeks. Be careful or avoid using operators accustomed to drying corn or small grains because they over-dry sunflowers. Usually, a drying temperature between 43 and 104°C (110-220°F) is preferred, since it does not have a negative effect on the oil and fatty acid composition. When the temperature is lower, the drying will take longer. For confection sunflower, avoid using a very high temperature that can harm the seeds. For seeds that will be used as a reproduction material, a temperature below 43°C (110°F) must always be used (9).

Drying and cooling sunflower seeds can help preserve their health and quality for a longer period. The harvested seeds usually have a temperature of around 30°C. For storing them, together with the moisture, we need to decrease the seed temperature below 20°C. The storing temperature can be maintained between 10-18°C to slow down the breeding of pests and the spread of fungal diseases. To ensure that, frequent inspection and sampling are needed. The inspection should be performed every 15 days for stored sunflower seeds, compared to once a month for small grains (7). Farm facilities appropriate for storing small grains are also adequate for sunflower seeds. When bin space is limited, as an alternative, the farmer can use polybags to store sunflower seeds (10).

Finally, depending on their commercial use, after storing, the seeds can be (packed) sold directly to the consumers or for oil extraction. You can find more detailed information about sunflower seed preparation and oil extraction here (Le Clef & Kemper, 2015).

References

Ayerdi, G. A., & Larbi, R. (2016). Effects of refining process on sunflower oil minor components: A review. Oilseeds and fats, crops and lipids.

Le Clef, E., & Kemper, T. (2015). Sunflower seed preparation and oil extraction. In Sunflower (pp. 187-226). AOCS Press.

Toensmeier, E. (2016). The carbon farming solution: A global toolkit of perennial crops and regenerative agriculture practices for climate change mitigation and food security. Chelsea Green Publishing.

Sunflower: History, Uses and Plant information

Sunflower Variety Selection

Sunflower Soil preparation, Soil requirements and Seeding requirements

Irrigation of sunflower

Sunflower Fertilizer Requirements

Weed Management in Sunflower Farming

Sunflower pests and diseases

Yield, harvest, storage of sunflower

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