To successfully cultivate sunflowers and help the plants reach their yield potential, the farmer needs to know and control the factors affecting the seed germination and crop establishment.
Planting time and Soil requirements of Sunflower
Sunflower is a highly adapted crop to different environmental conditions and soil characteristics. This allows a higher flexibility in the planting date, something significant when sunflower is used in double planting schemes. Despite its high frost and heat tolerance, it is essential to follow some ground rules to help the plants reach their yield potential.
Seeds can germinate at 6 oC (42 oF), but it is advised to wait and sow when the temperature reaches 10-13 oC (50-55 oF) to achieve faster and more uniform emergence. Early planting and, as a result, the earlier harvest may decrease seeds losses due to birds, while on the other hand, late planting reduces the risk of damage from the sunflower moth (1). However, in any case, the sowing must take place during the suggested period for each crop and region to protect the final yield. The optimum temperature for plant growth is around 21-26 oC (70-78 oF), while temperatures of -3 to -5 oC (26 oF) for approximately 6 hours can kill a mature sunflower plant. From flowering until plant maturity, the temperature level can affect fatty acid production in the sunflower seeds. More specifically, the levels of oleic acid were a bit higher in higher temperatures (2, 3, Regitano et al., 2016).
While the seeds need sufficient soil moisture to germinate, sunflower prefers well-drained soils with high water holding capacity. The plant’s growth is optimum on sandy loam soils with neutral pH (6.5-7.5), but it can also tolerate clay loam or silty clay loam soils. If the soil pH is below 5.5, the farmer can incorporate lime to increase it. Deeper soils in combination with sufficient-high rainfalls can increase the crop’s yield potential.
Sunflower Row spacing
After selecting the variety, the farmer must obtain the seeds to start sowing. Farmers are advised to use high-quality, healthy, and certified seeds to ensure a reasonable and uniform germination rate. Most sunflower seeds have been treated with fungicides to control downy mildew and insecticide, and some seed companies also treat their seeds with molybdenum (4). Sunflower seeds need to have a good contact with the soil to emerge evenly. For this reason, seedbeds should be firm and moist. In no-tillage systems, farmers pay extra attention to covering the seeds with sufficient soil and ensuring good seed-to-soil contact. Soil compaction, especially in sandy soils, could drastically reduce the infiltration of rainfall water into the ground, reducing the moisture level. This condition and the extra strength the young seedlings need to break this crust can cause significant plant emergence and establishment problems. To reduce the risk of such situations, farmers may use a mouldboard plow or chisel plow to prepare the seedbed for sunflower successfully. Such handling will help break the soil crust and destroy the weeds while limiting soil erosion.
It is essential to avoid planting deeper than 5-6 cm (2-2.5 in) for good and uniform germination. This is especially important for confection sunflowers, in which the maximum depth should be 5 cm (2 in). Seeds planted very shallowly will have problems to un-hull and germinating. Sunflower farmers sow deeper in sandy soils and more shallow in heavy clay soils.
The sunflower is a row crop, but the row spacing is not something strictly fixed. The general rule is that the spacing should comply with the (machinery) equipment that the farmer has and, at the same time, leave enough space for the heads to grow. The seeding rate should adjust to the crop’s yield potential, the type of the soil, and the availability of nutrients and water. As a result, reducing the plant population in lighter soils or/and areas with water scarcity (rainfalls or irrigation) is better. Dwarf sunflower varieties can be sown closer together to limit the lodging problems. For confections-type, larger plant distances should be used to leave enough space for the heads to grow and produce seeds of larger size (market requirement). Increased yields have been succeeded with 50-76 cm (20-30 in) row width. However, good results have been obtained with both larger 1 m (40 in) and more narrow rows of 35.5 cm (14 in) (2).
Sunflower Seeding Requirements and Plants Population per Hectare
For oil-type sunflowers, 3 to 4 pounds of seeds per acre will result in having 15,000 to 22,000-25,000 plants per acre. This means that 3,3 kg to 4,4 kg of seeds per hectare will result in having 37.500 to 55,000-62,500 plants per hectare. For the average seed size, 2 kg of seeds per hectare will lead to 30.000 plants per hectare. For confections-type, a plant population of 12,000 and 18,000 plants per acre (30,000 and 45,000 plants per hectare) is more desirable to obtain larger seeds (1). Farmers can use maximum seeding rates in irrigated or high rainfall areas and in high-yielding soils (nutrient-rich). Finally, farmers growing tall varieties with higher yield potential (heavier heads) usually avoid planting rows across the wind drift to reduce the risk of lodging.
The sunflower grower can use any conventional corn planter or precision drill for sunflower sowing. Plateless and air-planters can offer good seed distribution, but conventional planters with appropriate size plastic plates with filler rings may give even better results. Some farmers also use grain drills when no other option is available, but due to low efficiency, this is not recommended (2). Sunflower is also sensitive to compacted soils, so farmers often use tiers with light pressure, compacting the soil only alongside the seed.
Regitano Neto, A., Miguel, A. M. R. D. O., Mourad, A. L., Henriques, E. A., & Alves, R. M. V. (2016). Environmental effect on sunflower oil quality. Crop Breeding and Applied Biotechnology, 16, 197-204.
Sunflower Soil preparation, Soil requirements and Seeding requirements
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