Sunflower Fertilizer Requirements

First of all, you have to consider the soil condition of your field through semi-annual or annual soil testing before applying any fertilization method. There are no two identical fields in the world, and thus, nobody can advise you on fertilization methods without considering your soil’s test data, tissue analysis, and field history. However, we will list some standard fertilization programs and options that many sunflower farmers use worldwide.

Sunflower has an extended root system that allows accessing nutrients and water from deeper soil layers compared to other annual crops. This means that the plant can cover most of its modest requirements for the 16 essential nutrients through the environment, decreasing the need for fertilization. However, scientific evidence and practical experience have shown that to reach a higher yield, especially in low fertility soils, the farmer needs to provide sunflower with nitrogen (N), Phosphorus (P), and Potassium (K), in sufficient amounts and at the proper time. It is essential to perform a soil analysis before the crop establishment to determine the nutrient content of the soil for each unique field.

The soil fertility can be used as the first indicator of the plant’s response to fertilization. Indicatively, if there are no limiting environmental factors, fertilization is expected to have a positive yield increase of 80-100% in a very low fertility soil. This number will decrease as soil fertility (the amount of organic matter) increases. The analysis is expected to reveal nutrient deficiencies as well. In most fields, in any climate zone, nitrogen, phosphorus, and sulfur are usually in insufficient amounts for achieving high yields.

Additionally, it is expected to have potassium, calcium, and magnesium deficiency in high-rainfall areas. Other nutrients like boron, iron, zinc, copper, and manganese may also be in shortage in many areas (1). Remember that the soil type is also crucial concerning nutrient availability and mobility. For example, on sandy soils, sunflower often has a higher need for extra potassium fertilizer (2).

Except for this parameter, the farmer should consider some other factors to determine the final type and amount of fertilization. Some of them:

Crop-variety nutrient requirements,
Plant density (population size),
Expected-desired yield, and
Crop rotation scheme (previous crop cultivated in the field)

More specifically, for a production of 2.24 tons of sunflower seed per hectare (2,000 pounds per acre), the plants require approximately the same amount of N, P, and K as 2.70 tons of wheat per hectare (40 bushels per acre). That is roughly translated into 32 N, 11.3 P, 16.8 K, 3.6 S, and 2-3 B kg per hectare (28.6 N, 10.1 P, 15 K, 3.2 S, and 1.7- 2.7 lb per acre) total uptake by the crop (3).

Nitrogen

Nitrogen deficiency is the major yield-limiting factor in sunflowers, especially in poor fertility soils. Some common symptoms of plants lucking N are the delayed and reduced growth, the thinner stems, and the typical general chlorosis of the leaves, which is more prominent in the lower-older leaves. To avoid this situation, the farmer needs to cover the crop needs in N during the entire life cycle of the plants. However, it is essential to avoid over-fertilization, especially in oil-type sunflowers, since it can reduce oil content (4). Furthermore, excessive N fertilization can increase the risk of licking, lodging, and disease (such as sclerotinia).

Apart from their experience, farmers can use specific formulas to calculate the N amounts needed to be added with higher precision. An example is the following (5):

Nrec = (0.05) (EY) – STN(0-24 in.) – NPc

Where:

EY = expected yield (lb./acre)

STN = nitrate-nitrogen ( NO₃-N) measured to a depth of 24 in. (lb./acre)

Npc = amount of N supplied by the previous legume crop (lb./acre).

It is better to spread N application in different doses. Generally, sunflowers have minimum N requirements during the early growth stages, and the N uptake is very low until the 8-leaf stage. However, the farmer can perform small initial fertilization at sowing or pre-planting to avoid any deficiencies during this period. Be careful not to bring in contact the fertilizer with the seeds. Ideally, N can be incorporated into the ground 5 cm (2 in) below the seeds.

Similarly, you can avoid placing ammonium thiosulfate (12-0-0-26) in direct contact with the seed (6). For ammonium and urea fertilizers, soil incorporation (mechanically or by irrigation) is very important. The best results can be obtained when the fertilization is combined with sufficient soil water moisture. It is better to avoid adding the total N amount early in the season, especially in dry sunflowers. The reason is that it can lead to rich leaf growth, reduced water use efficiency, and finally, early leaf senescence that can stress the plants and reduce the yield (shorter time for seed-filling) (7).

A top-dressing application can be performed when the plants have 8-10 leaves and a stem diameter close to 15mm (0.6 in), around 4-6 weeks after planting. The plants absorb 60-100% of the total N from this stage until grain filling. The quantities mentioned above can and should be decreased in fertile soils or/and when sunflowers are planted after legumes. More specifically, the sowing of legumes 2 months before planting the sunflower and incorporating the plants can minimize the need for extra N fertilization (2). The recommended N amounts per hectare are 0-33 kg (0-29.4 lb/ac) after fallow or legume sod, 67.3 kg (60.4 lb/acre) after soybean or small grain crops, and 90-112 kg (80.3-100 lb/ac) after corn or sugar beet (8).

Phosphorus

Depending on the area, the crop, and fertilization history of the field, the amounts of P needed to be applied may vary. The farmer can perform a soil sampling to determine them with better precision. Samples for P and K should be collected during early spring or fall and, of course, not soon after applying fertilizers. The need for P fertilization will be dictated by the bicarbonate extractable P levels on the soil. The plants will benefit from P fertilization only when the soil P availability is below 10-20 ppm or 34 kg per hectare (30.3 lb/ac) (8, 7). Plants lacking phosphate are expected to have reduced growth and probably some dark-grey necrosis in the tips of the lower leaves.

Of course, apart from experience, farmers can use specific formulas to calculate with higher precision the P amounts needed to be added (9). Pre-planting P application is better to be combined with small amounts of N to increase P uptake by the crop. Usually, the total P is applied before or during plantings since it is important for root growth. Some of the P fertilizers used are the dry mono ammonium phosphate (11-54-0) or liquid blends such as 8-24-6 or ammonium polyphosphate (10-34-0). The farmer should keep in mind that by harvesting 454 kg (1001 lb) of seeds, he/she removes from the ground 9-21 kg P₂O₅per hectare (8-18.7 lb/ac). The general advice is to add around 35-200 kg P₂O₅per hectare, (31.2-178.4 lb/ac) depending on the P stored in the soil (7, 3). The farmer should prefer the application in bands and not broadcasted. At the same time, the farmer needs to take action to build up the soil phosphorus content over time.

Potassium

Potassium has a vital role in regulating water use efficiency in sunflowers. Potassium deficiency is not very common since the plants can absorb the needed quantities from the ground. However, this problem is more common in sandy soils, and K fertilizers should be applied when the K-test levels of soil analysis are below 150 ppm. In such cases, some common symptoms are the smaller leaves, with chlorosis (yellowing) on the lower leaves, especially along the margins and the major veins. In some cases, they exhibit upward or downward cupping. K deficiency is more severe when sunflowers are under drought stress and vice versa, especially in older plants. Finally, K deficiency may reduce seed oil content. Generally, very few K amount is removed from the soil with sunflower seed harvest. If the straws are removed from the field, then the K losses increase dramatically, and the fertilization should be adapted correspondingly. The farmer can apply 17-35 kg of K per hectare (15.2-31.2 lb/ac). The amount can be doubled if the fertilizer is broadcast. Usually, the total amount is applied before or during planting since up to 90% of K is used until the flowering stage (3, 7).

References

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

Tags: Sunflower sunflower fertilization

Wikifarmer

Editorial team

Verified

Wikifarmer is a global platform with the mission of empowering farmers through educating them and offering them access to the open market to sell their products at fair prices.

Join our editorial team

Join our community and contribute to Wikifarmer, a platform based on the knowledge of a diverse community of farmers and people working in the agricultural industry from all over the world.

Article submission