Wheat Fertilizer Requirements

Wheat Fertilizer Plans and Common Methods

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 farmers use worldwide.

High-yielding modern varieties have a higher N use/utilization efficiency, which means that they absorb and exploit better the available N. However, farmers should keep in mind that the grain yield and the protein content of the grain are negatively correlated. As a result, farmers should adjust the N fertilization timing and amounts in the best possible way to keep a desirable balance between the two.

The fertilization aims to offer wheat plants the appropriate type and amount of nutrients needed to grow and produce high yields sustainably. In order to form the fertilization schedule, the farmer shall discuss with the agronomist and take into account the following:

• The variety that will be cultivated
• Expected yield
• Soil characteristics
• Soil Nutrient 
• Sowing date
• Amount of irrigation and rainfalls

In general, for best growth and yield, wheat plants need the following nutrients: Nitrogen (N), Potassium (K), Phosphorus (P) (Phosphate = PO₄³⁻), Sulphur (S), Magnesium (Mg), Iron (Fe), Μanganese (Mn), Zinc (Zn), Boron (B), Copper (Cu), Calcium (Ca).

Nutrient requirements in different wheat growth stages

N – Nitrogen 

As it happens in many crops, nitrogen and water are the main factors affecting the final yield of wheat. However, the farmer should keep in mind that for the highest yield and best grain quality, an appropriate fertilization program with fertile soil should cover the wheat’s demands in all the different nutrients needed. Based on FAO, 25kg (55.12 lb) of N are usually required to produce 1 tonne of wheat grain per hectare (1). 

The N amounts needed to be added can be calculated with the soil nitrate test equation (2). 

Nrec = (2.5) (EY) – STN (0-24 inc) – Npc

Where:  EY = the expected yield (bushels per acre)

               STN = nitrate-nitrogen measured to a depth of 24 inches (=60cm)(lb per acre) 

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

The Npc depends on the previous crop cultivated in the field and the density of the plants. This number could vary between 20 to 30-40 lb of N per acre (= 22.4 to 33.6-44.8 kg per hectare). 

To convert the above, we remind that:

1 lbs = 0.4536 kg

1 inch = 2.54 cm

1 acre = 0.4046 hectares

1 wheat bushel = 60lbs =27.216kg

Calculating the N needed will help form a more specialized fertilization program for each field crop. However, farmers usually fertilize by experience or following published recommendations. Usually, in each country or region where wheat is a major crop of interest, the governments or institutions publish recommended amounts of N needed. In general, depending on the soil fertility (organic content of the ground), the total N amount required to be applied with fertilization varies between 20 to 120 kg per hectare (17.8 to 107 lb per acre). 

The total amount of N fertilization in spring wheat is usually around 10-20% higher than in winter wheat since the desirable protein grain content is about 1-1.5% higher (3). On the contrary, for Durum wheat, farmers can follow the recommendations for winter wheat.

The recommended or calculated amounts of total nitrogen fertilizer added to the crop can be split into 2-3 applications. While application in one dose is quite usual in rainfed wheat fields, experience and scientific evidence have proven the efficiency and higher yields achieved by splitting the N amount into 2-3 doses across the growing season (4).

The 1st application could be right before or during the sowing of the seeds, with 35-50% of the total amount of N . When wheat follows a soybean crop or well-fertilized corn crop, the extra nitrogen needed to be applied is limited. If the previous case is not true, then a 4-7 kg of N per hectare (3.6-6.2 lb per acre) application could be enough. In sandy soils or late-sowing, the initial N-fertilization could be increased.

If the farmer wants to use ammonium thiosulfate (12-0-0-26) for the first application, it is essential to avoid the contact of the fertilizer with the seeds. Similarly, there is a high risk of damaging the seeds by bringing them in contact with large amounts of urea (46-0-0), especially in dry soils. To avoid this, if the application of urea and sowings need to happen simultaneously, you can keep the amount of urea less than 1.8 kg per hectare (1.6 lb per acre), or irrigate the field before that. In insufficiently wet field, the amount of urea in contact with the seeds can be raised to 13.7kg per hectare (12.2 lb per acre) without causing any germination problems (2). Farmers could apply 2-3 tonnes of manure per hectare (or compost and other organic matter) 5-6 weeks before sowing as an alternative to chemical-synthetic fertilizers. A shallow plowing or/and rainfall or irrigation could be helpful at that time to incorporate it.

The 2nd-3rd N applications could be during crown root initiation, tillering, or stem elongation stage. It is preferred to apply the fertilizers together with irrigation. An application during that period will accelerate the vegetative growth of the plants but could make them more susceptible to lodging. For higher grain yield and protein, it is often recommended to apply N a bit later, during the head development. Based on experimental results, the application of liquid urea ammonium nitrate solution (28 or 32%) 2 to 5 days after anthesis has been shown to increase grain protein. As an alternative, a foliar N fertilization around the anthesis stage could “do the trick,” boost ear formation, and increase protein content. More specifically, research has sown that an application of 5-6 kg per hectare (4.5-5.3 lb per acre) can raise protein by 0.5 to 1% (2)

Nitrogen in wheat farming is important for one more reason: Nitrogen fertilizer reduces the Impact of Sodium Chloride on Wheat Yield. According to a study (6), spike length, number of spikelets, number of kernels per spike, kernel weight per spike, and 1000 kernel weight were affected by interactions between variety and N and by interactions between salinity and N. At the 7.6 dS/m salinity level, the application of 210 kg N per hectare resulted in the increase of  yield by 54.7%.

Phosphorus (P) – Potassium (K)

P and K are the two most important nutrients after N for wheat cultivation. Usually, the total P and K fertilizers are added to the crop at sowing. Usually, most of them are controlled released fertilizers to reduce nutrient leakage and offer better results. A common composition of a synthetic fertilizer for the three main nutrients (NPK) that is used for the first fertilization at sowing is 20-10-0, 24-40-0, 30-15-0, 30-15-5, etc.

Phosphorus is generally applied as phosphate (PO₄³⁻), and a typical amount needed for maximum yield is around 20-40 kg of P per hectare (17.8-35.6 lbs. per acre). P Application with amounts closer to the highest recommended limits may be needed in acidic soils (Rutter et al., 2017). Since phosphate has no negative effect on seed germination, it can be applied with the seeds during sowing. The absorption of P from wheat plants is optimum at 18-25°C. The element is absorbed by the plant and is transferred to the ear during grain filling where the demand is higher. Sufficient amounts of P in the plant, combined with N fertilization, can help in yield maximization. However, overuse of phosphorus fertilizers, especially during winter, may result in a reduction of the freezing tolerance of wheat plants as well as the grain protein content and zinc bioavailability (Gusta et al., 1999, Zhang et al., 2017).  Application of P may also be important on No-Till systems. According to a study (8), if soil P is deficient in a No-Till production system, applying fertilizer P on the soil surface will help alleviate P deficiency even without incorporation. Applying fertilizer P on the soil surface without incorporation will, however, increase the risk of P loss in surface runoff water.

Potassium is most needed from the wheat plant early in its growth and during the stem and head developmental stages. No extra K fertilization is needed when the soil test for K is 161 ppm or higher. Usually, when in deficiency, the added quantities of K₂O can reach 2-7kg per hectare (1.7-6.2 lb per acre) (2). The amounts could be a bit higher for sandy soils. P plays an important role in the starch formation, the mobilization of carbohydrates, plant vigor, and photosynthesis and assists grain filling. P can also be applied with foliar fertilization. Experimental data have sown that foliar application of dilute solutions of potassium orthophosphate (KH₂PO 10 kg/ha or 8.9 lb/ac ) may delay leaf senescence caused by heat and drought, keeping leaves photosynthetically productive for longer. This will result in a yield increase (Benbella and Paulsen, 1998).

S – Sulfur

Sulfur (or Sulphur) is an essential nutrient in wheat crops for two main reasons. First, it affects the Nitrogen Use Efficiency of the plants. That means that deficiency of S in the soil will result in reduced absorption-use of N from the plants. Years of irrigation and lack of S-fertilization have led many soils (35-80%) to “suffer” from S deficiency. However, nowadays, most N fertilizers used have a sufficient amount of S. A typical example is the 40-0-0 (14 SO3). Based on general guidelines for wheat, S content in plant tissue is 0.4%. Additionally, S plays a key role in wheat grain quality, especially when they will be used for bread production. This is because S is an important component of protein formation (Hřivna et al., 2015).

S cannot be mobilized inside the plant. For this reason and due to the S-N positive interaction, S should be added in smaller doses (more than one application) in different growth stages, when needed, and together with N-fertilizers. The amount of S (in SO3 or SO₂−₄ mode) that wheat needs are around 3-5kg per hectare (2.6-4.4 lb per acre) (2). S needs could also be covered by using Manganese sulfate (MnSO₄) in 2-3 foliar applications, close to the first irrigation (2.5 kg MnSO₄ in 500 liters of water). Finally, wheat plants are supplied with S by Zinc sulfate (ZnSO₄), which is usually applied at 25 kg per hectare (22.3 lb per acre)(5). Of course, the farmer should perform soil-plant tissue analysis and adjust the S amounts.

However, these are just some general guidelines that should not be followed without making your own research. 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.

References

1. https://www.fao.org/3/Y4011E/y4011e06.htm
2. https://extension.umn.edu/crop-specific-needs/wheat-fertilizer-recommendations#nitrogen-recommendations-1084760
3. https://www.montana.edu/news/11207/spring-nitrogen-fertilizing-for-optimal-wheat-production
4. http://www.uky.edu/Ag/Wheat/nitrogen.html
5. https://iiwbr.icar.gov.in/wp-content/uploads/2018/02/EB-52-Wheat-Cultivation-in-India-Pocket-Guide.pdf
6. https://www.academia.edu/39091586/Nitrogen_Fertilizer_Reduces_the_Impact_of_Sodium_Chloride_on_Wheat_Yield
7. https://www.academia.edu/26485265/Response_of_wheat_to_foliar_application_of_urea_fertilizer
8. https://www.academia.edu/62982352/Fertilizer_Phosphorus_Management_Options_for_No_Till_Dryland_Winter_Wheat

Benbella, M. & Paulsen, G.M. 1998. Efficacy of treatment for delaying senescence of wheat leaves. II. Senescence and grain yield under field conditions. Agron. J., 90: 332-338.

Gusta, L. V., O’connor, B. J., & Lafond, G. L. (1999). Phosphorus and nitrogen effects on the freezing tolerance of Norstar winter wheat. Canadian journal of plant science, 79(2), 191-195.

Hřivna, L., Kotková, B., & Burešová, I. (2015). Effect of sulphur fertilization on yield and quality of wheat grain. Cereal Research Communications, 43(2), 344-352.

Rutter, E. B., Arnall, D. B., & Watkins, P. (2017). Evaluation of Phosphorus Fertilizer Recommendations in No-Till Winter Wheat.

Zhang, W., Liu, D., Liu, Y., Chen, X., & Zou, C. (2017). Overuse of phosphorus fertilizer reduces the grain and flour protein contents and zinc bioavailability of winter wheat (Triticum aestivum L.). Journal of Agricultural and Food Chemistry, 65(8), 1473-1482.

Wheat Plant Information, History and Nutritional Value

Principles for selecting the best Wheat Variety

Wheat Soil preparation, Soil requirements, and Seeding requirements

Wheat Irrigation Requirements and Methods

Wheat Fertilizer Requirements

Wheat Pests and Diseases

Yield-Harvest-Storage of Wheat

Weed Management in Wheat Farming