Wheat Soil preparation, Soil requirements, and Seeding requirements

Wheat is a widely adaptive crop and does not have very strict soil requirements to grow.  There is a great variety of wheat cultivars, with the main classification to be the time of the year that they will be sown in the field. In this context, wheat varieties are grouped into winter- and spring- types. Each type has different needs and behavior regarding environmental conditions. 

Temperature and soil requirements for wheat cultivation

Temperature

Winter wheat exhibits high resistance to low temperatures (even -20 ^oC or -4 ^oF) during the early developmental stages. In fact, under long-day conditions (the day lasts longer than the night), such conditions are necessary for the normal heading of wheat plants. This process is called vernalization. Spring wheat is more sensitive to low temperatures, and the sowing date should adjust to avoid frost damage in areas with late, strong spring frosts.

• The minimum temperature for germination initiation is 4 ^oC (39.2 ^oF), with an optimum range between 12 and 25 ^oC (53.6 and 77^oF). The germination is accelerated when the temperature is close to 18-20 ^oC (64.4-82.4 ^oF).
• In both types, vegetative growth stops when the temperature drops below 5 ^oC (41 ^oF), while a daily temperature of 15-22 ^oC (59-71.6 ^oF) is needed for optimum growth and tillering. Temperatures of 20-23 ^oC (68-73.4 ^oF) will lead to plants’ accelerated growth. However, in this case, to avoid the exhaustion of the plants, the farmer may take action and offer them the water and nutrients needed to cover the higher demand.
• The stage of anthesis is critical for the final yield, and extreme temperatures with strong wind can cause head sterility, affecting ovary development, pollen, and floret viability. Even the max. and min. threshold temperatures may vary depending on the variety; generally, for anthesis, 4-6 ^oC (39-42.8 ^oF)are the minimum temperatures, while 19-22 ^oC (66.2-71.6 ^oF) are the maximum (Kumar et al., 2016). However, there are specific winter wheat varieties with higher heat tolerance, but even in this case, a temperature exceeding 32-35 °C (89.6-95 ^oF) is considered catastrophic (Marcela et al., 2017). During flowering, if there are warm winds; problems may occur even in lower temperatures. Farmers should consider the temperatures expected around the time wheat enters into flowering and adjust the sowing date accordingly.
• Finally, for the stages of milk, dough, and maturity, the minimum temperatures are 8-10, 11–12, and 13–15 °C (46.4-50, 51.8-53.6, and 55.4-59 ^oF), while the maximum is 24–26.5, 26–29, and 29.5–31 °C (75.2-79.7, 78.8-84.2 and 85.1-87.8 ^oF), respectively (Kumar et al., 2016).

Wheat Soil Requirements 

Wheat can be cultivated in various soil textures. However, medium texture soils are considered best, while peaty soils with high amounts of minerals (sodium, iron, and magnesium) should be avoided (Mojid et al., 2020, 1). Soil texture can influence plant height, leaf area, plant biomass, and grain number and characteristics. 

Wheat is better to grow in a neutral soil pH (around 7). However, the excessive and chronic use of nitrogen fertilizers has led to acidification of most soils where wheat is cultivated. The most cost-effective way to increase soil pH is the application of agricultural limestone.  

Additionally, soils of low fertility and high salinity can negatively affect yield. Salinity problems are more often in irrigated fields. High soil salinity can decrease the survival of wheat plantlets, the number of primary and secondary tillers, the number of leaves and spikelets, as well as the water availability (2). The farmer can help his/her plants by increasing the K+ and decreasing Na+ (Rahman et al., 2005). Finally, salinity levels that exceeded 100mM of NaCl significantly reduced grain quality (Farooq and Azam, 2005). Farmers can collect samples from their fields and send them for analysis to determine and monitor soil characteristics. For soil pH, you can collect representative samples from different areas of your field, of topsoil, and from the depth of 10-20 cm (3.9-7.9 in) and 20-30 cm (7.9-11.8 in). For nutrient testing, the samples should come from 0 to 10-25 cm (0 to 3.9-9.8 in) in depth (3). 

Soil preparation and sowing of wheat

Soil preparation

To have a fast and uniform plant emergence and crop establishment, farmers should purchase certified seeds and prepare the seedbed (field). The ICAR (Indian Agricultural Research Institute) mentions the advantages of bed planting techniques application in light soil, especially in areas with water scarcity, as 30% of water can be saved (3). Wheat can be successfully established in conventional, minimum tillage, and no-till systems. 

Minimum and no-tillage systems have become increasingly famous and preferred since they protect the soil structure, retain soil moisture, and reduce susceptibility to cold temperature damage (winter kill). In no-tillage systems, winter wheat seeding can be performed in residues of barley, canola, alfalfa, and early maturing soybean (4). Generally, seeding in a field with crop residues from the previous wheat crop is not advised since the risk of disease transmission to the new crop is relatively high. 

In conventional tillage systems, the farmer usually performs 1 to 4 ploughings during summer and planking right before winter wheat sowing. For primary tillage and soil preparation, the farmer can use rotary tillage (9) One Pre-sowing irrigation might be needed in some cases. 

Wheat seeds can be sown either by hand or by a great variety of seeders that exist in the market. To achieve a more uniform seed dispersal in the field, machine seeders (air seeders)  are preferred. In this case, depending on the seeder, there is the option to apply fertilizers during sowing.

Sowing date and seeding rate are critical to achieving high yields in winter and spring wheat. The sowing dates vary from region to region based on the temperature, variety, and water availability. To decide on the sowing date, the farmer should consider the life cycle length of the variety chosen and the expected environmental conditions during the flowering stage of the crop. Winter wheat cultivars are generally sown from September to November. More specifically, in India, dwarf wheat varieties with a long life cycle can be sown at the beginning of November. On the other hand, in Minnesota (U.S), wheat is sown from the start of September until the first 2 weeks of October. Michigan State University mentions that when planting after the 1st of October, a yield loss of 0.6 bushels per day is expected (5). The aim is to have a good crop establishment, with the successful emergence of the first true leaf before the first autumn “killing” frost occurs (4). Farmers should not sow too early since wheat plants with excessive vegetative growth are sensitive to winter kill, while there is also a higher risk for pest infestation. 

Wheat Plant Population and Seeding Requirements per hectare 

The seeding rate and plant population per hectare or acre should be adapted to the targeted number of plants at harvest. Generally, for winter wheat, an average number is 1,000.000 plants per acre or 2,500.000 plants per hectare, while for spring and Durum, is 1,400.000 plants per acre (6) or 3,500.000 plants per hectare. In poor rainfall conditions and lack of irrigation, the final number could be less. However, there can be great deviations from these numbers. Acconding to Penn State University (10), the desired plant population for winter wheat in Pennsylvania is 1,500.000 plants per acre or 3,750.000 plants per hectare (28 to 34 plants/sq ft). This requires a seeding rate of 4,250,000 seeds per hectare or 1,750.000 seeds per acre (or 20–23 seeds per foot in a 7-inch row).  

Seed rating can also be affected by the seed size. Row spacing could vary between 15 and 22.5 cm (5.9 to 8.7 inches). In irrigated fields, smaller row spaces are preferred (15-18 cm – 5.9-7 in). Seeding of winter wheat generally takes place at a depth of 2-5 cm (1-1.6 inches). When temperature and soil moisture are at favorable levels, seeds can be sown closer to the surface (2 cm) to accelerate emergence. Seeds of dwarf varieties can be sown at a smaller depth. 

The seeds can be treated with an appropriate broad-spectrum (active or/and systemic) fungicide to protect them from seedling blights, common bunt, and loose smut fungi (7). Most seed treatments include more than one active ingredient for a broader protective spectrum. Common active compounds in fungicides up to 2020 are: Tebuconazole, Fluxapyroxad, Pyraclostrobin, Carboxin, Thiram, Difenoconazole, Penflufen, Fludioxonil, Triticonazole, Sedaxane, Ipconazole, Mefenoxam, Metalaxyl, Prothioconazole (8). You should always consult your local licensed agronomist. 

References

1. https://www.fao.org/land-water/databases-and-software/crop-information/wheat/en/
2. Wheat growth and physiology – E. Acevedo, P. Silva, H. Silva (fao.org)
3. https://iiwbr.icar.gov.in/wp-content/uploads/2018/02/EB-52-Wheat-Cultivation-in-India-Pocket-Guide.pdf
4. Winter wheat seeding dates | UMN Extension
5. Planting the 2022 wheat crop – Wheat (msu.edu)
6. Seeding rate for small grains | UMN Extension
7. The Importance of Wheat Seed Treatments | CropWatch | University of Nebraska–Lincoln (unl.edu)
8. MF2955 Seed Treatment Fungicides for Wheat Disease Management 2020 (ksu.edu)
9. https://iiwbr.icar.gov.in/wp-content/uploads/2018/02/EB-52-Wheat-Cultivation-in-India-Pocket-Guide.pdf
10. https://extension.psu.edu/planting-winter-wheat-in-dry-soils

Farooq, S., and Azam, F. (2005). The use of cell membrane stability (CMS) technique to screen for salt tolerant wheat varieties. J. Plant Physiol. 163, 629–637. doi: 10.1016/j.jplph.2005.06.006

Kumar, P. V., Rao, V. U. M., Bhavani, O., Dubey, A. P., Singh, C. B., & Venkateswarlu, B. (2016). Sensitive growth stages and temperature thresholds in wheat (Triticum aestivum L.) for index-based crop insurance in the Indo-Gangetic Plains of India. The Journal of Agricultural Science, 154(2), 321-333.

Marcela, H., Karel, K., Pavlína, S., Petr, Š., Petr, H., Kateřina, N., … & Miroslav, T. (2017). Effect of heat stress at anthesis on yield formation in winter wheat. Plant, Soil and Environment, 63(3), 139-144.

Mojid, M. A., Mousumi, K. A., & Ahmed, T. (2020). Performance of wheat in five soils of different textures under freshwater and wastewater irrigation. Agricultural Science, 2(2), p89-p89.

Rahman, M. A., Chikushi, J., Yoshida, S., Yahata, H., and Yasunaga, E. (2005). Effect of high air temperature on grain growth and yields of wheat genotypes differing in heat tolerance. J. Agric. Meteorol. 60, 605–608. doi: 10.2480/agrmet.605

Ren, A. X., Min, S. U. N., Wang, P. R., Xue, L. Z., Lei, M. M., Xue, J. F., … & YANG, Z. P. (2019). Optimization of sowing date and seeding rate for high winter wheat yield based on pre-winter plant development and soil water usage in the Loess Plateau, China. Journal of integrative agriculture, 18(1), 33-42.

Shannon, M.C. 1997. Adaptation of plants to salinity. Adv. Agron., 60: 75-120.

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