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Irrigation Management of Soft White Spring Wheat

 
 
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 Introduction
Soft white spring wheat (SWSW) continues to be an important crop in the irrigated areas of southern Alberta. Over the past 15 years, the number of seeded acres has decreased from a high in 1985 of 450,000 acres to an average of 170,000 acres.

Pastry flour, which requires a low protein content, is the primary use of this particular wheat. Good irrigation management has shown to be one of the important factors in optimizing yield and maintaining low protein content.

This particular crop is usually seeded between April 21 and May 7, and soil temperature must be above 4°C for proper germination. The optimum growing temperature range is between 15 and 25°C, and SWSW takes approximately 115 days to reach maturity. On average this crop requires about 480 mm (19 in.) of moisture during the growing season. It has a poor tolerance to salts during the germination and seedling stages, but once established, it is more salt tolerant.

In areas where there are no soil restrictions, an active root zone of approximately 1.0 m (3.3 ft.) develops. In general, soil moisture levels should be maintained above 50% available moisture in the active root zone throughout the growing season. The two most critical times to ensure sufficient water are during tiller initiation and flowering. Moisture stress during these periods can cause significant yield or quality reductions.

Like other cereals, this crop requires nitrogen fertilizer for maximum yields. But unless the nitrogen requirements are balanced with an adequate water supply, the protein content can rise to an unacceptable level. Growers should have their soils tested for available nitrogen and then fertilize according to the projected crop yield.

High protein levels are likely to result not only from excess nitrogen fertilizer but also from drought stress during the latter part of the growing season. Farmers should irrigate to maintain adequate soil moisture throughout the root zone for the entire crop growing season.

Pivot irrigation systems
Irrigation of soft wheat can start as soon as seeding has been completed. Light frequent water applications should be applied until the crop reaches the four leaf stage. Once this stage is reached, the amount of water applied during each irrigation should be increased and the entire root zone should be filled to near field capacity. This crop uses large amounts of water between boot and soft dough growth stages, and moisture levels must be maintained throughout. Pivot irrigation should continue until the crop has reached the soft to mid-dough stage.

Wheel move irrigation systems
Good spring soil moisture is necessary for proper germination of this crop as early irrigation with a wheel move is not recommended. If poor moisture conditions exist, it is possible to apply a three or four hour set, but this is very labour intensive and does not guarantee good establishment. Growers should expect to irrigate soft wheat at least three times, using wheel move systems, if proper moisture levels are to be maintained and high quality expected. Proper timing of irrigations is critical with this crop.

Surface irrigation systems
A producer can expect to surface irrigate soft wheat twice during the growing season. The first irrigation should not be started before the crop reaches the four or five leaf stage. Irrigating before this stage can cause crop yellowing and stunting.

Experience and research have shown
  • Moisture stress during tillering or flowering can cause high yield reductions.
  • Soft wheat uses high amounts of moisture until soft dough stage.
  • Keeping soil moisture levels at or above 75% increases the potential for lodging but also increases crop quality by lowering protein levels.
  • The last irrigation should be completed by the middle of August if proper field conditions are to exist for harvesting.
This information was prepared by the Irrigation Branch.



Old Agdex Reference. 561-13.		  
 
 
 
For more information about the content of this document, contact Alan Efetha.
This document is maintained by Deb Sutton.
This information published to the web on June 21, 2002.
Last Reviewed/Revised on February 12, 2008.