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Winter Wheat: Fertility Requirements and Assessing Survival


Assessing Survival

Spring is right around the corner, and it’s that time of year when winter wheat growers are starting to think about spring fertility requirements, and how their crop survived our Manitoba winter. Ideally, the optimum plant stand is over 20 healthy plants/ft2, but keep in mind that a stand of 10-15 plants/ft2 can still produce a profitable crop. There are three common ways to assess winter wheat survival including:

  1. Spring Growth: Likely the most common, this method requires that farmers wait until their winter wheat crop has broken dormancy and new growth is initiated in the field. Start by digging up plants in various spots in the field (ie. areas that had different levels of residue and snow cover). The plant roots should be rinsed and examined for new root growth and a healthy white crown. Count the plants per square foot that have these characteristics, and keep in mind that plants showing signs of leaf burn or are brown in color do not necessarily indicate winter kill.
  2. Bag Test: First, plants are dug up with caution not to damage the crown. After rinsing the crown and roots, the roots and leaves should be trimmed, leaving one inch of stem above the crown. Place the crowns in a Ziploc bag, and keep at room temperature. Repeat the rinsing and allow new air into the bag every two days. Healthy plants will grow new leaves and roots. If no new growth is observed after 6 days, consider it a victim of winter kill.
  3. Sod Extraction: This method involves farmers digging up several pieces of sod with a shovel. The pieces should be brought to room temperature while keeping the soil moist. After 5-7 days, look at the crowns for new root growth, which indicated the plant has survived.

A general reminder is that winter wheat plants need time to recover after our harsh prairie winters, so it’s important to scout the field as late as possible. New growth tends to be aided by cool, moist weather, so if conditions are warm and dry, stand establishment could be impacted and re-seeding may need to be considered.

Nitrogen Fertility and Protein Management

In general, the MB Soil Fertility Guide recommends 80-120 lbs/ac of nitrogen is required to optimize yield potential without compromising on protein levels in winter wheat. Many farmers tend to apply most of their N fertilizer in the fall, and apply the remainder in the spring, taking potential loss, stand assessments, and fertilizer costs into consideration. It’s important to note, that spring applications of N should be done early enough in the season to meet the crop’s early demand, as early N applications are important to stimulate tillering, especially if establishment was poor going into winter, or winter injury occurred. In the case of winter wheat, the plants use 30-40% of their total N requirement by the stem elongation stage (5-6 leaf).

Soil conditions across some parts of the province are dry, and it is recommended that farmers protect against N loss from volatilization. Volatilization is the loss of N resulting from breakdown of urea into free ammonia (NH3) at the soil surface. Conditions that increase risk of volatilization loss include: high temperatures, high soil pH, low rainfall, high surface residue levels, high winds, and low soil organic matter. If no rain is in the forecast, use urea treated with a urease inhibitor (like NBPT), or dribble band UAN. UAN could also be treated with a urease inhibitor, but most of the loss protection comes from for UAN from and placement. UAN or urea injection would avoid both volatilization and stranding, though few farmers have this option.

Winter wheat is very responsive to N fertilization. It’s important to remember that if soil N is low, an increase in yield can dilute protein content. A general rule of thumb is that if winter wheat protein is less that 11.5%, then the crop did not have enough N fertilizer to reach optimum yield potential.

More Information

Western Winter Wheat Initiative: Spring Assessment & Fertility:

https://www.growwinterwheat.ca/growing-winter-wheat/spring-assessment/

https://www.growwinterwheat.ca/growing-winter-wheat/fertility/

Manitoba Agronomists Conference:

Evaluating Nitrogen Fertilizer Sources for Winter Wheat by Dr. Tom Jensen:

https://umanitoba.ca/faculties/afs/agronomists_conf/media/Dec_14pm_6_Jensen_presentation.pdf

Winter Wheat – Breaking Through the Yield Ceiling by Ken Gross

https://www.mbcropalliance.ca/assets/uploads/images/12_-_CROP_-_Gross_Presentation.pdf

Manitoba Agriculture – Winter Wheat Production & Management:

https://www.gov.mb.ca/agriculture/crops/crop-management/winter-wheat.html#

Factsheet: Winter Survival and Spring Assessment of Winter Wheat

https://www.soilcc.ca/ggmp_fact_sheets/pdf/winter%20survival-factsheet.pdf